JP5581996B2 - Internal combustion engine - Google Patents

Description

  The present invention relates to an internal combustion engine including a variable valve mechanism.

  There is known a technique for improving the combustion efficiency of an internal combustion engine by using a variable valve system that variably controls the valve timing, operating angle, and lift amount of an intake / exhaust valve according to an operating state.

  For example, Patent Document 1 discloses a variable valve system that can variably control the valve timing, valve lift amount, and operating angle of two exhaust valves in an exhaust two-valve internal combustion engine. In this system, two actuators, a motor and a hydraulic pressure, are used to control the valve timing, valve lift amount, and operating angle of two exhaust valves according to the operating state.

  For example, a small operating angle is set for a low load, a medium operating angle (a size between the maximum operating angle and a minimum operating angle) for a low rotating high load, and a large operating angle for a high rotating high load.

JP 2001-355469 A

  However, in the configuration using two actuators of a motor and a hydraulic pressure to change the valve timing, valve lift amount, and operating angle of both exhaust valves as in Patent Document 1, the cost increases. Further, in an operating region where the flow in the cylinder is small, such as a low load, there is a possibility that the amount of HC emission will increase.

  Therefore, an object of the present invention is to provide a low-cost system that can avoid an increase in HC emission.

The present invention is an internal combustion engine provided with two exhaust valves per cylinder. One exhaust valve is driven by a fixed cam having a constant operating angle, and the other exhaust valve has an operating angle between a small operating angle smaller than the fixed cam operating angle and a larger operating angle larger than the fixed cam operating angle. It is driven by a variable cam provided with a variable operating angle mechanism. Furthermore, at least one of the opening timing or closing timing of the variable cam at the time of a small operating angle, Ri near between closing timing from the opening timing of the fixed cam, operating angle varying mechanism, the operating range of the internal combustion engine is a low rotation and high load region In this case, the operating angle of the variable cam is larger than the operating angle of the fixed cam in the high rotation and high load region so that the operating angle of the variable cam is equal to or smaller than the operating angle of the fixed cam. So as to change the lift characteristics.

  According to the present invention, in the case of a small operating angle, a one-valve period in which only one of the fixed cam and the variable cam is opened occurs, and the turbulence intensity of the exhaust gas in the exhaust port is increased during this period. As a result, the oxidation in the exhaust port is promoted, so that an increase in the HC emission amount can be avoided. Further, an inexpensive system that can change the valve timing, the valve lift amount, and the operating angle can be realized with a simple configuration in which one is a fixed cam and the other is an operating angle variable mechanism.

It is a block diagram of the working angle variable mechanism to which this invention is applied. It is a lift characteristic figure of a 1st embodiment. It is a driving | operation area | region map used for control of a working angle variable mechanism. It is a lift characteristic figure of a 2nd embodiment. It is a lift characteristic figure of a 3rd embodiment.

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

  FIG. 1 is a configuration diagram of an operating angle variable mechanism 1 used in the first embodiment.

  The variable operating angle mechanism 1 is attached to an exhaust two-valve internal combustion engine having two exhaust valves in each cylinder, and opens and closes one exhaust valve with a swing cam 8 and the other exhaust valve with a fixed cam 9. Is.

  Since the valve driving principle of the swing cam 8 is the same as that of the variable operating angle mechanism disclosed in, for example, Japanese Patent Application Laid-Open No. 2003-201886, only the outline will be described.

  The drive shaft 2 and the control shaft 5 are each disposed substantially parallel to the cylinder row of the internal combustion engine. The drive shaft 2 rotates in synchronization with the crankshaft of the internal combustion engine via a timing chain or the like.

  An eccentric cam 3 is fixed to the outer periphery of the drive shaft 2 by press fitting or the like, and a first link 4 is fitted on the outer periphery of the eccentric cam 3 so as to be rotatable relative to the eccentric cam 3.

  A gear 13 is fixed near one end of the drive shaft 2 by press fitting or the like, and the gear 13 is engaged with a pinion gear 15 of the actuator 14. That is, the control shaft 5 can be rotated by driving the actuator 14. The actuator 14 is controlled based on the engine speed detected by the crank angle sensor 17 and the engine load detected by the air flow meter 18 by the engine control unit (ECU) 16. Details of the control will be described later.

  The control shaft 5 includes an eccentric cam portion 5a having an outer peripheral portion formed in the shape of an eccentric cam, and a rocker arm 6 is externally fitted thereto so as to be relatively rotatable.

  One end of the first link 4 is connected to one end of the rocker arm 6 via a connecting pin or the like so as to be relatively rotatable. One end of the second link 7 is connected to the other end of the rocker arm 6 via a connecting pin 10 so as to be relatively rotatable. The other end of the second link 7 is connected to the swing cam 8 via a connecting pin 11 so as to be relatively rotatable. The swing cam 8 is fitted on the outer periphery of the drive shaft 2 so as to be relatively rotatable.

  The fixed cam 9 is fixed to the outer periphery of the drive shaft 2 by press fitting or the like.

  The connecting pin 10 is positioned in the pin hole of the rocker arm 6 by a lock bolt 12 and an adjuster screw (not shown) arranged at a position facing the lock bolt 12 with the connecting pin 10 interposed therebetween. Made. When the position of the connecting pin 10 changes, the position of the second link 7 also changes, and the posture of the swing cam 8 changes accordingly. Therefore, in the adaptation when the operating angle variable mechanism 1 is attached to the internal combustion engine, the posture of the swing cam 8 is adjusted by an adjuster screw or the like.

