JP2004183512A - High expansion ratio cycle engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a lowering of output by increasing the intake air quantity in the accelerating transition and low-medium speed range of a high expansion ratio cycle engine. <P>SOLUTION: In the high expansion ratio cycle engine 1 provided with a supercharger 13, when the engine is determined to be in the accelerating transition by an accelerating transition determining means 41, the operation of a variable valve timing mechanism 30 is controlled to increase the intake air quantity. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a high expansion ratio cycle engine in which an expansion ratio is set to be larger than a compression ratio.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an Otto cycle gasoline engine having four strokes of intake, compression, expansion, and exhaust has been widely used as a drive source of a vehicle such as an automobile. In such a gasoline engine, the thermal efficiency has been improved by various improvements and ideas, but there is a demand for further improving the thermal efficiency.
[0003]
It is known that thermal efficiency can be improved by increasing the expansion stroke of the engine and increasing the expansion ratio.However, in the Otto cycle, the piston stroke in each stroke is the same, and the expansion ratio and the compression ratio are increased. Is equal to the ratio. 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 heat generated by the compression, and knocking easily occurs. Therefore, even if the expansion ratio (= compression ratio) is greatly increased in order to improve the thermal efficiency, it is difficult to substantially increase the expansion ratio because the limit is low.
[0004]
Therefore, conventionally, the amount of intake air is limited by greatly advancing the closing timing of the intake valve or greatly retarding the closing timing of the intake valve, thereby substantially reducing the expansion ratio and the compression ratio. An engine having a high expansion ratio cycle (hereinafter, also referred to as a Miller cycle or an Atkinson cycle), which is set to be larger than that, has been put to practical use. Further, a technique relating to such a Miller cycle engine is also disclosed in, for example, Patent Documents 1 and 2.
Hereinafter, an engine to which such a Miller cycle is applied will be briefly described with reference to the acupressure diagrams of FIGS. 6 and 7. Among them, FIG. 6 is a finger pressure diagram of a so-called intake valve early-closing type Miller cycle engine in which the intake valve is closed earlier than the piston reaches the bottom dead center, and FIG. 7 is the piston reaches the bottom dead center. FIG. 7 is a diagram of acupressure of a so-called intake valve late closing type Miller cycle engine in which an intake valve is closed at a later timing.
[0005]
First, the operation of the Miller cycle engine of the intake valve early closing type will be described with reference to FIG. 6. When the piston descends from top dead center (TDC: point a in the figure) to start the intake stroke, the in-cylinder pressure becomes The intake air (or air-fuel mixture) is taken in from the intake valve while maintaining substantially the atmospheric pressure. Then, at a predetermined timing (point b in the drawing) just before the bottom dead center (BDC), the intake valve is closed, thereby ending the substantial intake stroke.
[0006]
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 is reversed to rise, the process shifts from the intake stroke to the compression stroke, and the in-cylinder pressure gradually increases with the rise of the piston. Further, when the piston rises and the in-cylinder pressure becomes higher than the pressure at point b (point d in the figure), a substantial compression from the stroke position of the piston at this time to the top dead center (point e in the figure) is performed. In the process, intake air compression is performed.
[0007]
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 burned near the top dead center of the piston, and the in-cylinder pressure is rapidly increased by the combustion pressure and the piston is turned downward (point f in the figure). When the piston reaches the bottom dead center (point g in the figure), the process shifts from the expansion stroke to the exhaust stroke, and the combustion gas is exhausted at substantially atmospheric pressure. Further, when the piston reaches the top dead center (point a in the figure), a series of Miller cycles ends, and the intake stroke is started again.
[0008]
In such a mirror cycle of the intake valve early closing type, the intake air amount is reduced by closing the intake valve at a timing (point b in the drawing) much earlier than the piston reaches the bottom dead center. Greatly decreases the compression ratio.
Further, since the expansion stroke is from the top dead center to the bottom dead center of the piston as before, the expansion stroke becomes relatively larger than the substantial compression stroke, whereby 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.
