JP4151395B2 - High expansion ratio cycle engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a high expansion ratio cycle engine in which an expansion ratio is set larger than a compression ratio.
[0002]
[Prior art]
2. Description of the Related Art Otto-cycle gasoline engines having four strokes (intake, compression, expansion, and exhaust) have been widely used as driving sources for vehicles such as automobiles. In such a gasoline engine, the thermal efficiency is improved by various improvements and devices, but there is a demand for further improving the thermal efficiency.
[0003]
In order to improve thermal efficiency, it is known that the expansion ratio can be increased by extending the stroke when the engine is expanded. However, in the Otto cycle, the piston stroke is the same in each stroke, and the expansion ratio and compression are the same. The ratio is equal. For this reason, when the expansion ratio is increased, the compression ratio is also increased, and the air-fuel mixture is ignited early in the combustion chamber due to the heat generated by the compression, and knocking is likely to occur. Therefore, even if the expansion ratio (= compression ratio) is greatly increased in order to improve the thermal efficiency, the limit is low, and it is difficult to substantially increase the expansion ratio.
[0004]
Therefore, conventionally, the intake amount is limited by greatly advancing the closing timing of the intake valve or delaying the closing timing of the intake valve substantially, and the expansion ratio is substantially reduced by the compression ratio. An engine with a high expansion ratio cycle (hereinafter also referred to as Miller cycle or Atkinson cycle), which is set to be larger than that, has been put into practical use. Moreover, as a technique regarding such a mirror cycle engine, for example, Patent Document 1 and Patent Document 2 disclose the technique.
[0005]
Hereinafter, an engine to which such a mirror cycle is applied will be briefly described with reference to the acupressure diagrams of FIGS. Among these, FIG. 7 is a finger pressure diagram of a so-called intake valve early closing type mirror cycle engine that closes the intake valve at an earlier timing than the piston reaches bottom dead center, and FIG. 8 shows that the piston has reached bottom dead center. It is a shiatsu diagram of a so-called intake valve slow closing type Miller cycle engine which closes an intake valve at a later timing.
[0006]
First, the operation of the intake cycle early closing type mirror cycle engine will be described with reference to FIG. 7. When the piston descends from top dead center (TDC: point a in the figure) and the intake stroke starts, the in-cylinder pressure becomes Intake (or mixture) is taken in from the intake valve while maintaining substantially atmospheric pressure. Then, the intake valve is closed at a predetermined timing (point b in the figure) before the bottom dead center (BDC), thereby completing the substantial intake stroke.
[0007]
Thereafter, the in-cylinder pressure decreases as the piston descends, and the intake stroke ends when the piston reaches bottom dead center (point c in the figure). Then, when the piston reverses upward, the intake stroke shifts to the compression stroke, and the in-cylinder pressure gradually increases as the piston rises. When the piston further rises and the in-cylinder pressure becomes higher than the pressure at the point b (point d in the figure), the substantial compression between the piston stroke position and the top dead center (point e in the figure) at this time The intake air is compressed in the stroke.
[0008]
When the piston reaches the top dead center, the compression stroke ends and the expansion stroke starts. That is, the air-fuel mixture is ignited and combusted in the vicinity of the top dead center of the piston, and the in-cylinder pressure suddenly rises due to the combustion pressure and the piston turns downward (point f in the figure). Then, when the piston reaches the bottom dead center (g point in the figure), it shifts from the expansion stroke to the exhaust stroke, and the combustion gas is discharged at a substantially atmospheric pressure. Further, when the piston reaches top dead center (point a in the figure), a series of mirror cycles is completed, and the intake stroke is started again.
[0009]
In such a mirror cycle of the intake valve early closing type, the intake amount is reduced by closing the intake valve at a timing (point b in the figure) much earlier than the piston reaches the bottom dead center. The compression ratio is greatly reduced.
In addition, since the expansion stroke is from the top dead center to the bottom dead center of the piston as in the past, the expansion stroke is relatively larger than the substantial compression stroke, and thus the expansion ratio ε> the actual compression ratio ρ. be able to. Hereinafter, the actual compression ratio is also referred to as a geometric compression ratio.
