JP2004183513A - High compression ratio cycle engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a lowering of output by increasing the intake air quantity during the accelerating transition and operation in a low-medium speed range of a high expansion ratio cycle engine. <P>SOLUTION: In the high expansion ratio cycle engine with a supercharger, when the engine 1 is determined to be in the accelerating transition, a drive-by-wire mechanism 14 is preferentially operated to increase the intake air quantity, and in case the insufficient portion of the intake air quantity cannot be compensated by the drive-by-wire mechanism 14, the valve closing timing of an intake valve 5 is changed by a variable valve timing mechanism 30 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 it is attempted to greatly increase the expansion ratio (= compression ratio) 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 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.
[0005]
Hereinafter, an engine to which such a Miller cycle is applied will be briefly described with reference to the acupressure diagrams of FIGS. 5 and 6. Among them, FIG. 5 shows a finger pressure diagram of a so-called intake valve early closing type Miller cycle engine in which the intake valve closes earlier than the piston reaches the bottom dead center, and FIG. 6 shows 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.
[0006]
First, the operation of the Miller cycle engine of the intake valve early closing type will be described with reference to FIG. 5. When the piston descends from top dead center (TDC: point a in the figure) and the intake stroke starts, the in-cylinder pressure increases. 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.
[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 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.
[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 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.
[0009]
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.
[0010]
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.
[0011]
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. 6 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.
[0012]
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.
[0013]
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.
[0014]
[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.
[0016]
The present invention has been made in view of such a problem, and provides a high expansion ratio cycle engine in which the intake air amount is increased at the time of acceleration transition or in a low to middle speed range to prevent a decrease in output. With the goal.
[0017]
[Means for Solving the Problems]
For this reason, in the high compression ratio cycle engine according to the first aspect of 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 acceleration transition, first, the operation of the drive-by-wire mechanism is controlled so that the intake air amount increases. If the intake air amount is still insufficient even after the operation control of the drive-by-wire mechanism, the operation of the variable valve timing mechanism is controlled so that the intake air amount also increases. In other words, to compensate for the shortage of intake air during transient acceleration, the drive-by-wire mechanism is preferentially activated to increase the amount of intake air by increasing the throttle opening, and the intake air is still insufficient If so, the variable valve timing mechanism is operated to compensate for the shortage of the intake air amount. Therefore, sufficient acceleration can be obtained even during acceleration transition, and drivability is improved. Also, since the drive-by-wire mechanism is operated with priority over the variable valve timing mechanism to increase the amount of intake air, a high expansion ratio can be maintained as much as possible, and a decrease in thermal efficiency can be prevented.
[0018]
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 drive-by-wire mechanism is controlled first so that the intake air amount increases. Then, even after the operation control of the drive-by-wire mechanism, if the intake air amount is still insufficient, the operation of the variable valve timing mechanism is controlled so that the intake air amount increases. In other words, when the engine operating range is low to medium speed, when the shortage of the intake air is compensated, the drive-by-wire mechanism is preferentially operated to increase the throttle opening to increase the intake air. If the intake air amount is still insufficient, the variable valve timing mechanism is operated to compensate for the insufficient intake air amount. Therefore, sufficient acceleration can be obtained even during operation in a low to medium speed range, and drivability is improved. Also, since the drive-by-wire mechanism is operated with priority over the variable valve timing mechanism to increase the amount of intake air, a high expansion ratio can be maintained as much as possible, and a decrease in thermal efficiency can be prevented.
[0019]
Preferably, the operation of the variable valve timing mechanism is controlled so that the intake air amount increases when the intake air amount is insufficient even when the throttle opening is maximized by the drive-by-wire mechanism.
Preferably, the engine is a high-expansion-ratio cycle engine of an intake valve early closing type configured to close the intake valve in the middle of the intake stroke so that the expansion ratio becomes larger than the compression ratio. Thus, the intake air amount is increased by delaying the closing timing of the intake valve.
[0020]
Preferably, the engine is a high-expansion-ratio cycle engine of an intake valve late closing type configured to close the intake valve in the middle of a compression stroke so that the expansion ratio is larger than the compression ratio. Thus, the intake air amount is increased by advancing the closing timing of the intake valve.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a high expansion ratio cycle engine according to one 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 the present embodiment, the Miller cycle of the intake valve early closing type described in the section of the related art is applied.
