JP4089408B2 - High compression ratio cycle engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a high expansion ratio cycle engine in which an expansion ratio is set larger than a compression ratio.
[0002]
[Prior art]
2. Description of the Related Art Otto-cycle gasoline engines having four strokes (intake, compression, expansion, and exhaust) have been widely used as driving sources for vehicles such as automobiles. In such a gasoline engine, the thermal efficiency is improved by various improvements and devices, but there is a demand for further improving the thermal efficiency.
[0003]
In order to improve thermal efficiency, it is known that the expansion ratio can be increased by extending the stroke when the engine is expanded. However, in the Otto cycle, the piston stroke is the same in each stroke, and the expansion ratio and compression are the same. The ratio is equal. For this reason, when the expansion ratio is increased, the compression ratio is also increased, and the air-fuel mixture is ignited early in the combustion chamber due to the heat generated by the compression, and knocking is likely to occur. Therefore, even if the expansion ratio (= compression ratio) is greatly increased in order to improve the thermal efficiency, the limit is low, and it is difficult to substantially increase the expansion ratio.
[0004]
Therefore, conventionally, the intake amount is limited by greatly advancing the closing timing of the intake valve or delaying the closing timing of the intake valve substantially, and the expansion ratio is substantially reduced by the compression ratio. An engine with a high expansion ratio cycle (hereinafter also referred to as Miller cycle or Atkinson cycle), which is set to be larger than that, has been put into practical use. Moreover, as a technique regarding such a mirror cycle engine, for example, Patent Document 1 and Patent Document 2 disclose the technique.
[0005]
Hereinafter, an engine to which such a mirror cycle is applied will be briefly described with reference to the acupressure diagrams of FIGS. Among these, FIG. 5 is a finger pressure diagram of a so-called intake valve early closing type mirror cycle engine that closes the intake valve at an earlier timing than the piston reaches bottom dead center, and FIG. 6 shows that the piston has reached bottom dead center. It is a shiatsu diagram of a so-called intake valve slow closing type Miller cycle engine which closes an intake valve at a later timing.
[0006]
First, the operation of the intake cycle early closing type mirror cycle engine will be described with reference to FIG. 5. When the piston descends from the top dead center (TDC: point a in the figure) and the intake stroke starts, the in-cylinder pressure becomes Intake (or mixture) is taken in from the intake valve while maintaining substantially atmospheric pressure. Then, the intake valve is closed at a predetermined timing (point b in the figure) before the bottom dead center (BDC), thereby completing the substantial intake stroke.
[0007]
Thereafter, the in-cylinder pressure decreases as the piston descends, and the intake stroke ends when the piston reaches bottom dead center (point c in the figure). Then, when the piston reverses upward, the intake stroke shifts to the compression stroke, and the in-cylinder pressure gradually increases as the piston rises. When the piston further rises and the in-cylinder pressure becomes higher than the pressure at the point b (point d in the figure), the substantial compression between the piston stroke position and the top dead center (point e in the figure) at this time The intake air is compressed in the stroke.
[0008]
When the piston reaches the top dead center, the compression stroke ends and the expansion stroke starts. That is, the air-fuel mixture is ignited and combusted in the vicinity of the top dead center of the piston, and the in-cylinder pressure suddenly rises due to the combustion pressure and the piston turns downward (point f in the figure). Then, when the piston reaches the bottom dead center (g point in the figure), it shifts from the expansion stroke to the exhaust stroke, and the combustion gas is discharged at a substantially atmospheric pressure. Further, when the piston reaches top dead center (point a in the figure), a series of mirror cycles is completed, and the intake stroke is started again.
[0009]
In such a mirror cycle of the intake valve early closing type, the intake amount is reduced by closing the intake valve at a timing (point b in the figure) much earlier than the piston reaches the bottom dead center. The compression ratio is greatly reduced.
In addition, since the expansion stroke is from the top dead center to the bottom dead center of the piston as in the past, the expansion stroke is relatively larger than the substantial compression stroke, and thus the expansion ratio ε> the actual compression ratio ρ. be able to. Hereinafter, the actual compression ratio is also referred to as a geometric compression ratio.