[0010]
Thus, by making the expansion ratio ε larger than the geometric compression ratio ρ, it is possible to reduce pump loss (pumping loss) and improve thermal efficiency. Further, knocking (knocking) can be avoided by reducing the compression ratio (for example, compression ratio ρ = 9, ε = 14). However, in such a mirror cycle, the intake amount decreases with respect to the exhaust amount, so the output becomes relatively low. Therefore, conventionally, supercharging (mainly turbocharger) is used to supercharge intake air to ensure output.
[0011]
Such a mirror cycle engine can be realized only by changing the shape of the intake cam as compared with a general Otto cycle engine.
Further, the intake valve slow closing type mirror cycle shown in FIG. 8 also operates in the same manner as the above-described intake valve early closing type except that the intake valve closing timing is different. That is, when the piston descends from top dead center (point a in the figure) and the intake stroke is started, intake (or mixture) is taken in from the intake valve while the in-cylinder pressure is maintained at substantially atmospheric pressure.
[0012]
Even after the piston reaches the bottom dead center (point c in the figure), the state in which the intake valve is opened is maintained, whereby the compression stroke is started while the in-cylinder pressure remains at atmospheric pressure. The intake valve is closed at a predetermined timing after the bottom dead center (point b ′ in the figure), and a substantial compression stroke is started from this point. The subsequent steps are the same as those of the intake valve early closing type.
[0013]
Therefore, like the above-described intake valve early closing type Miller cycle engine, the intake stroke late closing type Miller cycle engine also has a relatively larger expansion stroke than the substantial compression stroke, thereby causing the expansion. Ratio ε> geometric compression ratio ρ.
[0014]
[Patent Document 1]
Japanese Patent Publication No. 7-91984 [Patent Document 2]
Japanese Patent No. 3236654 [0015]
[Problems to be solved by the invention]
By the way, in the conventional mirror cycle engine described above, by setting the expansion ratio to be large, most of the combustion energy in the cylinder can be consumed in the expansion stroke, thereby improving the thermal efficiency. However, as described above, since most of the combustion energy is consumed in the expansion stroke, the energy of the exhaust (that is, the energy for driving the turbocharger, hereinafter referred to as exhaust blowdown energy) is reduced, and the rotational speed of the turbine is reduced. It decreases and the increase speed of supercharging pressure decreases. As a result, the response of the turbocharger is lowered, and there is a problem that the response at the start of the vehicle is deteriorated.
[0016]
In addition, turbochargers generally suffer from a lack of torque due to a decrease in intake air amount until the boost pressure rises during acceleration transients, resulting in poor acceleration. Intake amount is small and the output decreases. In addition to the general characteristics of such a turbocharger, the exhaust blowdown energy is reduced in the Miller cycle engine as described above, so that there is a problem that drivability during acceleration transients and low and medium speed ranges is further deteriorated. .
[0017]
The present invention was devised in view of such a problem, and prevents a decrease in the response of the turbocharger at the time of starting the vehicle and the like, and also prevents a decrease in output at the time of acceleration transient and in a low and medium speed range. An object of the present invention is to provide a high expansion ratio cycle engine.
[0018]
[Means for Solving the Problems]
For this reason, the high expansion ratio cycle engine of the present invention is a high expansion ratio cycle engine in which the expansion ratio is set larger than the compression ratio and the supercharger is provided. If it is determined that the engine is in an acceleration transient when operating at a low load, the control means controls the operation of the variable valve timing mechanism so that the opening timing of the exhaust valve is advanced. As a result, when the vehicle starts, etc., a part of the combustion energy in the cylinder is discharged as exhaust energy before being converted into kinetic energy, and exhaust blowdown energy is increased. And the supercharging efficiency of the intake air by the supercharger is increased by the amount of increase in the exhaust blowdown energy, the response of the supercharger is improved, and the drivability is improved.