[0022]
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.
[0023]
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.
[0024]
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 in the figure, the intake manifold 10 has a drive-by-wire type throttle valve (ETV) 14 for adjusting the amount of intake air, and a throttle position sensor (TPS) for detecting the opening of the throttle valve 14 (throttle opening). ) 16 and an intake air amount sensor (air flow sensor or AFS) 18 as an actual intake air amount detecting means for measuring an intake air amount.
[0025]
Here, the ETV (drive-by-wire mechanism) 14 is electrically connected to an accelerator pedal (not shown), and basically, the throttle opening is changed according to the accelerator pedal depression amount of the driver. . Further, as shown in the figure, the ETV 14 has 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 described later.
[0026]
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.
[0027]
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 above-mentioned TPS 16 and AFS 18 are connected to the input side of the ECU 40, an engine speed sensor 3 for detecting the engine speed Ne, and an accelerator position sensor for detecting the accelerator pedal depression amount (ie, engine load) Acc of the driver. 4 is also connected. Furthermore, also connected a pressure sensor for detecting the pressure of the O ₂ sensor and the intake passage 10 (not shown).
[0028]
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, and 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.
[0029]
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 specifically described. The variable valve timing mechanism variable (VVT) 30 capable of changing the operation timing of the intake valve 5 is provided in the valve mechanism on the intake valve side of the engine 1. Have been. 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.
[0030]
Further, inside the ECU 40, an acceleration transition time determining means 41 for determining whether or not the engine 1 is in an acceleration transient state based on an operating state of the engine 1, and an operating speed area determining means for determining an operating speed area of the engine 1 are provided. 42 are provided.
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.
[0031]
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.
[0032]
In addition to the above, the ECU 40 is provided with a target intake air amount setting means 43, a comparing means 44, and a throttle opening degree setting means 46. 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).
[0033]
The comparing means 44 compares the target value (target intake amount) Vt of the intake air amount set by the target intake air amount setting means 43 with the actual intake air amount (actual intake air amount) Vr detected by the AFS 18. Specifically, the difference ΔV (= Vr−Vt) between the actual intake air amount Vr and the target intake air amount Vt is calculated.
The throttle opening setting means 46 is for setting the opening of the ETV 14, and the operation of the actuator 14a of the ETV 14 is feedback-controlled so that the throttle opening set by the throttle opening setting means 46 is obtained. It has become.
[0034]
In particular, in the present embodiment, when the operating state of the engine 1 is determined to be in the transient acceleration state by the acceleration transient determination means 41, or when the engine is operated in the low and medium speed range by the operating speed area determination means 42. If it is determined that the intake air amount is insufficient, the throttle opening degree is set to be larger by the throttle opening degree setting means 46 than in the normal operation in order to compensate for the shortage of intake air in the engine 1.
[0035]
Specifically, when it is determined that the engine 1 is in the transitional state of acceleration or in the low / medium speed range, the comparison unit 44 determines the intake air amount Vt set by the target intake air amount setting unit 43 and the AFS 18. By comparing the detected actual intake air amount Vr with the detected actual intake air amount Vr, if it is determined that the actual intake air amount Vr is equal to or less than the target intake air amount Vt (that is, if ΔV ≦ 0), it is determined that the intake air amount is insufficient. Thus, a control signal is output from the throttle opening setting means 46 to the throttle actuator 14a such that the opening is increased by a predetermined opening Δθ with respect to the current throttle opening.
[0036]
This is mainly due to the following reasons. 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.
[0037]
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. .
[0038]
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.
[0039]
Therefore, as described above, when it is determined that the operating state of the engine 1 is in the transition to acceleration or the engine 1 is operating in the low-to-medium speed range, first, the target intake air amount Vt and the actual intake air amount Vr are determined. To determine whether or not the actual intake air amount Vr has reached the target intake air amount Vt. If the actual intake air amount Vr is equal to or less than the target intake air amount Vt, a predetermined opening amount with respect to the current throttle opening degree is determined. By increasing the throttle opening, the amount of intake air is increased to suppress a decrease in output during transient acceleration or the like.