[0010]
Thus, by making the expansion ratio ε larger than the geometric compression ratio ρ, it is possible to reduce pump loss (pumping loss) and improve thermal efficiency. Further, knocking (knocking) can be avoided by reducing the compression ratio (for example, compression ratio ρ = 9, ε = 14). However, in such a mirror cycle, the intake amount decreases with respect to the exhaust amount, so the output becomes relatively low. Therefore, conventionally, the intake air is supercharged by a supercharger to ensure output.
[0011]
Such a mirror cycle engine can be realized only by changing the shape of the intake cam as compared with a general Otto cycle engine.
Also, the intake valve late closing type mirror cycle shown in FIG. 6 operates in the same manner as the intake valve early closing type described above except that the intake valve closing timing is different. That is, when the piston descends from top dead center (point a in the figure) and the intake stroke is started, intake (or mixture) is taken in from the intake valve while the in-cylinder pressure is maintained at substantially atmospheric pressure.
[0012]
Even after the piston reaches the bottom dead center (point c in the figure), the state in which the intake valve is opened is maintained, whereby the compression stroke is started while the in-cylinder pressure remains at atmospheric pressure. The intake valve is closed at a predetermined timing after the bottom dead center (point b ′ in the figure), and a substantial compression stroke is started from this point. The subsequent steps are the same as those of the intake valve early closing type.
[0013]
Therefore, like the above-described intake valve early closing type Miller cycle engine, the intake stroke late closing type Miller cycle engine also has a relatively larger expansion stroke than the substantial compression stroke, thereby causing the expansion. Ratio ε> geometric compression ratio ρ.
[0014]
[Patent Document 1]
Japanese Patent Publication No. 7-91984
[Patent Document 2]
Japanese Patent No. 3236654
[0015]
[Problems to be solved by the invention]
As described above, in the Miller cycle engine, the intake air is supercharged by the supercharger because the intake air amount decreases with respect to the exhaust gas amount. However, such conventional technology has the following problems. It was.
That is, the turbocharger generally has a time lag between the time the accelerator is depressed and the turbocharging is performed. For this reason, during the acceleration transition, the intake air amount decreases until the boost pressure rises. As a result, the torque becomes insufficient and an acceleration failure occurs. In the Miller cycle, the lower the compression ratio and the higher the expansion ratio, the higher the heat efficiency. There is a risk of lowering.
[0016]
The present invention was devised in view of such a problem, and provides a high expansion ratio cycle engine that prevents an output decrease by increasing the intake air amount during acceleration transients and at low and medium speed ranges. With the goal.
[0017]
[Means for Solving the Problems]
For this reason, the high compression ratio cycle engine according to the first aspect of the present invention is a high expansion ratio cycle engine in which the expansion ratio is set larger than the compression ratio and the turbocharger is provided. When it is determined that the state is an acceleration transient, the operation of the drive-by-wire mechanism is first controlled so that the intake air amount increases. If the intake air amount is still insufficient after the drive-by-wire mechanism is controlled, then the operation of the variable valve timing mechanism is controlled so that the intake air amount increases. In other words, to compensate for the shortage of intake air during acceleration transients, the drive-by-wire mechanism is preferentially operated to increase the throttle opening, and the intake air amount is still insufficient. If this is the case, the variable valve timing mechanism is operated to compensate for the shortage of intake air. Therefore, sufficient acceleration can be obtained even during acceleration transition, and drivability is improved. In addition, since the drive-by-wire mechanism is preferentially operated over the variable valve timing mechanism to increase the intake air amount, 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, the high expansion ratio cycle engine of the present invention is a high expansion ratio cycle engine in which the expansion ratio is set larger than the compression ratio and the supercharger is provided. When it is determined that the speed region is the low / medium speed region, the operation of the drive-by-wire mechanism is first controlled so that the intake air amount increases. If the intake air amount is still insufficient after the drive-by-wire mechanism is controlled, then the operation of the variable valve timing mechanism is controlled so that the intake air amount increases. In other words, when the shortage of intake air amount is compensated because the engine operating range is low and medium speed range, the drive-by-wire mechanism is preferentially operated to increase the throttle opening, thereby increasing the intake air amount. 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 the low and medium speed ranges, and drivability is improved. In addition, since the drive-by-wire mechanism is preferentially operated over the variable valve timing mechanism to increase the intake air amount, 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 such that an expansion ratio is larger than a compression ratio by closing the intake valve in the middle of an intake stroke. Thus, the intake amount is increased by retarding the closing timing of the intake valve.