Further, at this time, since the operation of the intake side variable valve timing mechanism is controlled so that the intake amount increases, it is possible to prevent a shortage of output torque due to a decrease in the combustion amount. As a result, by canceling the high expansion ratio cycle (mirror cycle) and shifting to a non-high expansion ratio cycle (for example, Otto cycle), sufficient acceleration can be obtained even during acceleration transients and mid to low speed ranges, and drivability is improved. improves.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a high expansion ratio cycle engine according to an embodiment of the present invention will be described with reference to the drawings. The engine 1 shown in FIG. 1 has a high expansion ratio cycle (Miller cycle or Atkinson cycle) in which the expansion ratio is set larger than the compression ratio. In this embodiment, the intake valve early closing type mirror cycle described in the section of the prior art is applied.
[0020]
The engine 1 is a so-called in-cylinder injection type spark ignition engine that supplies fuel directly into a cylinder, and includes fuel injection in an intake stroke (intake stroke injection) and fuel injection in a compression stroke (compression stroke). (Injection) can be switched.
This in-cylinder injection engine 1 is operated at a stoichiometric air fuel ratio (stoichio), an operation at a rich air fuel ratio (rich A / F) (rich air fuel ratio operation), or a lean air fuel ratio (lean A / F). Operation (lean air-fuel ratio operation) is possible, and the above-mentioned plurality of operation modes are switched according to conditions obtained from various parameters.
[0021]
The cylinder head 2 of the engine 1 is provided with a spark plug (not shown) and a fuel injection valve 6 for each cylinder, and a fuel supply device (not shown) is connected to each fuel injection valve 6. ing. This fuel supply apparatus has a low-pressure fuel pump and a high-pressure fuel pump. After the fuel in the fuel tank is pressurized to a low pressure or a high pressure, the fuel is supplied to the fuel injection valve 6.
[0022]
An intake port 9 is formed in the cylinder head 2 in a substantially upright direction for each cylinder, and one end of an intake manifold 10 is connected to the upper end of each intake port 9. As shown in the figure, the intake manifold 10 includes a drive-by-wire throttle valve (ETV) 14 that adjusts the amount of intake air, a throttle position sensor (TPS) 16 that detects the opening of the throttle valve 14, and intake air. An intake air amount sensor (air flow sensor or AFS) 18 for measuring the amount is provided.
[0023]
Here, the ETV 14 includes a throttle actuator 14a, and the throttle opening is changed by the throttle actuator 14a. The operation of the throttle actuator 14a is controlled based on a control signal from an ECU (control means) 40, which will be described later, and usually has a throttle opening corresponding to the depression amount of the accelerator pedal of the driver. Thus, the operation of the throttle actuator 14a is controlled.
[0024]
The cylinder head 2 has an exhaust port 11 for each cylinder, and an exhaust manifold 12 is connected to each exhaust port 11. The exhaust manifold 12 is provided with a turbocharger (supercharger) 13 that pressurizes intake air by exhaust energy. As described in the section of the prior art, this is because the intake amount of the Miller cycle engine decreases with respect to the exhaust amount. The turbocharger 13 secures the intake amount, that is, the output. Although omitted in FIG. 1, a compressor of a turbocharger 13 is interposed on the intake passage 10. In this embodiment, the turbocharger 13 is a so-called variable nozzle vane turbocharger that can change the supercharging pressure by changing the opening of a nozzle vane attached to the turbine.
[0025]
Here, the turbocharger 13 with variable nozzle vanes will be described. As shown in FIG. 3, a plurality of nozzle vanes 13c are arranged at equal intervals around the turbine blade 13b of the turbine 13a. Each nozzle vane 13c is connected to an annular ring 13d disposed coaxially with the turbine 13a. When this annular ring 13d rotates in the direction of the arrow in the figure, the angle of the nozzle vane 13c, that is, the opening degree is changed. It has come to be.
[0026]
An actuator (supercharging pressure changing means) 20 is connected to the annular ring 13d. Here, the actuator 20 is a positive pressure type actuator whose operation state is controlled according to the pressure of the air supplied into the control chamber 20 a, and the angle of the nozzle vane 13 c according to the operation state of the actuator 20. The (opening degree) is adjusted stepwise. Although not shown in detail, the actuator 20 is connected to a high-pressure air passage, and a solenoid valve, for example, is provided on the air passage. The operation of the actuator 20 is controlled by duty-controlling the solenoid valve.