[0009]
By making the expansion ratio ε larger than the geometric compression ratio ρ, the pump loss (pumping loss) is reduced and the thermal efficiency is improved. Further, knocking (knock) can be avoided by reducing the compression ratio (for example, compression ratio ρ = 9, ε = 14). However, in such a mirror cycle, the output is relatively low because the intake amount is reduced with respect to the exhaust amount. Therefore, conventionally, the output is secured by supercharging the intake air with a supercharger.
[0010]
It should be noted that such a Miller cycle engine can be realized only by changing the shape of the intake cam with respect to a general Otto cycle engine.
Also, the intake valve late closing type mirror cycle shown in FIG. 7 operates similarly to the above-described intake valve early closing type except that the closing timing of the intake valve is different. That is, when the piston descends from the top dead center (point a in the figure) and the intake stroke is started, the intake air (or air-fuel mixture) is taken in from the intake valve while the in-cylinder pressure keeps substantially the atmospheric pressure.
[0011]
Then, even after the piston reaches the bottom dead center (point c in the figure), the intake valve is kept open so that the compression stroke is started with the in-cylinder pressure at atmospheric pressure. Then, at a predetermined timing after the bottom dead center (point b 'in the figure), the intake valve is closed, 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.
[0012]
Therefore, similarly to the above-described intake valve early closing type mirror cycle engine, the expansion stroke of the intake valve late closing type mirror cycle engine is relatively larger than the substantial compression stroke, thereby increasing the expansion stroke. Ratio ε> geometric compression ratio ρ.
[0013]
[Patent Document 1]
Japanese Patent Publication No. 7-91984 [Patent Document 2]
Japanese Patent No. 3236654
[Problems to be solved by the invention]
By the way, as described above, in the Miller cycle engine, intake air is supercharged by a supercharger because the intake air amount is reduced with respect to the exhaust gas amount. However, such a conventional technique has the following problems. Was.
That is, the supercharger generally has a time lag between when the accelerator is depressed and when supercharging is performed. For this reason, during the transition of acceleration, the intake air amount is reduced until the boost pressure rises, and as a result, the torque becomes insufficient and acceleration failure occurs. In the Miller cycle, the thermal efficiency increases as the compression ratio and the expansion ratio increase, but if the compression ratio is too low, the intake air volume will be small in the low and medium speed range where the supercharging pressure is low. There is a risk of lowering.
[0015]
SUMMARY OF THE INVENTION The present invention has been made in view of such a problem, and has a high expansion ratio in which the intake air amount is increased at the time of transient acceleration or when the supercharging pressure is reduced in a low-to-medium-speed region to prevent a decrease in output. The purpose is to provide a cycle engine.
[0016]
[Means for Solving the Problems]
Therefore, in the high expansion ratio cycle engine according to the present invention, in the high expansion ratio cycle engine having the expansion ratio set to be larger than the compression ratio and having the supercharger, the engine operation is performed by the acceleration transient determination means. If it is determined that the state is during transient acceleration, the operation of the variable valve timing mechanism is controlled by the control means so that the intake air amount increases.
[0017]
According to a second aspect of the present invention, there is provided a high expansion ratio cycle engine according to the present invention, wherein the expansion ratio is set to be larger than the compression ratio, and the operation speed of the engine is determined by the operation speed region determining means. When it is determined that the speed region is the low-medium speed region, the operation of the variable valve timing mechanism is controlled by the control means so that the intake air amount increases.
[0018]
In this case, in the case of a high-expansion-ratio cycle engine of the early-closed-valve type in which the expansion ratio is made larger than the compression ratio by closing the intake valve during the intake stroke, the closing of the intake valve is performed. The intake air amount is increased by retarding the timing. Further, in the case of a high-expansion-ratio cycle engine of a late-closing type in which the intake valve is closed during the compression stroke so that the expansion ratio becomes larger than the compression ratio, the closing timing of the intake valve Is advanced to increase the intake air amount.