  With the configuration as described above, when the drive shaft 2 rotates, the first link 4 moves in translation via the eccentric cam 3, and accordingly, the rocker arm 6 swings around the axis of the eccentric cam portion of the control shaft 5. The swing cam 8 swings around the drive shaft 2 via the second link 7. Thereby, the swing cam 8 opens and closes one exhaust valve in conjunction with the rotation of the internal combustion engine via a valve lifter or the like.

  Then, by controlling the rotation of the control shaft 5 with the actuator 14, the axial center position of the eccentric cam portion 5a that becomes the rocking center of the rocker arm 6 can be changed, and the lift characteristics of the exhaust valve can be continuously changed. . For example, as the distance between the shaft center of the eccentric cam portion 5a and the shaft center of the drive shaft 2 approaches, the operating angle increases, and the lift amount increases accordingly. When the operating angle and the lift amount change, the center position (center angle) of the operating angle does not move, and the size from the central angle to the timing of valve opening and closing changes. The variable amount of the operating angle of the swing cam 8 and the valve timing will be described later.

  When the drive shaft 2 rotates, the fixed cam 9 fixed to the drive shaft 2 also rotates, and the fixed cam 9 opens and closes the other exhaust valve in the same manner as a general internal combustion engine. That is, the fixed cam 9 has no variable mechanism, and the operating angle and the like are fixed.

  As described above, the operating angle variable mechanism 1 variably controls the valve lift amount and the operating angle only for one exhaust valve of the exhaust two-valve internal combustion engine. Since only one of the two exhaust valves is variably controlled, the valve reaction force acting on the rocker arm 6, the second link, etc. is halved compared to the configuration in which the two exhaust valves are variably controlled. For this reason, the strength required for the rocker arm 6 and the like is low, and the output required for the actuator 14 is low, and as a result, the parts can be reduced in size and weight.

  Further, in the operating angle variable mechanism 1, the influence of variations such as manufacturing tolerances of each part on the valve opening / closing timing is greater than that of the fixed cam 9 particularly at a small operating angle.

  This is because even if the swing cam 8 driven by the fixed cam 9 and the variable operating angle mechanism 1 has the same operating angle, the operating angle can be reduced by the variable operating angle mechanism 1 that can be adjusted from a small operating angle to a large operating angle. This is because the variation in valve opening / closing timing is larger than that of the fixed cam 9. That is, when the operating angle variable mechanism 1 having the swing cam 8 in which the cam crest is set so that the change in the lift amount is steep at the beginning of the lift and gradually becomes gentle thereafter, the cam crest is adjusted. This is because the portion where the lift amount changes sharply is mainly used.

  For this reason, the operating angle variable mechanism 1 is provided with a mechanism for adjusting the deviation of the valve opening / closing timing due to the above-described variation, and it is necessary to adjust the valve opening / closing timing when assembling the internal combustion engine.

  However, in the configuration of the present embodiment, the valve opening / closing timing at a small operating angle is governed by the cam profile of the fixed cam 9, so that the influence of the variation is reduced compared to the configuration in which the two exhaust valves are variably controlled. Adjustment work becomes easy.

  Note that the operating angle variable mechanism 1 shown in FIG. 1 is merely an example, and other mechanisms may be used as long as the operating angle can be variably controlled only for one exhaust valve.

  Next, the valve lift amount and the operating angle (lift characteristic) by the operating angle variable mechanism 1 will be described with reference to FIG.

  FIG. 2 is a diagram illustrating the lift characteristics of the present embodiment. The solid line I in the figure indicates the lift characteristic of the intake valve, the solid line Ef indicates the lift characteristic of the exhaust valve driven by the fixed cam 9, and the solid lines E11 to E13 indicate the minimum operating angle of the exhaust valve driven by the swing cam 8, respectively. The lift characteristics at the intermediate operating angle and the maximum operating angle are shown. In the figure, a chain line Cv indicates the center angle of the swing cam 8, and a chain line Cf indicates the center angle of the fixed cam 9.

  The operating angle of the fixed cam 9 is set to a size that does not cause exhaust interference with other cylinders. Specifically, it sets based on the pressure waveform in an exhaust passage for every internal combustion engine to which this embodiment is applied. For example, when the exhaust stroke is performed at an interval of 180 degrees in the in-line four cylinders, the exhaust interference can be avoided if the operating angle is in a range smaller than 200 to 220 degrees.

  The operating angle of the swing cam 8 is a minimum operating angle (lift characteristic E11) smaller than the operating angle of the fixed cam 9, a maximum operating angle (lift characteristic E13) larger than the operating angle of the fixed cam 9, and an intermediate between them. The intermediate operating angle (lift characteristic E12) can be switched.

  Further, the central angle of the swing cam 8 is set to an advance side with respect to the center angle of the fixed cam 9, and the valve opening timing of the lift characteristic E11 and the lift characteristic of the fixed cam 9 when the swing cam 8 is at the minimum operating angle. The valve opening timing of I is substantially matched.

  The exhaust valve opening timings of the lift characteristics E11 to E13 are set to timings at which the expansion ratios are suitable when the engine rotation speed is low speed rotation, medium speed rotation, and high speed rotation, respectively.

  Looking at the cylinder as a whole, it is the exhaust valve on the fixed cam 9 side that closes last in any of the lift characteristics E11 to E13. That is, the closing timing of the exhaust valve of the cylinder is the closing timing of the exhaust valve on the fixed cam 9 side. On the other hand, since the opening timing of the exhaust valve on the fixed cam 9 side is substantially the same as the lift characteristic E11 with the slowest opening timing of the exhaust valve, the opening timing of the exhaust valve on the cylinder is the lift timing of the exhaust valve on the swing cam 8 side. It depends on the characteristics.