[0040]
Then, after such throttle opening control, the calculation result of the comparing means 44 is referred to again, and if the actual intake air amount Vr has reached the target intake air amount Vt, the above-mentioned Δθ is set to the throttle opening degree set during normal operation. The sum is set as the final throttle opening. If the actual intake air amount Vr has not reached the target intake air amount Vt, the throttle opening is further increased by the predetermined opening Δθ, and the predetermined opening Δθ is repeatedly increased until the actual intake air amount Vr matches the target intake air amount Vt. The throttle opening is increased.
[0041]
If the actual intake air amount Vr has not reached the target intake air amount Vt even though the opening degree of the ETV 14 by the throttle actuator 14a has reached the maximum value, the VVT 30 is operated to retard the closing timing of the intake valve 5. As a result, 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.
[0042]
As described above, in the high expansion ratio engine according to the present embodiment, when the operating state is such that the amount of intake air is insufficient (that is, during the acceleration transition of the engine 1 or during the operation in the low-to-medium speed range), first, the throttle actuator is operated. 14a, the opening of the ETV 14 is increased to increase the intake air amount. If the intake air amount is still insufficient even when the opening of the ETV 14 is maximized, the VVT 30 is operated to increase the intake air amount. . When the shortage of the intake air amount can be resolved by controlling the opening of the ETV 14, the operation control of the VVT 30 is not executed.
[0043]
Next, the reason why the opening degree control of the ETV 14 is preferentially performed and the operation control of the VVT 30 is subsequently performed when increasing the intake air amount will be described.
As described above, in the Miller cycle (high expansion ratio cycle) engine to which the present invention is applied, the pump loss is reduced by making the expansion ratio ε relatively larger than the geometric compression ratio ρ. Improving thermal efficiency. Specifically, the closing timing of the intake valve 5 is set as far as possible from the bottom dead center to reduce the substantial intake stroke, thereby reducing the geometric compression ratio ρ to be smaller than the expansion ratio ε.
[0044]
Therefore, when the VVT 30 is operated to delay the valve closing timing of the intake valve 5 to the vicinity of the bottom dead center when the intake air amount is insufficient, the intake air amount can be increased, but a cycle close to the Otto cycle is performed during this time. Thus, the original advantage of the Miller cycle is lost. That is, in this case, the pump loss increases relative to the Miller cycle, and the thermal efficiency also decreases.
[0045]
On the other hand, when the operation control of the ETV 14 is performed, the operation of the throttle actuator 14a is controlled in a direction to increase the throttle opening, so that the pumping loss acts in a direction to decrease. Therefore, in this case, the pumping loss can be reduced, and the thermal efficiency does not decrease.
[0046]
Therefore, in the high expansion ratio engine according to the present embodiment, in an operating state in which the intake air amount is insufficient, such as during acceleration of the engine 1 or during operation in a low-to-medium speed range, first, the opening degree of the ETV 14 is positively increased. Is controlled to increase the intake air amount. If the intake air amount is still insufficient, the VVT 30 is operated to increase the intake air amount.
[0047]
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.
[0048]
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.
[0049]
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.
[0050]
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.
[0051]
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).
[0052]
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 one embodiment of the present invention is configured as described above, based on the information from the engine speed sensor 3 and the accelerator position sensor 4, the ECU 40 determines whether or not the engine 1 is in a transient state. In a state in which the sub rocker arm 33a is not operating at a high speed, the mode is switched to a mode in which the sub rocker arm 33a operates in cooperation with the main rocker arm 33c.
[0053]
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 the point b in FIG. 5), the intake valve 5 is closed, whereby the substantial intake stroke ends.
[0054]
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).
[0055]
On the other hand, if the ECU 40 determines that the engine 1 is in the transition of acceleration or is operating in the low to medium speed range based on the information from the engine speed sensor 3 and the accelerator position sensor 4, the target intake air amount setting is performed. The comparing unit 44 compares the target value (target intake amount) Vt of the intake amount set by the unit 43 with the actual intake amount (actual intake amount) Vr detected by the AFS 18. As a result, when it is determined that the actual intake air amount Vr is equal to or less than the target intake air amount Vt, the opening control of the ETV 14 is executed by the throttle opening setting means 46.