[0027]
The actuator 20 is not limited to such a configuration, and any other configuration may be applied as long as the angle of the nozzle vane can be adjusted continuously or stepwise.
On the other hand, the ECU 40 includes an input / output device, a storage device (ROM, RAM, nonvolatile RAM, etc.), a calculation device (CPU), a timer counter, and the like. Is to be executed.
[0028]
The TPS 16 and AFS 18 described above are connected to the input side of the ECU 40, the engine speed sensor 3 for detecting the engine speed Ne, the accelerator position sensor 4 for detecting the accelerator pedal depression amount Acc of the driver, and the vehicle speed. A vehicle speed sensor 8 is also connected. Further, an O ₂ sensor (not shown), a pressure sensor for detecting the pressure in the intake passage 10 and the like are also connected.
[0029]
On the other hand, various output devices such as the fuel injection valve 6 and the actuator 14a of the ETV (throttle valve) 14 are connected to the output side of the ECU 40, and control signals from the ECU 40 are connected to these output devices. It is designed to be entered. Specifically, in the ECU 40, a target air-fuel ratio (A / F), a target ignition timing, and the like are set based on information from various sensors, and the fuel injection valve 6 is set so as to be the target air-fuel ratio and the target ignition timing. The drive pulse width and the drive amount of the throttle actuator 14a are set.
[0030]
As a result, an appropriate amount of fuel is injected from the fuel injection valve 6 at an appropriate timing, spark ignition is performed at an appropriate timing by the spark plug, and the ETV 14 is driven to open and close at an appropriate opening at an appropriate timing. It has become so.
Next, the main part of the present invention will be described. The valve mechanism of the engine 1 includes an intake side variable valve timing mechanism variable (VVT) 30 capable of changing the operation timing of the intake valve 5 and the operation of the exhaust valve 7. An exhaust side variable valve timing mechanism (VVT) 50 capable of changing the timing is provided.
[0031]
Among them, the intake side VVT 30 is configured to change at least the closing timing of the intake valve 5, and the exhaust side VVT 30 is configured to be able to change at least the opening timing of the exhaust valve. As will be described in detail later, as the VVTs 30 and 50, for example, a known mechanism as shown in FIGS. 2A and 2B is applied.
[0032]
Further, inside the ECU 40, acceleration transient determination means 41 for determining whether or not the engine 1 is in acceleration transient, an operation speed area determination means 42 for determining the operation speed area of the engine 1, and an engine load A load determining means 47 for determining is provided. The acceleration transient determination means 41, the operation speed region determination means 42, and the load determination means 47 constitute an operation state determination means 60 that determines the operation state of the engine 1.
[0033]
Here, the acceleration transient determining means 41 determines whether or not it is during acceleration transient based on the accelerator pedal depression amount Acc detected by the accelerator position sensor 4 and its change amount ΔAcc. When the amount Acc is equal to or greater than the predetermined value a and the accelerator pedal depression amount ΔAcc is equal to or greater than the predetermined value b (≧ 0), the acceleration transient determination means 41 determines that the acceleration is transient. Note that the method for determining whether or not the vehicle is in an acceleration transition is not limited to the above-described method. For example, the engine load such as the intake air amount A / N of the engine 1 or the pressure in the intake passage 10 based on detection information from the AFS 18 is used. You may make it determine based on.
[0034]
Further, the operating speed region determining means 42 determines the operating speed region of the engine 1 based on the engine speed Ne detected by the engine speed sensor 3 and the engine speed is a predetermined speed Ne1. If it is less than this, it is determined that the vehicle is in the low / medium speed region, and if it is greater than or equal to the predetermined rotation speed Ne1, it is determined that it is in the high speed region.
[0035]
The load determining means 47 determines the engine load based on the accelerator pedal depression amount Acc detected by the accelerator position sensor 4 or the intake air amount detected by the AFS 18.