  Therefore, when the lift characteristics E11 to E13 are switched, only the opening timing is changed without changing the closing timing of the exhaust valve of the cylinder. That is, the opening timing of the exhaust valve can be changed by using only the operating angle variable mechanism shown in FIG. 1 without using the phase variable mechanism that changes the phases of the crankshaft and the drive shaft 2. .

  In addition, the pump loss when the overlap period is extended can be reduced as compared with the case of using a phase variable mechanism that drives two exhaust valves simultaneously. That is, when the phase variable mechanism is used, if the exhaust valve closing timing is delayed in order to lengthen the overlap period, the opening timing is also delayed. For this reason, depending on the length of the overlap period, the exhaust valve opening timing comes after the bottom dead center, and the work of compressing the exhaust occurs. On the other hand, in the configuration of this embodiment, even if the closing timing of one exhaust valve is delayed until after bottom dead center, the exhaust valve on the fixed cam 9 side opens before bottom dead center, so the exhaust is compressed. The work to be done is small compared to the case of the phase variable mechanism.

  Due to the characteristics of the variable operating angle mechanism 1, the lift amount decreases as the operating angle of the swing cam 8 decreases, and the lift amount increases as the operating angle increases.

  Here, each lift characteristic mentioned above is demonstrated.

  In the lift characteristic E11 where the operating angle of the swing cam 8 is the minimum, the exhaust valves on the swing cam 8 side and the fixed cam 9 side are opened almost simultaneously. Then, the exhaust valve on the swing cam 8 side is closed first, and only the exhaust valve on the fixed cam 9 side is opened (one-valve period II). Thereafter, the intake valve is opened to enter an overlap period, and the exhaust valve on the fixed cam 9 side is closed.

  In the lift characteristic E11 as described above, since the opening timings of both exhaust valves are almost simultaneous, the lift characteristic 12 and the lift characteristic 13 in which the exhaust valve on the swing cam 8 side opens earlier than the exhaust valve on the fixed cam 9 side, In comparison, the time for the combustion gas to stay in the cylinder becomes longer. Therefore, the in-cylinder temperature rise and in-cylinder oxidation are promoted.

  Further, in the one-valve period II, exhaust is discharged only from the exhaust valve on the fixed cam 9 side, so that the turbulence intensity in the exhaust port is increased compared to the case where the exhaust is discharged from both exhaust valves. The oxidation of is promoted.

  Further, during the overlap period, the exhaust gas is pushed out to the exhaust port with an internal EGR in which the exhaust gas recirculates from the exhaust port into the cylinder or the intake air flows into the cylinder according to a pressure difference between the intake passage and the exhaust passage. Scavenging effect is obtained.

  Here, the overlap period is a one-valve period II, and in the case of internal EGR, exhaust gas is introduced only from one exhaust port. Increases turbulence intensity. For this reason, EGR gas will be in the state fully stirred, and the combustion stability at the time of EGR introduction | transduction can be improved. In addition, when scavenging is performed, oxidation is promoted in the port by exhausting only from one of the exhaust ports.

  In addition, exhaust interference of other cylinders can be reduced. That is, for example, in an internal combustion engine that explodes at a crank angle interval of 180 degrees, such as an in-line four-cylinder internal combustion engine, if the exhaust operating angle is wide, there is a risk of receiving exhaust interference from other cylinders at low speeds. However, if the operating angle of the fixed cam 9 is set to a size that is not subject to exhaust interference, the operating angle of the swing cam 8 of the lift characteristic E11 is smaller than the operating angle of the fixed cam 9, so that exhaust interference can be avoided. As a result, the residual gas in the cylinder is reduced, the volume efficiency in the fully open region is improved, and the fully open performance is improved.

  If the oxidation in the exhaust port is promoted, the unburned components are burned and the heat energy of the exhaust increases, so in the case of an internal combustion engine with a turbocharger, the response of the turbocharger is delayed. Can be eliminated.

  In the lift characteristic E13 with the maximum operating angle of the swing cam 8, the exhaust valve on the swing cam 8 side is opened first, and only the exhaust valve on the swing cam 8 side is open (single valve period) I). After the exhaust valve on the fixed cam 9 side is opened, the two exhaust valves are opened, and after the intake valve is opened and the valve overlap period is reached, the swing cam 8 side and the fixed valve are fixed. The exhaust valve on the cam 9 side closes almost simultaneously.

  In the lift characteristic E13 as described above, in-port oxidation is promoted in the one-valve period I as in the one-valve period II of the lift characteristic E11. Further, due to the characteristics of the variable operating angle mechanism 1, since the valve lift amount increases as the operating angle increases, the exhaust flow path (exhaust front) when the exhaust valve opens is wider than the lift characteristics E11 and E12. . For this reason, the passage resistance of the exhaust port is lowered and the exhaust loss is reduced.

  Further, only the opening timing can be advanced without changing the closing timing of the exhaust valve, so that the exhaust valve opening timing is set to an expansion ratio suitable for the engine operating state without causing an increase in the in-cylinder residual gas. be able to. If the expansion ratio is suitable for the engine operating state, exhaust loss can be reduced, thermal efficiency can be improved, and fully open performance can be improved.

  When the lift characteristic E12 between the minimum and maximum operating angles of the swing cam 8 is set, the exhaust valve on the swing cam 8 side is opened first, and only the exhaust valve on the swing cam 8 side is opened. The state (one-valve period I) is entered. Here, the one-valve period I is shorter than the one-valve period I of the lift characteristic E3 having the maximum operating angle.

  Then, after the exhaust valve on the fixed cam 9 side is opened, the two exhaust valves are opened. The exhaust valve on the swing cam 8 side is closed before the intake valve is opened, and thereafter, only the exhaust valve on the fixed cam 9 side is opened (one-valve period II) and the overlap period is reached. The exhaust valve on the 9th side is also closed. Here, the one-valve period II is shorter than the one-valve period II of the lift characteristic E11 in which the operating angle is minimum.