[0056]
That is, in this case, a control signal is output from the throttle opening setting means 46 to the throttle actuator 14a so that the opening of the ETV 14 increases by the predetermined opening Δθ in order to increase the intake air amount. Then, the actual intake air amount Vr and the target intake air amount Vt are compared again by the comparing means 4, and if the actual intake air amount Vr is still equal to or smaller than the target intake air amount Vt, the opening of the one-stage throttle actuator 14a is further increased. Thus, the actual intake air amount Vr is increased. Then, such control is repeated, and the opening control of the ETV 14 is executed such that the actual intake air amount Vr and the target intake air amount Vt match.
[0057]
If the actual intake air amount Vr is less than the target intake air amount Vt even when the opening degree of the ETV 14 reaches the maximum value, the VVT 30 is operated. Specifically, the link operation between the sub rocker arm 33a and the main rocker arm 33c is released, and the other sub rocker arm 33b is switched to a mode in which the link operation is performed with the main rocker arm 33c.
[0058]
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. That is, 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. 5). 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.
[0059]
As a result, insufficient intake air can be secured during operation in a low-medium speed range or during transient acceleration, and a decrease in output torque can be prevented.
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 and the accelerator opening Acc are taken in from the engine speed sensor 3 and the accelerator position sensor 4, respectively.
[0060]
Next, in step S2, based on the engine speed Ne and the accelerator opening Acc, it is determined whether or not the operating range of the engine 1 is in a low to medium speed range or whether or not the engine 1 is in a transient state of acceleration. Then, when the engine 1 is operating in the low-medium speed range or when the vehicle is in the transition of acceleration, the process proceeds to step S3, and otherwise returns.
[0061]
Here, when the process proceeds to step S3, that is, when the engine 1 is operating in the low-medium speed range or during transient acceleration, it is considered that the intake air amount has decreased. By comparing the actual intake air amount Vr with the target intake air amount Vt set by the target intake air amount setting means 43, it is determined whether the actual intake air amount Vr is equal to or less than the target intake air amount Vt.
[0062]
If it is determined in step S3 that the actual intake air amount Vr is equal to or less than the target intake air amount Vt, the process proceeds to step S4, where the throttle actuator 14a is controlled so that the throttle opening increases by a predetermined opening, and the intake air is increased. The amount is increased. Thereafter, the process proceeds to step S5, where the actual intake air amount Vr and the target intake air amount Vt are compared again, and if the actual intake air amount Vr has reached the target intake air amount Vt, the process returns. If not, the process proceeds to step S6. Then, in step S6, it is determined whether or not the throttle opening is at the maximum. If the throttle opening is not at the maximum, the process returns to step S4, and the processes of step S4 and step S5 are repeated again.
[0063]
Further, if it is determined in step S6 that the throttle opening is the maximum, the state becomes a limit state where it is impossible to further increase the intake air amount by the ETV 14. Therefore, in this case, the process proceeds to step S7, and the closing timing of the intake valve 5 is changed to the bottom dead center side by the VVT 30 in order to increase the intake air amount.
Therefore, according to the high expansion ratio cycle engine according to one embodiment of the present invention, when the intake air amount is small until the boost pressure rises during transient acceleration, the ETV 14 and the ETV 14 are configured to increase the intake air amount. Since the operation of the VVT 30 is controlled, the compression ratio is increased, 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 region, the operation of the ETV 14 and the VVT 30 is controlled so that the intake air amount increases as described above, so that the combustion amount decreases. There is an advantage that output torque shortage can be eliminated and drivability is improved. Further, since the technology of the drive-by-wire mechanism and the variable valve timing mechanism that have already been put to practical use can be applied, there is an advantage that the mechanical reliability is high.
[0064]
Further, as described above, when increasing the intake air amount, the opening control of the ETV 14 is executed with priority over the operation control of the VVT 30, and thereafter the operation control of the VVT 30 is executed, so that the high expansion ratio can be maintained as much as possible. A decrease in thermal efficiency can be suppressed as much as possible. Therefore, there is an advantage that both improvement in fuel efficiency and improvement in drivability can be achieved. Further, when the opening control of the ETV 14 is executed, the throttle actuator 14a is operated in a direction to increase the throttle opening, so that there is an advantage that a pumping loss can be reduced.