[0019]
Furthermore, during operation in a low to medium load range, the opening of the throttle valve is set to be larger than the driver's required opening based on the accelerator pedal depression amount to compensate for the decrease in intake air amount, further reducing intake pump loss. You.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the high expansion ratio cycle engine according to the first 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 engine) in which the expansion ratio is set larger than the compression ratio. In the first embodiment, the Miller cycle of the intake valve early closing type described in the section of the related art is applied.
[0021]
The engine 1 is a so-called in-cylinder injection type spark ignition engine that supplies fuel directly into a cylinder, and performs fuel injection in an intake stroke (intake stroke injection) and fuel injection in a compression stroke (compression stroke). (Injection).
The in-cylinder injection type engine 1 operates at a stoichiometric air-fuel ratio (stoichio), at an rich air-fuel ratio (rich A / F) (rich air-fuel ratio operation), or at a lean air-fuel ratio (lean A / F). Operation (lean air-fuel ratio operation) is possible, and the plurality of operation modes described above are switched according to conditions obtained from various parameters.
[0022]
Further, an ignition plug (not shown) and a fuel injection valve 6 are provided for each cylinder in the cylinder head 2 of the engine 1, and a fuel supply device (not shown) is connected to each fuel injection valve 6. ing. This fuel supply device 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.
[0023]
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 an upper end of each intake port 9. As shown, the intake manifold 10 has a drive-by-wire type throttle valve (ETV) 14 for adjusting the intake air amount, a throttle position sensor (TPS) 16 for detecting the opening degree of the throttle valve 14, and an intake air An intake air amount sensor (air flow sensor or AFS) 18 for measuring the amount is provided.
[0024]
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 amount of depression of the accelerator pedal by the driver. Thus, the operation of the throttle actuator 14a is controlled.
[0025]
An exhaust port 11 is formed in the cylinder head 2 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 with exhaust energy. This is because, as described in the section of the prior art, in the Miller cycle engine, the intake amount is reduced with respect to the exhaust amount, and the turbocharger 13 secures the intake amount, that is, the output. Although not shown in FIG. 1, a compressor of the turbocharger 13 is provided on the intake passage 10.
[0026]
On the other hand, the ECU 40 includes an input / output device, a storage device (ROM, RAM, non-volatile RAM, etc.), a computing device (CPU), a timer counter, and the like. Is to be executed. The input side of the ECU 40 is connected to the TPS 16 and the intake air amount sensor 18 described above, and also connected to the engine speed sensor 3 for detecting the engine speed Ne and the accelerator position sensor 4 for detecting the accelerator pedal depression amount Acc of the driver. Have been. Furthermore, also connected a pressure sensor for detecting the pressure of the O ₂ sensor and the intake passage 10 (not shown).
[0027]
On the other hand, on the output side of the ECU 40, various output devices such as the above-described fuel injection valve 6 and the actuator 14a of the ETV (throttle valve) 14 are connected. These output devices receive control signals from the ECU 40. Is to be entered. Specifically, the ECU 40 sets a target air-fuel ratio (A / F), a target ignition timing, and the like based on information from various sensors, and sets the fuel injection valve 6 so that the target air-fuel ratio and the target ignition timing are obtained. And the drive amount of the throttle actuator 14a are set.
[0028]
Then, 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 a spark plug, and the ETV 14 is opened and closed so as to have an appropriate opening at an appropriate timing. It has become so.
Next, the main part of the present invention will be described. The variable valve timing mechanism (VVT) 30 which can change the operation timing of the intake valve 5 is provided in the valve mechanism on the intake valve side of the engine 1. . The VVT 30 is configured so that at least the closing timing of the intake valve 5 can be changed, and will be described in detail later. For example, a known VVT 30 as shown in FIGS. 2A and 2B is applied. I have.