  In the lift characteristic E12 as described above, in the one-valve period I, in-port oxidation is promoted by turbulent flow enhancement in the port. Moreover, the stirring effect of internal EGR is acquired in the overlap period in the one-valve period II. Furthermore, as with the lift characteristic E13, it is possible to improve the fully open performance by setting the exhaust valve opening timing according to the engine operating state.

  Next, switching control of the lift characteristics E11 to E13 by the ECU 16 will be described with reference to FIG. FIG. 3 is an operating region map of the internal combustion engine used by the ECU 16 for controlling the operating angle variable mechanism, where the vertical axis represents the engine load and the horizontal axis represents the engine rotation speed. The solid line in the figure indicates the full load state.

  Region I is a region during start-up and idling (cold and warm-up), region II is a region that is traveling at a low rotation and low load, region III is a region that is traveling at a low rotation and load, and region IV is A low rotation high load region, a region V indicates a medium rotation high load region, and a region VI indicates a high rotation high load region.

  The ECU 16 determines which region the current operation region corresponds to based on signals from the crank angle sensor 17 and the air flow meter 18 and signals from an ignition switch (not shown), and lift characteristics for each region. Switch.

  If the ECU 16 determines that it is in the region I, the ECU 16 sets the lift characteristic E11. In the region I, when idling, the main problem is to reduce the HC emission amount. Furthermore, in the case of idling operation at start-up or cold-down, the fuel injection amount is increased, and the temperature of the cylinder inner wall surface is low, so that raising the cylinder temperature is also a problem.

  Therefore, the lift characteristic E11 is set to promote in-cylinder oxidation and increase the in-cylinder temperature. That is, by quickly increasing the in-cylinder temperature to the warm-up end temperature, the fuel injection amount increase at the start is terminated, the in-cylinder oxidation is promoted, and the exhaust gas is increased by increasing the turbulent flow intensity in the exhaust port during the one-valve period II. Reduce HC emissions by promoting oxidation in the port.

  The ECU 16 sets the lift characteristic E11 even when it is determined as the region II. Since the region II is a low rotation / low load region, improvement of fuel efficiency is a problem.

  Therefore, the lift characteristic E11 is used to promote the stirring of the internal EGR. That is, the overlap period overlaps with the one-valve period II, and the stirring of the internal EGR is promoted to improve the combustion stability. Region II is a region where it is difficult to increase the amount of EGR because combustion tends to become unstable. However, if the combustion stability is improved as described above, more internal EGR can be introduced, resulting in pump loss. This is because the fuel efficiency is improved since the specific heat ratio is improved.

  If the ECU 16 determines that the region is III, the ECU 16 sets the lift characteristic E12. Region III is a low-revolution medium load region, and as with region II, improvement in fuel efficiency is a problem. However, since the amount of intake air increases as the load is larger than in region II, the amount of exhausted combustion gas also increases. Since the combustion speed increases as the intake air amount increases, the combustion stability is higher than in region II, and a large amount of EGR gas can be introduced.

  Therefore, in order to accelerate the stirring of the internal EGR by the one-valve period II and to discharge more combustion gas at a larger operating angle and lift amount than the lift characteristic E11, the lift characteristic E12 is set.

  The ECU 16 sets the lift characteristic E11 when determining that the region is the region IV. Since the region IV is a low-rotation and high-load region such as a transient state of acceleration, for example, improvement of fully opened performance is a main issue.

  Therefore, the lift characteristic E11 is set to optimize the expansion ratio and obtain the scavenging effect during the overlap period. In other words, by delaying the opening timing of the exhaust valve to make the expansion ratio suitable for the low rotation region, the residual gas amount in the cylinder and the exhaust loss are reduced, and further, the scavenging effect during the overlap period is also utilized. , Improve thermal efficiency and improve full-open performance.

  Further, since the exhaust valve closing timing when viewed as the whole cylinder is the closing timing of the exhaust valve on the fixed cam 9 side, it is possible to avoid exhaust interference with other cylinders, and furthermore, combustion by the stirring effect of EGR gas during the one-valve period II Since stability is improved, acceleration performance can be improved in a transient state of acceleration.

  If the ECU 16 determines that it is in the region V, the ECU 16 sets the lift characteristic E12. Since the region V is a middle-rotation high-load region, improvement of the fully open performance is a main issue.

  Therefore, the lift characteristic E12 is set to optimize the expansion ratio. That is, by setting the exhaust valve opening timing so as to have an expansion ratio suitable for medium speed rotation, the residual gas in the cylinder and the exhaust loss are reduced, the thermal efficiency is improved, and the full opening performance is improved.

  When the ECU 16 determines that the region VI is set, the ECU 16 sets the lift characteristic E13. Since the region VI is a high-rotation and high-load region, improvement of the fully open performance is a main issue.

  Therefore, the lift characteristic E13 is set to optimize the expansion ratio and expand the exhaust port. In other words, by setting the exhaust valve opening timing so as to achieve an expansion ratio suitable for high-speed rotation, the residual gas in the cylinder and the exhaust loss are reduced to improve the thermal efficiency, and the valve lift amount is increased to increase the exhaust port. By expanding, it will improve the fully open performance.

  For areas other than the above-described areas, what kind of performance should be emphasized in the area for the vehicle to which this embodiment is applied, for example, which of fuel efficiency performance, output performance, or exhaust performance is prioritized? Accordingly, it is set which of the lift characteristics E11 to E13 is selected.

  As described above, in the present embodiment, the following effects can be obtained.