[0065]
The present invention is not limited to the above embodiment. For example, in the above-described embodiment, the case where the early intake-type mirror cycle is applied has been described. However, the present invention may be applied to a late intake-type mirror cycle (see the acupressure diagram in FIG. 6). 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.
[0066]
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 that can freely set the opening / closing timing and the lift amount by the driving force of the electromagnetic coils 5a and 5b as shown in FIG. 4 may be applied.
[0067]
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.
[0068]
【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 drive-by-wire mechanism is configured to increase the intake air amount. Since the throttle opening and the closing timing of the intake valve are controlled, it is possible to prevent the output torque from becoming insufficient 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 drive-by-wire mechanism and the variable valve timing mechanism that have already been put to practical use can be applied, there is an advantage that the mechanical reliability is high. In addition, since the drive-by-wire mechanism is preferentially activated over the variable valve timing mechanism to increase the amount of intake air, it is possible to reduce pumping loss and maintain a high expansion ratio as much as possible, resulting in lower thermal efficiency. Can be prevented. Therefore, there is an advantage that both improvement in fuel efficiency and improvement in drivability can be achieved (claims 1, 3 to 5).
[0069]
Further, according to the high expansion ratio cycle engine of the present invention, the throttle opening degree of the drive-by-wire mechanism and the closing timing of the intake valve are increased so that the intake air amount increases in the operating region where the supercharging pressure in the low to middle speed range is low. Is controlled, the output torque shortage due to the decrease in the combustion amount can be resolved, and the drivability is improved. In addition, since the technology of the drive-by-wire mechanism and the variable valve timing mechanism that have already been put to practical use can be applied, there is an advantage that the mechanical reliability is high. In addition, since the drive-by-wire mechanism is preferentially activated over the variable valve timing mechanism to increase the amount of intake air, it is possible to reduce pumping loss and maintain a high expansion ratio as much as possible, resulting in lower thermal efficiency. Can be prevented. Therefore, there is an advantage that both improvement in fuel efficiency and improvement in drivability can be achieved (claims 2 to 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 illustrating 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 schematic diagram for explaining another example of the variable valve timing mechanism applied to the present invention.
FIG. 5 is an acupressure diagram illustrating an example of a conventional high expansion ratio cycle engine.
FIG. 6 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 mechanism)
14a Throttle actuator 18 Air flow sensor or AFS (actual intake air amount detection means)
30 VVT (variable valve timing mechanism)
40 ECU (control means)
41 Acceleration transient judgment means 42 Operating speed area judgment means 43 Target intake air amount setting means 44 Comparison 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;
A drive-by-wire mechanism electrically connected to the accelerator pedal and capable of changing the throttle opening,
A control means for controlling operation of the variable valve timing mechanism and the drive-by-wire mechanism;
When the transient state of the engine is determined by the transient state determining means, the operation of the drive-by-wire mechanism is controlled so as to increase the intake air amount, and the intake state is maintained even after the drive-by-wire mechanism is activated. A high expansion ratio cycle engine, wherein, when it is determined that the air amount is insufficient, the operation of the variable valve timing mechanism is controlled so as to increase the intake air amount. 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;
A drive-by-wire mechanism electrically connected to the accelerator pedal and capable of changing the throttle opening,
A control means for controlling operation of the variable valve timing mechanism and the drive-by-wire mechanism;
When the operating speed range determining means determines that the operating speed range of the engine is a low to medium speed range, the operation of the drive-by-wire mechanism is controlled so that the intake air amount increases, and the drive-by-wire mechanism is controlled. The operation of the variable valve timing mechanism is controlled so that the intake air amount is increased even after the operation of the high expansion ratio cycle. engine. When the intake air amount is insufficient even when the throttle opening is maximized by the drive-by-wire mechanism, the operation of the variable valve timing mechanism is controlled so as to increase the intake air amount. The high expansion ratio cycle engine according to claim 1 or 2. 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 becomes larger than a compression ratio. The high expansion ratio cycle according to any one of claims 1 to 3, wherein a timing mechanism is configured to increase the intake air amount by delaying a closing timing of the intake valve. 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. The high expansion ratio cycle according to any one of claims 1 to 3, wherein the intake mechanism is configured to increase an intake air amount by advancing a closing timing of the intake valve by a timing mechanism. engine.

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