[0029]
Further, inside the ECU 40, an acceleration transition time determination unit 41 that determines whether the engine 1 is in an acceleration transition state based on an operation state of the engine 1, an operation speed region determination unit that determines an operation speed region of the engine 1 42 and target intake air amount setting means 43 for setting a target value of the intake air amount.
Here, the acceleration transient determination means 41 determines whether or not the vehicle is in an acceleration transition based on the accelerator pedal depression amount Acc detected by the accelerator position sensor 4 and the variation ΔAcc. When the amount Acc is equal to or greater than a predetermined value a and the accelerator pedal depression change amount ΔAcc is equal to or greater than a predetermined value b (≧ 0), the acceleration transition determination unit 41 determines that the vehicle is in the acceleration transition. It should be noted that the method of determining whether or not the time is during the 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 the detection information from the AFS 18 is determined. The determination may be made based on this.
[0030]
The operating speed range determining means 42 determines the operating speed range of the engine 1 based on the engine speed Ne detected by the engine speed sensor 3 at 3, and when the engine speed is equal to the predetermined speed Ne 1. If it is less than the predetermined rotational speed Ne1, it is determined that the vehicle is in the high speed region.
[0031]
Further, the target intake air amount setting means 43 sets a target value Vt of the intake air amount (hereinafter, simply referred to as an intake amount) of the engine 1 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).
Then, it is determined by the transient acceleration determination means 41 that the operating state of the engine 1 is in the transient acceleration state, or it is determined by the operating speed region determining means 42 that the engine is operating in the low to medium speed range, and By comparing the intake air amount Vt set by the target intake air amount setting means 43 with the actual intake air amount Vr detected by the AFS 18, if it is determined that the actual intake air amount Vr is equal to or smaller than the target intake air amount Vt, the intake air When it is determined that the air amount is insufficient, the ECU 40 outputs a control signal to the VVT 30 so as to retard the closing timing of the intake valve 5 to the VVT 30 so as to compensate for the insufficient intake air amount in the engine 1. I have.
[0032]
That is, as described above, in the Miller cycle engine of the intake valve early closing type in this embodiment, the intake amount is reduced by closing the intake valve 5 at a timing significantly earlier than the time when the piston reaches the bottom dead center during the intake stroke. Thus, a Miller cycle is realized with the expansion ratio ε> the actual compression ratio (geometric compression ratio) ρ.
By making the expansion ratio ε larger than the geometric compression ratio ρ, the pump loss is reduced and the thermal efficiency is improved, and knocking (for example, compression ratio ρ = 9) is achieved by lowering the compression ratio (for example, compression ratio ρ = 9). Knocks) have been avoided. However, in such a Miller cycle, since the intake amount is reduced with respect to the exhaust amount, the output is relatively low. Therefore, as described above, the intake is supercharged by the turbocharger 13 to secure the output. .
[0033]
However, the turbocharger 13 generally has a time lag between when the accelerator is depressed and when supercharging is performed. This is the same with a so-called supercharger that extracts the driving force from the crankshaft and compresses the intake air. For this reason, at the time of acceleration transition, the intake air amount becomes insufficient until the boost pressure rises, and poor acceleration occurs. In the Miller cycle, the thermal efficiency increases as the compression ratio and the expansion ratio increase, but if the compression ratio is too low, the intake air volume will be small in the low and medium speed range where the supercharging pressure is low. There is a risk of lowering.
[0034]
Therefore, as described above, it is determined that the operation state of the engine 1 is in the transition to acceleration, or that the engine 1 is operating in the low-medium speed range, and that the actual intake air amount is equal to or less than the target intake air amount. Then, by operating the VVT 30 to retard the closing timing of the intake valve 5, the intake stroke is substantially increased to compensate for the insufficient intake air amount. When the valve closing timing of the intake valve 5 is retarded, the valve closing timing is at most near the bottom dead center.