  (1) In an exhaust two-valve internal combustion engine, one exhaust valve is driven by a fixed cam 9 having a lift characteristic that can avoid exhaust interference, and the other exhaust valve is fixed from a small operating angle smaller than the operating angle of the fixed cam 9. It is driven by a swing cam 8 provided with a variable operating angle mechanism 1 that can change the operating angle between operating angles larger than the operating angle of the cam 9. At the minimum operating angle, the opening / closing timing of the swing cam 8 is between the opening timing and the closing timing of the fixed cam 9. Thereby, at the minimum operating angle, there occurs a period in which the exhaust valve on the fixed cam 9 side is opened and the exhaust valve on the swing cam 8 side is closed. During this period, the turbulence intensity of the exhaust gas in the exhaust port Becomes stronger. As a result, effects such as promotion of oxidation in the exhaust port or promotion of stirring of the internal EGR can be obtained. Further, when the swing cam 8 has the minimum operating angle, exhaust interference can be avoided.

  (2) Since the center angle position of the swing cam 8 is on the more advanced side than the center angle position of the fixed cam 9, only the exhaust valve on the fixed cam 9 side is closed after the exhaust valve on the swing cam 8 side is closed. An open one-valve period II occurs, promoting oxidation in the exhaust port.

  (3) The variable operating angle mechanism 1 is configured so that the operating angle of the swing cam 8 is equal to or less than the operating angle of the fixed cam 9 in the low rotation and high load region, and the swing angle in the high rotation and high load region. The lift characteristic is changed so that the operating angle of the moving cam 8 becomes larger than the operating angle of the fixed cam 9. Thereby, in the transient state of acceleration (low rotation and high load region), the exhaust valve closing timing when viewed as the whole cylinder is the closing timing of the fixed cam 9, so that the exhaust interference can be suppressed. In addition, combustion stability is improved by promoting the stirring of the internal EGR during the one-valve period II. By suppressing these exhaust interferences and improving combustion stability, acceleration performance can be improved. Furthermore, if the opening timing at the maximum operating angle is set to an expansion ratio suitable for the high rotation and high load region, the full opening performance is improved by reducing the residual gas in the cylinder, reducing the exhaust loss, and the like. Therefore, both acceleration performance and fully open performance can be achieved.

  (4) In the variable operating angle mechanism 1, the opening timing of the fixed cam 9 is earlier than the opening timing of the swing cam 8 during the cold operation, and the opening timing of the swing cam 8 is the opening timing of the fixed cam 9 in a high rotation and high load region. The lift characteristics are changed so as to be earlier than the timing. The center angle position of the swing cam 8 is on the more advanced side than the center angle position of the fixed cam 9. As a result, the exhaust valve opening timing is relatively delayed during the cold operation, so that the in-cylinder oxidation of the combustion gas is promoted, whereby the rise in the in-cylinder temperature is promoted and the HC emission amount is reduced. On the other hand, in the high-rotation and high-load region, the fully open performance is improved as in (3) above.

  In the above description, the engine rotational speed and the load are each divided into three regions, and the three types of lift characteristics are switched according to the regions. However, the regions are further divided into three or more types according to this. The lift characteristics may be switched or continuously changed.

  Further, as described above, in the present embodiment, the opening / closing timing of the exhaust valve can be changed without providing the phase variable mechanism, and the same effect as that provided with the phase variable mechanism can be obtained. However, a phase variable mechanism may be provided to change the opening / closing timing of the exhaust valve more widely.

  A second embodiment will be described.

  In this embodiment, the configuration of the operating angle variable mechanism 1 is basically the same as that of the first embodiment, but the lift characteristics of the exhaust valves on the swing cam 8 side and the fixed cam 9 side are different.

  FIG. 4 is a diagram showing the lift characteristics of this embodiment. The solid line I in the figure indicates the lift characteristic of the intake valve, the solid line Ef indicates the lift characteristic of the exhaust valve driven by the fixed cam 9, and the solid lines E21 to E23 indicate the minimum operating angle of the exhaust valve driven by the swing cam 8, respectively. The lift characteristics at the intermediate operating angle and the maximum operating angle are shown. In the figure, a chain line Cv indicates the center angle of the swing cam 8, and a chain line Cf indicates the center angle of the fixed cam 9.

  The operating angle of the fixed cam 9 is set to a size that does not cause an overlap period and does not cause exhaust interference with other cylinders.

  The operating angle of the swing cam 8 is a minimum operating angle (lift characteristic E21) smaller than the operating angle of the fixed cam 9, a maximum operating angle (lift characteristic E23) larger than the operating angle of the fixed cam 9, and an intermediate between them. The intermediate operating angle (lift characteristic E22) can be switched.

  The central angle of the oscillating cam 8 is set to be retarded from the central angle of the fixed cam 9, the valve closing timing of the lift characteristic E 21 when the oscillating cam 8 is at the minimum operating angle, and the lift characteristic I of the fixed cam 9. Make the valve closing timing almost the same.

  The lift characteristics E22 and E23 set the closing timing of the exhaust valve so as to provide an overlap period.

  Looking at the cylinder as a whole, in any case of the lift characteristics E21 to E23, the exhaust valve on the fixed cam 9 side is first opened. That is, the opening timing of the exhaust valve of the cylinder is the opening timing of the exhaust valve on the fixed cam 9 side. On the other hand, since the closing timing of the exhaust valve on the fixed cam 9 side is substantially the same as the lift characteristic E21 with the earliest closing timing of the exhaust valve, the closing timing of the exhaust valve on the cylinder is the lift timing of the exhaust valve on the swing cam 8 side. It depends on the characteristics.

  Therefore, when the lift characteristics E21 to E23 are switched, only the closing timing is changed without changing the opening timing of the exhaust valve of the cylinder without using the phase variable mechanism.