In addition to the above, the ECU 40 is provided with target intake air amount setting means 43, comparison means 44, and supercharging pressure setting means 45. Among these, the target intake air amount setting means 43 sets a target value Vt of the intake air amount of the engine 1 (hereinafter simply referred to as the intake amount) based on the engine speed Ne, the accelerator pedal depression amount (load) Acc, and the like. For example, the target value Vt is read from a map (not shown).
[0036]
The comparison unit 44 compares the target value (target intake air amount) Vt of the intake air amount set by the target intake air amount setting unit 43 with the actual intake air amount (actual intake air amount) Vr detected by the AFS 18. More specifically, a difference ΔV (= Vr−Vt) between the actual intake air amount Vr and the target intake air amount Vt is calculated.
The supercharging pressure setting means 45 sets the supercharging pressure of the turbocharger 13, and the supercharging pressure of the actuator 20 of the turbocharger 13 is set so as to be the supercharging pressure set by the supercharging pressure setting means 45. The operation is feedback controlled.
[0037]
Then, it is determined by the operating speed region determining means 42 that the engine 1 is operating in the low / medium speed region, and it is determined by the load determining means 47 that the engine 1 is operating in the low load region, and during acceleration transient When it is determined by the determination means 41 that the operating state of the engine 1 is during acceleration transient, the following exhaust blowdown energy improvement control is executed.
[0038]
In other words, in this case, the actual intake air amount Vr is compared with the actual intake air amount Vr detected by the AFS 18 by comparing the intake air amount Vt set by the target intake air amount setting unit 43 with the comparison unit 44. If it is determined that it is Vt or less (if ΔV ≦ 0), it is determined that the intake air amount is insufficient (that is, the output is insufficient), and the ECU 40 increases the exhaust blowdown energy. A control signal for advancing the opening timing of the exhaust valve 7 with respect to the exhaust side VVT 50 is output.
[0039]
That is, as described above, in the Miller cycle engine, by setting the expansion ratio to be large, most of the combustion energy can be consumed in the expansion stroke to improve the thermal efficiency, but the combustion energy is almost consumed in the expansion stroke. Therefore, the exhaust blowdown energy for driving the turbocharger 13 is reduced. As a result, the response of the turbocharger 13 is lowered, and drivability is deteriorated. In particular, when the engine 1 is accelerated from a low load range or a low / medium speed range (for example, at the time of starting), the intake amount is small and the output is reduced, so that drivability is further deteriorated.
[0040]
Therefore, as described above, when it is determined that the operating state of the engine 1 is in the low / medium speed region and the low load region and is in the acceleration transient state, the exhaust side VVT 50 is operated to open the exhaust valve 7. The timing has been advanced. As a result, the exhaust valve 7 opens in the vicinity of the bottom dead center of the piston in the latter half of the expansion stroke during normal operation, whereas the exhaust valve 7 opens earlier than normal during the expansion stroke when the VVT 50 is operated. Energy can be supplied to the turbocharger 13 as exhaust blowdown energy. As a result, the supercharging pressure of the turbocharger 13 is quickly increased, the response of the turbocharger 13 is improved, and drivability can be improved when starting.
[0041]
Further, the control of the intake side VVT 30 is also executed independently of the control of the exhaust side VVT 50 as described above. Specifically, it is determined by the acceleration transient determination means 41 that the operating state of the engine 1 is an acceleration transient, or the operation speed area determination means 42 determines that the engine is operating in the middle / low speed range. Then, the ECU 40 is configured to output a control signal so as to retard the closing timing of the intake valve 5 with respect to the VVT 30 in order to compensate for the intake amount deficient in the engine 1.
[0042]
This is mainly due to the following reasons. In other words, in the intake cycle early closing type mirror cycle engine in this embodiment, the intake amount is reduced by closing the intake valve 5 at a timing much earlier than the piston reaches the bottom dead center during the intake stroke. The mirror cycle is realized by the ratio ε> the actual compression ratio (geometric compression ratio) ρ.