[0035]
Next, an example of the configuration of the VVT 30 will be briefly described with reference to FIGS. 2A and 2B. The VVT 30 is a cam 32a formed on a camshaft 31 and rotated in response to rotation of a crankshaft. , 32b and rocker arms 33a, 33b driven by these cams 32a, 32b. These rocker arms 33a and 33b do not abut against the intake valves 5 and 5, but are configured as sub rocker arms that are indirectly involved in opening and closing the intake valves 5 and 5. A main rocker arm 33c is provided between the sub rocker arms 33a and 33b and abuts on the stem ends of the intake valves 5 and 5 and is directly involved in opening and closing the intake valves 5 and 5.
[0036]
Further, one cam 32a has a cam profile suitable for a mirror cycle of early closing intake, and the other cam 32b has a cam profile that retards the valve closing timing more than the one cam 32a. ing.
Here, the main rocker arm 33c 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 upper end of the stem of each of the intake valves 5 and 5.
[0037]
Each of the two sub rocker arms 33a and 33b is rotatably supported relative to the rocker shaft 34 (that is, the main rocker arm 33c).
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 are connected to the main rocker arm 33c. Hydraulic piston mechanisms 36a and 36b are provided which can switch between a mode in which no link 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 perform a link operation with the main rocker arm 33c (linkage mode). ing.
[0038]
Further, oil passages 34a and 34b are formed inside the rocker shaft 34, and the operation of the hydraulic piston mechanisms 36a and 36b can be switched by hydraulic oil supplied and discharged from the oil passages 34a and 34b. ing. For example, when hydraulic oil is supplied to each of the piston mechanisms 36a and 36b from the oil passages 34a and 34b, the piston 37a of the piston mechanism 36a is driven toward the base end so that the distal end of the piston 37a is separated from the hole 38a. On the other hand, in the piston mechanism 36b, the piston 37b is driven toward the distal end, and the distal end of the piston 37b fits into the hole 38b.
[0039]
When the piston 37b is fitted into the hole 38b, the sub rocker arm 33b rotates integrally with the rocker shaft 34 to be in a mode in which the sub rocker arm 33b operates in cooperation with the main rocker arm 33c (coupling mode). The rocker arm 33a is rotatable with respect to the rocker shaft 34, and is in a mode in which the rocker arm 33a does not operate in cooperation with the main rocker arm 33c (non-coupling mode).
[0040]
Further, the supply state of the above-mentioned hydraulic oil is controlled by the ECU 40, whereby the interlocking mode and the non-interlocking mode of the sub rocker arms 33b and 33a are appropriately switched to set the valve closing timing of the intake valve 5. Can be changed.
Since the high expansion ratio cycle engine according to the first embodiment of the present invention is configured as described above, the ECU 40 controls the engine 1 based on information from the engine speed sensor 3 and the accelerator position sensor 4 when the engine 1 is in an acceleration transition. In a state in which the sub-rocker arm 33a is operating in a high-speed range, the sub-rocker arm 33a is switched to a mode in which the sub-rocker arm 33a operates in cooperation with the main rocker arm 33c.
[0041]
Therefore, in this case, the intake valve 5 is driven to be opened and closed by the cam 32a having a cam profile suitable for the Miller cycle of early intake closing. Specifically, when the piston descends from top dead center and the intake stroke starts, the intake valve opens and intake air is taken in from the intake valve. Then, at a predetermined timing before the bottom dead center (BDC) (see point b in FIG. 6), the intake valve 5 is closed, whereby the substantial intake stroke ends.
[0042]
By closing the intake valve 5 at a timing substantially earlier than the time when the piston reaches the bottom dead center, the amount of intake air is reduced, whereby the compression ratio is reduced. In addition, since the expansion stroke is from the top dead center to the bottom dead center of the piston as before, the expansion stroke is relatively larger than the substantial compression stroke, whereby the expansion ratio ε> the geometric compression ratio ρ. In addition, the pump efficiency is reduced and the thermal efficiency is improved. In addition, knocking (knock) can be avoided by lowering the compression ratio (for example, compression ratio ρ = 9).