  Next, each lift characteristic mentioned above is demonstrated.

  In the lift characteristic E21 where the operating angle of the swing cam 8 is the minimum, the exhaust valve on the fixed cam 9 side is opened first, and the one-valve period III is reached until the exhaust valve on the swing cam 8 side is opened. Thereafter, both exhaust valves are opened, and both exhaust valves are closed almost simultaneously. In such a lift characteristic E21, since the turbulent flow intensity in the exhaust port increases during the one-valve period III, the oxidation in the exhaust port is promoted.

  In the lift characteristic E23 where the operating angle of the swing cam 8 is the maximum, the exhaust valve on the fixed cam 9 side and the exhaust valve on the swing cam 8 side open almost simultaneously. Then, the exhaust valve on the fixed cam 9 side is closed first, and the one-valve period IV is reached, and the intake valve is opened and overlapped in the middle of the one-valve period IV. In such a lift characteristic E23, when the internal EGR is introduced, the one-valve period IV is set, and stirring of the introduced gas is promoted. The internal EGR amount can be increased by setting the closing timing of the exhaust valve on the swing cam 8 side to a timing that causes exhaust interference with other cylinders during the one-valve period IV.

  On the other hand, when scavenging is performed during the overlap period, oxidation in the port is promoted by exhausting only from one exhaust port.

  Further, when the operating angle is increased, the valve lift amount is also increased, so that the exhaust opening becomes larger and the exhaust passage resistance is reduced.

  In the lift characteristic E22 in which the operating angle of the swing cam 8 is between the maximum and the minimum, the exhaust valve on the fixed cam 9 side is opened first, and the one-valve period III is started. Thereafter, after the exhaust valves are opened, the exhaust valve on the fixed cam 9 side is closed first, and the one-valve period IV is started. Then, after the overlap period, the exhaust valve on the swing cam 8 side is closed. In such a lift characteristic E22, when the internal EGR is introduced, the one-valve period IV is established, and stirring of the introduced gas is promoted. Further, as with the lift characteristic E23, an effect of increasing the internal EGR amount by exhaust interference can be obtained.

  Next, switching control of the lift characteristics E21 to E23 by the ECU 16 will be described with reference to FIG. Regions I to VI are the same as in the first embodiment.

  If the ECU 16 determines that it is in the region I, it sets the lift characteristic E21. Since the region I is a region during start-up or idling, reduction of HC emissions and temperature rise in the cylinder are the main issues. Therefore, the lift characteristic E21 is set in order to promote oxidation by increasing the turbulence intensity in the exhaust port during the one-valve period III.

  If the ECU 16 determines that the region is II, the ECU 16 sets the lift characteristic E22. Region II is a low rotation and low load region, and improvement of fuel efficiency is a main issue.

  Therefore, the lift characteristic E22 is set for increasing the internal EGR amount and stirring. That is, by delaying the closing timing of the exhaust valve on the swing cam 8 side, exhaust interference is caused to increase the amount of internal EGR, and the combustion stability is improved by the stirring action of the internal EGR during the one-valve period IV. This will improve fuel efficiency by reducing pump loss and improving specific heat ratio.

  The lift characteristic E23 may be used. This is because there is a difference in the length of the valve overlap period, that is, the amount of internal EGR introduced, but basically the same effect is obtained.

  When the ECU 16 determines that the region is III, the ECU 16 sets the lift characteristic E23. Since the region III is a low-revolution mid-load region, improvement in fuel efficiency is a major issue.

  Therefore, as in the case of the region II, the lift characteristic E23 is set in order to improve the fuel efficiency by ensuring the combustion stability while increasing the internal EGR amount. The lift characteristic E22 may be used. This is because there is a difference in the length of the valve overlap period, that is, the amount of internal EGR introduced, but basically the same effect is obtained.

  If the ECU 16 determines that the region is the region IV, the ECU 16 sets the lift characteristic E23. Since the region IV is a low-rotation and high-load region, improvement of the fully open performance is a main issue.

  Therefore, the lift characteristic E23 is set in order to reduce the in-cylinder residual gas amount due to the scavenging effect during the overlap period. That is, by reducing the residual gas in the cylinder due to the scavenging effect due to the overlap period, a condition in which knocking does not easily occur and the intake air amount is increased to generate a higher output.

  The lift characteristic E22 may be used. This is because there is a difference in the length of the valve overlap period, that is, the amount of internal EGR introduced, but basically the same effect is obtained.

  If the ECU 16 determines that it is in the region V, the lift characteristic E22 is set. Since the region V is a middle-rotation high-load region, improvement of the fully open performance is a main issue.

  Therefore, the lift characteristic E22 is set to secure the exhaust process time. In terms of the cylinder as a whole, the exhaust process starts when the exhaust valve on the fixed cam 9 side opens, and ends when the exhaust valve on the swing cam 8 side closes. Therefore, the exhaust process time can be made longer by setting the lift characteristic E22 that the closing timing of the exhaust valve on the swing cam 8 side is slower than the closing timing of the exhaust valve on the fixed cam 9 side. As a result, the in-cylinder residual gas amount can be reduced and the fully open performance can be improved.

  Note that the closing timing of the lift characteristic E22 needs to be set in consideration of the choke time.

  If the ECU 16 determines that it is in the region VI, the lift characteristic E23 is set. Since the region VI is a high-rotation and high-load region, improvement of the fully open performance is a main issue.

  Therefore, the lift characteristic E23 is set to enlarge the exhaust port. That is, by expanding the exhaust opening, the passage resistance is reduced to reduce exhaust loss, and the fully open performance is improved.

  For other regions, as in the first embodiment, one of the lift characteristics is selected according to the performance required for the vehicle to be applied.