[0043]
And by making the expansion ratio ε larger than the geometric compression ratio ρ in this way, the pump loss is reduced to improve the thermal efficiency, and knocking (for example, the compression ratio ρ = 9) is knocked ( Knock) is avoided. However, in such a mirror cycle, since the intake air amount decreases with respect to the exhaust gas amount, the output becomes relatively low. Therefore, as described above, the turbocharger 13 supercharges the intake air to ensure the output. .
[0044]
However, the turbocharger 13 generally has a time lag between when the accelerator is depressed and when supercharging is performed. The same applies to a so-called supercharger that extracts driving force from the crankshaft and compresses intake air. For this reason, during the acceleration transition, the intake air amount is insufficient until the boost pressure rises, resulting in acceleration failure. In the Miller cycle, the lower the compression ratio and the higher the expansion ratio, the higher the thermal efficiency. However, if the compression ratio is too low, the intake air amount is low and the output is low when the supercharging pressure in the low and medium speed ranges is low. There is a risk of lowering.
[0045]
Therefore, as described above, when it is determined that the operating state of the engine 1 is in an acceleration transition state or the engine 1 is operating in the low / medium speed range, the VVT 30 is operated to close the intake valve 5. By retarding the angle, the intake stroke is substantially increased to compensate for the insufficient intake amount. When the closing timing of the intake valve 5 is retarded, the closing timing is at the vicinity of the bottom dead center at the maximum.
[0046]
Next, an example of the configuration of the VVTs 30 and 50 will be briefly described with reference to FIGS. Note that the VVTs 30 and 50 are configured in the same manner, and therefore, the VVT 30 on the intake side will be described as an example here. The VVT 30 includes cams 32a and 32b that are formed on the camshaft 31 and rotate corresponding to the rotation of the crankshaft, and rocker arms 33a and 33b that are driven by the cams 32a and 32b. Both of these rocker arms 33a and 33b do not contact the intake valves 5 and 5, and are configured as sub-rocker arms indirectly related to the opening and closing drive of the intake valves 5 and 5. Between these sub rocker arms 33a and 33b, there is provided a main rocker arm 33c which is in contact with the stem end portion of the intake valves 5 and 5 and directly related to the opening and closing drive of the intake valves 5 and 5.
[0047]
Further, one cam 32a has a cam profile suitable for a mirror cycle for early intake closing, and the other cam 32b has a cam profile that retards the valve closing timing than the one cam 32a. ing.
Here, the main rocker arm 33 c is formed integrally with the rocker shaft 34 and is configured to be swingable together with the rocker shaft 34. The tip of the main rocker arm 33c is in contact with the stem upper end of the intake valves 5 and 5.
[0048]
Further, the two sub rocker arms 33a and 33b are pivotally supported so as to be rotatable relative to the rocker shaft 34 (that is, the main rocker arm 33c).
Further, as shown in FIG. 2B, between the sub rocker arms 33a and 33b and the rocker shaft 34, the sub rocker arms 33a and 33b are rotatable with respect to the rocker shaft 34, and the main rocker arm 33c and Hydraulic piston mechanisms 36a and 36b are provided that can switch between a mode in which no linkage operation is performed (non-linkage mode) and a mode in which the sub-rocker arms 33a and 33b rotate integrally with the rocker shaft 34 and link with the main rocker arm 33c (linkage mode). ing.
[0049]
In addition, oil passages 34a and 34b are formed inside the rocker shaft 34, and the operation of the hydraulic piston mechanisms 36a and 36b is switched by the hydraulic oil supplied and discharged from the oil passages 34a and 34b. ing. For example, when hydraulic fluid is supplied from the oil passages 34a and 34b to the piston mechanisms 36a and 36b, the piston 37a is driven to the base end side in the piston mechanism 36a, and the tip of the piston 37a is detached from the hole 38a. On the other hand, in the piston mechanism 36b, the piston 37b is driven to the tip end side, and the tip end portion of the piston 37b is fitted into the hole 38b.
[0050]
When the piston 37b is inserted into the hole 38b, the sub rocker arm 33b rotates integrally with the rocker shaft 34 to be linked to the main rocker arm 33c (linkage mode), and the piston 37a is detached from the hole 38a. The rocker arm 33a is rotatable with respect to the rocker shaft 34, and is in a mode in which the rocker arm 33a is not linked to the main rocker arm 33c (non-linked mode).