[0043]
On the other hand, based on information from the engine speed sensor 3 and the accelerator position sensor 4, the ECU 40 determines that the engine 1 is in the transition of acceleration or is operating in a low to medium speed range, and the actual intake air amount is equal to the target intake air amount. If it is determined that the amount is equal to or less than the amount, the link operation between the sub rocker arm 33a and the main rocker arm 33c is released, and the mode is switched to the mode in which the other sub rocker arm 33b operates in cooperation with the main rocker arm 33c.
[0044]
Therefore, in this case, the intake valve 5 is driven to be opened and closed by the cam 32b whose valve closing timing is set to a more retarded side than the Miller cycle of early intake closing. In other words, in this case, when the piston descends from the top dead center and the intake stroke starts, the intake valve opens and passes a predetermined timing before the bottom dead center (BDC) (see point b in FIG. 6). Even so, the intake valve 5 is maintained in the open state. Then, near the bottom dead center, the intake valve 5 is closed, and a large amount of intake air flows into the cylinder by an amount corresponding to the retarded valve closing timing.
[0045]
As a result, it is possible to secure insufficient intake air at the time of low / medium speed or transition of acceleration, and it is possible to prevent a decrease in output torque.
Hereinafter, the operation of the present invention will be described with reference to the flowchart of FIG. 3. First, in step S1, information from each sensor is taken in. Specifically, the engine speed Ne obtained from the engine speed sensor 3 and the accelerator opening 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 a low-medium speed range or during acceleration transition. Note that whether or not the vehicle is in the transition to acceleration may be determined based on the A / N or the intake pressure as the engine load.
[0046]
If it is determined in step S2 that the engine 1 is operating in the low-medium speed range or that the engine is in a 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 equal to or less than the target intake amount, the process proceeds to step S4, and the closing timing of the intake valve 5 is controlled to the retard side.
Therefore, according to the high expansion ratio cycle engine according to the first embodiment of the present invention, when the intake air amount is small until the boost pressure rises during the acceleration transition, the intake valve increases so that the intake air amount increases. Since the valve closing timing of No. 5 is retarded (higher compression ratio), the output torque shortage due to the decrease in the combustion amount is eliminated, and sufficient acceleration can be obtained. In addition, although the supercharging pressure is low and the intake air amount tends to be insufficient in the low to medium speed range, the closing timing of the intake valve 5 is retarded (to increase the compression ratio) so that the intake air amount increases as described above. Thus, there is an advantage that output torque shortage due to a decrease in the amount of combustion can be resolved and drivability is improved. In addition, since the technology of the variable valve timing mechanism that has already been put to practical use can be applied, there is an advantage that mechanical reliability is high.
[0047]
Next, a second embodiment of the present invention will be described. Since the second embodiment has the same basic configuration as the first embodiment, the second embodiment will be described with reference to FIG.
In the second embodiment, in addition to the configuration of the first embodiment, when the engine 1 is operated in a low to middle load range, the ECU 40 determines whether the opening degree of the ETV 14 is based on the accelerator pedal depression amount. The opening is set to be larger than the opening, which is different from the first embodiment only in this point.
[0048]
That is, as described above, although the intake air which is insufficient in the engine to which the Miller cycle is applied is supplemented by the supercharger such as the turbocharger 13, the pump loss is relatively large in the low and medium load region of the engine 1, and the operation of the engine is relatively large. Low efficiency.
Therefore, in the second embodiment, in addition to the control of the closing timing of the intake valve 5 in the first embodiment described above, the engine 1 is operated in a low-medium load region based on information from the accelerator position sensor 4. If it is determined that the intake air amount has been reduced, the ECU 40 increases the opening of the ETV 14 to compensate for the decrease in the intake air amount. By increasing the opening degree of the ETV 14, the intake resistance can be reduced to increase the intake flow rate, and the pump loss can be reduced.