  As described above, in this embodiment, in addition to the same effects as those of the first embodiment, the following effects can be further obtained.

  (4) Since the center angle position of the swing cam 8 is on the retard side with respect to the center angle position of the fixed cam 9, a one-valve period III occurs in which only the exhaust valve on the fixed cam 9 side is open at the minimum operating angle. As a result, the turbulent flow intensity in the exhaust port increases, thereby promoting oxidation in the port and reducing the HC emission amount. Further, since the one-valve period IV in which only the exhaust valve on the swing cam 8 side is open occurs at the maximum operating angle, if the closing timing of the swing cam 8 is set to a timing at which exhaust interference occurs, the internal EGR is caused by exhaust interference. The amount increases. Furthermore, since it flows in from one exhaust port at this time, stirring of EGR gas is accelerated | stimulated and combustion stability improves. Therefore, the fuel efficiency improvement effect by internal EGR can be expected.

  A third embodiment will be described.

  In this embodiment, the configuration of the operating angle variable mechanism 1 is basically the same as that of the first embodiment, but the lift characteristics of the exhaust valves on the swing cam 8 side and the fixed cam 9 side are different.

  FIG. 5 is a diagram showing the lift characteristics of this embodiment. The solid line I in the figure indicates the lift characteristic of the intake valve, the solid line Ef indicates the lift characteristic of the exhaust valve driven by the fixed cam 9, and the solid lines E31 to E33 indicate the minimum operating angle of the exhaust valve driven by the swing cam 8, respectively. The lift characteristics at the intermediate operating angle and the maximum operating angle are shown. In the figure, a chain line Cv indicates the center angle of the swing cam 8, and a chain line Cf indicates the center angle of the fixed cam 9.

  The operating angle of the fixed cam 9 is set so as to have an overlap period and not to cause exhaust interference with other cylinders.

  The operating angle of the swing cam 8 is a minimum operating angle (lift characteristic E31) smaller than the operating angle of the fixed cam 9, a maximum operating angle (lift characteristic E33) larger than the operating angle of the fixed cam 9, and an intermediate between them. The intermediate operating angle (lift characteristic E32) can be switched.

  The center angle of the swing cam 8 is set to coincide with the center angle of the fixed cam 9 so that the opening / closing timing of the lift characteristic E32 matches the opening / closing timing of the lift characteristic I of the fixed cam 9.

  Looking at the entire cylinder, in the case of the lift characteristic E33, the exhaust valve on the swing cam 8 side is opened first and finally closed. In the case of the lift characteristic E32, both exhaust valves open and close at the same timing. In the case of the lift characteristic E31, the exhaust valve on the fixed cam 9 side is opened first and finally closed. That is, by switching the lift characteristics E31 to E33, the exhaust valve opening / closing timing of the cylinder can be changed without using the phase variable mechanism.

  Next, each lift characteristic mentioned above is demonstrated.

  In the lift characteristic E31 in which the operating angle of the swing cam 8 is minimum, the exhaust valve on the fixed cam 9 side opens first, and the one-valve period V is until the exhaust valve on the swing cam 8 side opens. Thereafter, both the exhaust valves are opened, and the exhaust valve on the swing cam 8 side is closed first, and only the exhaust valve on the fixed cam 9 side is opened. Then, after the intake valve is opened and the overlap period is reached, the exhaust valve on the fixed cam 9 side is closed.

  In such a lift characteristic E31, since the turbulent flow intensity in the exhaust port increases during the one-valve periods V and VI, the oxidation in the exhaust port is promoted. Further, since the overlap period is short, the amount of residual gas in the cylinder is also reduced, and for example, combustion stability at the time of cold start can be ensured. Further, when the internal EGR is introduced, the one-valve period VI is established, and the stirring of the introduced gas is promoted.

  In the lift characteristic E33 in which the operating angle of the swing cam 8 is the maximum, the exhaust valve on the swing cam 8 side is opened first and the one-valve period V is reached. Thereafter, both exhaust valves are in an open state, and the exhaust valve on the fixed cam 9 side is closed first, and only the exhaust valve on the swing cam 8 side is opened. After the intake valve is opened and an overlap period is reached, the exhaust valve on the swing cam 8 side is closed.

  In such a lift characteristic E33, when the internal EGR is introduced, the one-valve period VI is established, and the stirring of the EGR gas is promoted. In addition, by setting the opening timing of the exhaust valve on the swing cam 8 side to a timing at which the expansion ratio is suitable for the engine rotational speed, the in-cylinder residual gas can be reduced and the exhaust loss can be reduced.

  In the lift characteristic E32 where the operating angle of the swing cam 8 is between the maximum and minimum, both exhaust valves open and close at substantially the same timing. In such a lift characteristic E32, by setting the length of the overlap period so as to increase the scavenging effect, it is possible to reduce the in-cylinder residual gas amount and increase the intake charging efficiency. Further, by setting the opening timing of the exhaust valve to a timing at which the expansion ratio is suitable for the engine rotation speed, the in-cylinder residual gas can be reduced and the exhaust loss can be reduced.

  Next, switching control of the lift characteristics E31 to E33 by the ECU 16 will be described with reference to FIG. Regions I to VI are the same as in the first embodiment.

  If the ECU 16 determines that it is in the region I, it sets the lift characteristic E31. Since region I is a region during start-up and idling, reduction of HC emissions is a major issue.

  Therefore, in order to increase the turbulence intensity in the exhaust port during the one-valve period VI, the lift characteristic E31 is set. That is, by increasing the turbulence intensity, the oxidation in the outside air port is promoted to reduce the HC emission amount. Further, the lift characteristic E31 is the lift characteristics E31 to E33, and the overlap period is the shortest, so the cylinder residual gas amount is the smallest. For this reason, startability improves.