[0051]
Further, the supply state of the above-described hydraulic oil is controlled by the ECU 40, thereby appropriately switching between the linkage mode and the non-linkage mode of the sub rocker arms 33b and 33a, and the closing timing of the intake valve 5 is set. Can be changed.
Since the high expansion ratio cycle engine according to the embodiment of the present invention is configured as described above, the intake-side VVT 30 is controlled according to a flowchart as shown in FIG. 4, for example. First, in step S1, information from each sensor is captured. Specifically, the engine speed Ne obtained from the engine speed sensor 3 and the accelerator opening degree Acc obtained from the accelerator position sensor 4 are taken in. Next, in step S2, based on the engine speed Ne and the accelerator opening Acc, it is determined whether the engine 1 is operating in the low / medium speed range or at the time of acceleration transient. In addition, you may determine whether it is at the time of acceleration transition based on A / N as an engine load, or intake pressure.
[0052]
If it is determined in step S2 that the engine 1 is operating in the low / medium speed range or is in an acceleration transient state, the process proceeds to step S3, where the actual intake air amount is compared with the target intake air amount. If the amount is less than or equal to the target intake air amount, the process proceeds to step S4, and the closing timing of the intake valve 5 is controlled to the retard side.
On the other hand, the operation of the exhaust side VVT 50 is controlled based on, for example, a flowchart as shown in FIG. First, in step S11, information from each sensor is captured. Next, in step S12, it is determined with reference to the various types of information captured in step S11 whether or not it is an acceleration transient during low-medium speed and low-load operation.
[0053]
If the acceleration is transient during low-medium speed and low-load operation, it is considered that the intake air amount has decreased due to a decrease in the exhaust blowdown energy. Therefore, in step S13, the actual intake air amount Vr and the target intake air amount Vt. Are compared, and when it is determined that the actual intake air amount Vr is equal to or less than the target intake air amount Vt, the routine proceeds to step S14, where the valve opening timing of the exhaust valve 7 is controlled to the advance side. That is, in this case, in order to increase the exhaust blowdown energy, the exhaust valve 7 is opened earlier than during normal operation, and the exhaust energy is supplied to the turbocharger 13. Thereby, the supercharging pressure can be quickly increased, and the response of the turbocharger 13 is improved. Note that if it is determined in step S12 that the acceleration is not transient during low-medium speed and low-load operation, the process directly returns.
[0054]
Therefore, according to the high expansion ratio cycle engine according to an embodiment of the present invention, when the exhaust blowdown energy is low, such as when the vehicle starts, the exhaust valve 7 is temporarily advanced to advance the exhaust timing. Blowdown energy can be increased. Therefore, the supercharging pressure can be quickly increased, and the response of the turbocharger 13 is improved. As a result, drivability is improved.
[0055]
Further, when the intake air amount until the boost pressure rises at the time of acceleration transition is small, the closing timing of the intake valve 5 is retarded (high compression ratio) so that the intake air amount increases. The shortage of output torque due to the decrease in the amount is resolved, and sufficient acceleration can be obtained. In the low and medium speed range, the supercharging pressure is low and the intake amount is still insufficient, but the closing timing of the intake valve 5 is retarded (high compression ratio) so that the intake amount increases as described above. Thus, there is an advantage that deficiency in output torque due to a decrease in combustion amount can be solved and drivability is improved. Moreover, since the technology of the variable valve timing mechanism which has already been put into practical use can be applied, there is an advantage that the mechanical reliability is high.
[0056]
In addition, this invention is not limited to the thing of the above-mentioned embodiment. For example, in the above-described embodiment, the case of applying the inspiratory early closing type mirror cycle has been described, but the inspiratory late closing type mirror cycle (see the acupressure diagram in FIG. 8) may be applied to the present invention.