[0049]
Thus, in addition to the effects of the above-described first embodiment, drivability is further improved, and fuel consumption is improved by reducing pump loss. Note that such opening control of the ETV 14 is performed by controlling the operation of the throttle actuator 14a.
Since the high expansion ratio cycle engine according to the second embodiment of the present invention is configured as described above, if it is determined that the engine 1 is in the transition to acceleration or is operating in the low to medium speed range, The VVT 30 is controlled by the ECU 40. That is, in the case of the Miller cycle of the early intake closing, the closing timing of the intake valve 5 is changed to the retard side so that the intake air amount increases. Further, when the vehicle is operated in a low-medium load range, the operation of the actuator 14a is controlled by the ECU 40 such that the opening of the ETV 14 becomes larger than the original ETV opening corresponding to the accelerator pedal depression amount.
[0050]
Hereinafter, the operation of the high expansion ratio cycle engine according to the second embodiment of the present invention will be briefly described. In addition to the flowchart (see FIG. 3) described in the first embodiment, its operation is performed according to the flowchart shown in FIG. Is controlled. That is, in step S11, information from the engine speed sensor 3, the accelerator position sensor 4, and the like is taken in. Next, in step S12, it is determined whether or not the engine 1 is operating in a low-medium load region. . Then, when it is determined that the engine 1 is operating in the low-medium load range, the process proceeds to step S13 through the Yes route, the operation of the VVT 30 is controlled, and the closing timing of the intake valve 5 is retarded. Controlled.
[0051]
Thereafter, the process proceeds to step S14, in which the opening of the ETV 14 is controlled to increase and the process returns. In this case, the opening of the ETV 14 may be set by, for example, multiplying the original required opening amount θ of the driver based on the accelerator pedal depression amount by a predetermined coefficient k (k> 1), or the predetermined opening Δθ. (Δθ> 0) may be set.
[0052]
Therefore, according to the high expansion ratio cycle engine according to the second embodiment of the present invention, in addition to the advantages of the above-described first embodiment, in a low to middle load region, the intake air flow rate is further increased and the pump loss is reduced. As a result, there is an advantage that fuel economy is improved and drivability is further improved. Further, even when the VVT 30 does not operate for some reason, by further increasing the opening degree of the ETV 14, it is possible to avoid a decrease in drivability due to a malfunction of the VVT 30.
[0053]
The present invention is not limited to the above embodiments. For example, in each of the above-described embodiments, the case where the early intake closing type mirror cycle is applied has been described. However, the present invention may be applied to a late intake closing type mirror cycle (see the acupressure diagram in FIG. 7). In this case, when it is determined that the engine is in the transition of acceleration or in the low-to-medium-speed region, the closing timing of the intake valve 5 may be advanced so that the intake air amount increases.
[0054]
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. 5 may be applied.
[0055]
Further, the engine to which the present invention is applied is not limited to the above-described in-cylinder injection type spark ignition type engine, and it is needless to say that the present invention can be applied to a port injection type engine.
In the above-described embodiment, whether or not the intake air amount has reached the target intake air amount is determined using information from an AFS (air flow sensor). However, a pressure sensor (boost pressure sensor) ) To determine whether or not the actual intake air pressure is greater than the target intake air pressure based on the boost pressure obtained by the pressure sensor, thereby determining whether or not the intake air amount is equal to or less than the target value. Good.
[0056]
【The invention's effect】
As described in detail above, according to the high expansion ratio cycle engine of the present invention, when the intake air amount is small until the boost pressure rises during the acceleration transition, the intake valve is increased so that the intake air amount increases. Since the valve closing timing is controlled, it is possible to prevent output torque shortage due to a decrease in the amount of combustion. As a result, sufficient acceleration can be obtained even during an acceleration transition, and drivability is improved. In addition, since the technology of the variable valve timing mechanism that has already been put to practical use can be applied, there is an advantage that mechanical reliability is high (claims 1, 3, and 4).