  If the ECU 16 determines that the region is II, the ECU 16 sets the lift characteristic E31. Region II is a low rotation / low load region, a low rotation / low load region, and improvement in fuel efficiency is a major issue.

  Therefore, the lift characteristic E31 is set for stirring the internal EGR. That is, by promoting the stirring of the EGR gas during the one-valve period VI, the combustion stability is improved and more EGR gas can be introduced, the pump loss is reduced, the specific heat ratio is improved, and the fuel efficiency performance is improved. Improve.

  Here, the length of the one-valve period VI may be set to the same lift characteristic E32 as the lift characteristic E31. Moreover, you may set to the lift characteristic E33. It is because the stirring effect of internal EGR is obtained similarly.

If the ECU 16 determines that the region is the region III, the ECU 16 sets the lift characteristic E33.
Since the region III is a low-revolution mid-load region, improvement in fuel efficiency is a major issue.

  Therefore, the lift characteristic E33 is set in order to ensure combustion stability while increasing the internal EGR amount. That is, by delaying the closing timing of the exhaust valve on the swing cam 8 side, exhaust interference is caused to increase the amount of internal EGR, and the combustion stability is improved by the stirring action of the internal EGR during the one-valve period IV. Thereby, the fuel consumption performance can be improved by reducing the pump loss and improving the specific heat ratio.

  If the ECU 16 determines that the region is IV, it sets the lift characteristic E32. Since the region IV is a low-rotation and high-load region, improvement of the fully open performance is a main issue.

  Therefore, the lift characteristic E32 is set to reduce the in-cylinder residual gas amount due to the scavenging effect during the overlap period. That is, if the in-cylinder residual gas is reduced by the scavenging effect due to the overlap period, knocking is less likely to occur and the amount of intake air is increased, so that a higher output can be generated.

  If the ECU 16 determines that the region is V, the ECU 16 sets the lift characteristic E32. Since the region V is a middle-rotation high-load region, improvement of the fully open performance is a main issue.

  Therefore, the lift characteristic E32 is set to optimize the expansion ratio. That is, by setting the exhaust valve opening timing at an expansion ratio suitable for medium speed rotation, the residual gas in the cylinder and the exhaust loss are reduced, the thermal efficiency is improved, and the full opening performance is improved.

  When the ECU 16 determines that the region VI is set, the ECU 16 sets the lift characteristic E33. Since the region VI is a high-rotation and high-load region, improvement of the fully open performance is a main issue.

  Therefore, the lift characteristic E33 is set to optimize the expansion ratio and expand the exhaust port. In other words, by setting the exhaust valve opening timing at an expansion ratio suitable for high-speed rotation, the residual gas and exhaust loss in the cylinder are reduced to improve the thermal efficiency, and the valve lift is increased to expand the exhaust port. This will improve the fully open performance.

  As described above, this embodiment can provide the same effects as those of the first embodiment.

  The present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made within the scope of the technical idea described in the claims. For example, in the above description, control for switching the operating angle of the swing cam 8 to the minimum operating angle, the intermediate operating angle, and the maximum operating angle has been described. However, the operating angle may be controlled continuously and variably.

DESCRIPTION OF SYMBOLS 1 Operating angle variable mechanism 2 Drive shaft 3 Eccentric cam 4 1st link 5 Control shaft 6 Rocker arm 7 2nd link 8 Oscillating cam 9 Fixed cam 10 Connecting pin 11 Connecting pin 12 Lock bolt 13 Gear 14 Actuator 15 Pinion gear 16 Engine control Unit (ECU)
17 Crank angle sensor 18 Air flow meter

Claims (5)

In an internal combustion engine with two exhaust valves per cylinder,
One exhaust valve is driven by a fixed cam with a constant operating angle,
The other exhaust valve is driven by a variable cam having an operating angle variable mechanism capable of changing an operating angle between a small operating angle smaller than the operating angle of the fixed cam and a large operating angle larger than the operating angle of the fixed cam.
Ri at least one of near-between closing timing from the open timing of the fixed cam of the on time of a small operating angle opening timing or closing timing of the variable cam,
When the operating range of the internal combustion engine is a low rotation and high load range, the variable operating angle mechanism is configured so that the operating angle of the variable cam is equal to or less than the operating angle of the fixed cam. The internal combustion engine , wherein the lift characteristic is changed so that the operating angle of the variable cam is larger than the operating angle of the fixed cam .   2. The internal combustion engine according to claim 1, wherein a center angle position of the variable cam is on a more advanced side than a center angle position of the fixed cam.   2. The internal combustion engine according to claim 1, wherein a center angle position of the variable cam is on a more retarded side than a center angle position of the fixed cam. The operating angle variable mechanism is configured so that the exhaust valve opening timing of the fixed cam is earlier than the exhaust valve opening timing of the variable cam when the internal combustion engine is in cold operation, and the variable cam of the variable cam is operating when the internal combustion engine is operating in a high rotation high load region. The internal combustion engine according to any one of claims 1 to 3 , wherein lift characteristics are changed so that an exhaust valve opening timing is earlier than an exhaust valve opening timing of the fixed cam. In an internal combustion engine with two exhaust valves per cylinder,
One exhaust valve is driven by a fixed cam set to lift characteristics that can avoid exhaust interference with other cylinders,
The other exhaust valve closes on the advance side when the operating angle is smaller than the closing timing of the fixed cam, and closes on the retarded side when the operating angle is larger, or the other exhaust valve operates when the operating angle is smaller than the opening timing of the fixed cam. An internal combustion engine that is driven by a variable cam provided with a variable operating angle mechanism that opens on the retard side and opens on the advanced side when the operating angle is large.

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