Further, the VVT (variable valve timing mechanism) is not limited to the rocker arm switching type as described above, and various other mechanisms can be applied as long as the closing timing of the intake valve 5 can be changed. is there. For example, as the variable valve timing mechanism, an electromagnetic intake valve in which the opening / closing timing and the lift amount can be arbitrarily set by the driving force of the electromagnetic coils 5a and 5b as shown in FIG. 6 may be applied.
[0057]
Needless to say, the engine to which the present invention is applied is not limited to the in-cylinder injection type spark ignition engine as described above, but can be applied to a port injection type engine.
In the above-described embodiment, it is determined whether or not the intake air amount is the target intake air amount using information from the AFS (air flow sensor), but a pressure sensor (boost pressure sensor) is disposed downstream of the turbocharger. ) To determine whether the actual intake air pressure is larger than the target intake air pressure based on the boost pressure obtained by the pressure sensor, and thereby determine whether the intake air amount is less than the target value. Good.
[0058]
【The invention's effect】
As described above in detail, according to the high expansion ratio cycle engine of the present invention, for example, when the vehicle starts, the engine operating range is a low / medium speed range and a low load range, and the engine is in an acceleration transient state. If so, the operation of the variable valve timing mechanism is controlled so that the opening timing of the exhaust valve is advanced, so that the exhaust blowdown energy increases and the supercharging pressure rises quickly. Thereby, the response of the supercharger is improved, and drivability at the time of starting is improved. Moreover, since already it can be applied technology of the variable valve timing mechanism that has been put to practical use, Ru mower advantage high mechanical reliability.
In addition, during the acceleration transition and in the operation range where the supercharging pressure in the medium / low speed range is low, the intake valve closing timing is controlled so that the intake amount increases, so that it is possible to prevent shortage of output torque due to a decrease in the combustion amount. . Accordingly, the acceleration obtain sufficient acceleration in transient or medium or low speed region, an advantage there Ru that drivability is improved.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing the overall configuration of a high expansion ratio cycle engine according to an embodiment of the present invention.
FIGS. 2A and 2B are schematic cross-sectional views for explaining an example of a variable valve timing mechanism applied to a high expansion ratio cycle engine according to an embodiment of the present invention.
FIG. 3 is a schematic diagram showing a supercharger of the high expansion ratio cycle engine according to the first embodiment of the present invention.
FIG. 4 is a flowchart illustrating the operation of the high expansion ratio cycle engine according to the first embodiment of the present invention.
FIG. 5 is a flowchart illustrating the operation of the high expansion ratio cycle engine according to the first embodiment of the present invention.
FIG. 6 is a schematic diagram for explaining another example of the variable valve timing mechanism applied to the present invention.
FIG. 7 is an acupressure diagram illustrating an example of a conventional high expansion ratio cycle engine.
FIG. 8 is a shiatsu diagram illustrating another example of a conventional high expansion ratio cycle engine.
[Explanation of symbols]
1 Engine 5 Intake valve 7 Exhaust valve 13 Turbocharger (supercharger)
14 ETV (drive-by-wire slot valve)
30 VVT (Intake side variable valve timing mechanism)
40 ECU (control means)
41 Acceleration transient determination means 42 Operating speed region determination means 50 VVT (exhaust side variable valve timing mechanism)
60 Operating state determination means

Claims (1)

In a high expansion ratio cycle engine with an expansion ratio set larger than the compression ratio and a supercharger,
An operating state determining means for determining the operating state of the engine;
An exhaust side variable valve timing mechanism capable of changing the opening timing of the exhaust valve of the engine;
An intake side variable valve timing mechanism capable of changing the closing timing of the intake valve of the engine;
Control means for controlling the operation of the two variable valve timing mechanisms;
When it is determined by the operating state determination means that the engine is operated in a low / medium speed range and a low load range and the engine is in an acceleration transient state, the opening timing of the exhaust valve is determined by the control means. advancing operation of the variable valve timing mechanism is controlled so as to Rutotomoni, actuation of the intake-side variable valve timing mechanism so that the amount of intake air is increased by the control means is controlled to stop the expansion ratio cycle And a high expansion ratio cycle engine, wherein the engine is shifted to a non-high expansion ratio cycle .

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