Further, according to the high expansion ratio cycle engine of the present invention, in the operating region where the supercharging pressure in the low to middle speed range is low, the closing timing of the intake valve is controlled so as to increase the intake air amount. Insufficient output torque due to a decrease in the driving force can be eliminated, and drivability is improved. Further, since the technology of the variable valve timing mechanism that has already been put to practical use can be applied, there is an advantage that mechanical reliability is high (claims 2, 3, and 4).
According to the high expansion ratio cycle engine of the present invention, when the engine is operated in a low to medium load range, the opening of the throttle valve is set to be larger than the driver's required opening based on the accelerator pedal depression amount. Thus, there is an advantage that the intake air flow rate can be further increased and the pump loss can be reduced, so that fuel efficiency can be improved and drivability can be further improved. Further, even when the variable valve timing mechanism does not operate for some reason, by increasing the opening amount of the throttle valve, there is an advantage that drivability can be reduced as much as possible due to a malfunction of the variable valve timing mechanism. (Claim 5).
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an overall configuration of a high expansion ratio cycle engine according to a first 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 the high expansion ratio cycle engine according to the first embodiment of the present invention.
FIG. 3 is a flowchart illustrating an operation of the high expansion ratio cycle engine according to the first embodiment of the present invention.
FIG. 4 is a flowchart illustrating an operation of a high expansion ratio cycle engine according to a second embodiment of the present invention.
FIG. 5 is a schematic diagram for explaining another example of the variable valve timing mechanism applied to the present invention.
FIG. 6 is an acupressure diagram illustrating an example of a conventional high expansion ratio cycle engine.
FIG. 7 is an acupressure diagram illustrating another example of a conventional high expansion ratio cycle engine.
[Explanation of symbols]
1 engine 5 intake valve 13 turbocharger (supercharger)
14 ETV (Drive-by-wire slot valve)
30 VVT (variable valve timing mechanism)
40 ECU (control means)
41 Acceleration transition judgment means 42 Operating speed area judgment means

Claims (5)

In a high expansion ratio cycle engine equipped with a supercharger while setting the expansion ratio higher than the compression ratio,
An acceleration transient determination means for determining an engine acceleration transient;
A variable valve timing mechanism capable of changing a closing timing of an intake valve of the engine;
Control means for controlling the operation of the variable valve timing mechanism,
When the transient state of the engine is determined by the transient state determining means, the control means controls the operation of the variable valve timing mechanism so as to increase the intake air amount. Cycle engine. In a high expansion ratio cycle engine equipped with a supercharger while setting the expansion ratio higher than the compression ratio,
Operating speed region determining means for determining an operating speed region of the engine;
A variable valve timing mechanism capable of changing a closing timing of an intake valve of the engine;
Control means for controlling the operation of the variable valve timing mechanism,
When the operating speed region determining means determines that the operating speed region of the engine is a low-medium speed region, the control means controls the operation of the variable valve timing mechanism so as to increase the intake air amount. Features a high expansion ratio cycle engine. An intake valve early closing type high expansion ratio cycle engine, wherein the engine is configured to close the intake valve in the middle of an intake stroke so that an expansion ratio is larger than a compression ratio. 3. The high expansion ratio cycle engine according to claim 1, wherein the intake air amount is increased by delaying a valve closing timing of the engine. An intake valve late closing type high expansion ratio cycle engine, wherein the engine is configured to close the intake valve in the middle of a compression stroke so that an expansion ratio becomes larger than a compression ratio. 3. The high expansion ratio cycle engine according to claim 1, wherein the intake air amount is increased by advancing the valve closing timing of the engine. The engine includes a drive-by-wire type slot valve whose opening is controlled based on a control signal from the control means,
The engine according to any one of claims 1 to 4, wherein when the engine is operated in a low to medium load range, the opening of the throttle valve is set to be larger than a driver's required opening based on the accelerator pedal depression amount. 2. The high expansion ratio cycle engine according to claim 1.

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