[0020]
Preferably, the engine is a high expansion ratio cycle engine of an intake valve slow closing type configured to make the expansion ratio larger than the compression ratio by closing the intake valve in the middle of the compression stroke. Thus, the intake amount is increased by advancing the closing timing of the intake valve.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a high expansion ratio cycle engine according to an embodiment of the present invention will be described with reference to the drawings. The engine 1 shown in FIG. 1 has a high expansion ratio cycle (Miller cycle or Atkinson cycle) in which the expansion ratio is set larger than the compression ratio. In this embodiment, the intake valve early closing type mirror cycle described in the section of the prior art is applied.
[0022]
The engine 1 is a so-called in-cylinder injection type spark ignition engine that supplies fuel directly into a cylinder, and includes fuel injection in an intake stroke (intake stroke injection) and fuel injection in a compression stroke (compression stroke). (Injection) can be switched.
This in-cylinder injection engine 1 is operated at a stoichiometric air fuel ratio (stoichio), an operation at a rich air fuel ratio (rich A / F) (rich air fuel ratio operation), or a lean air fuel ratio (lean A / F). Operation (lean air-fuel ratio operation) is possible, and the above-mentioned plurality of operation modes are switched according to conditions obtained from various parameters.
[0023]
The cylinder head 2 of the engine 1 is provided with a spark plug (not shown) and a fuel injection valve 6 for each cylinder, and a fuel supply device (not shown) is connected to each fuel injection valve 6. ing. This fuel supply apparatus has a low-pressure fuel pump and a high-pressure fuel pump. After the fuel in the fuel tank is pressurized to a low pressure or a high pressure, the fuel is supplied to the fuel injection valve 6.
[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 the upper end of each intake port 9. As shown in the figure, the intake manifold 10 includes a drive-by-wire throttle valve (ETV) 14 that adjusts the amount of intake air, and a throttle position sensor (TPS) that detects the opening (throttle opening) of the throttle valve 14. ) 16 and an intake air amount sensor (air flow sensor or AFS) 18 as an actual intake air amount detecting means for measuring the intake air amount.
[0025]
Here, the ETV (drive-by-wire mechanism) 14 is electrically connected to an accelerator pedal (not shown), and the throttle opening is basically changed in accordance with the depression amount of the accelerator pedal of the driver. . 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]
The cylinder head 2 has an exhaust port 11 for each cylinder, and an exhaust manifold 12 is connected to each exhaust port 11. The exhaust manifold 12 is provided with a turbocharger (supercharger) 13 that pressurizes intake air by exhaust energy. As described in the section of the prior art, this is because the intake amount of the Miller cycle engine decreases with respect to the exhaust amount. The turbocharger 13 secures the intake amount, that is, the output. Although omitted in FIG. 1, a compressor of a turbocharger 13 is interposed on the intake passage 10.
[0027]
On the other hand, the ECU 40 includes an input / output device, a storage device (ROM, RAM, nonvolatile RAM, etc.), a calculation device (CPU), a timer counter, and the like. Is to be executed. The TPS 16 and AFS 18 are connected to the input side of the ECU 40, and the engine speed sensor 3 for detecting the engine speed Ne and the accelerator position sensor for detecting the accelerator pedal depression amount (that is, engine load) Acc of the driver. 4 is also connected. Further, O (not shown) ₂ A sensor and a pressure sensor for detecting the pressure in the intake passage 10 are also connected.
[0028]
Various output devices such as the fuel injection valve 6 and the actuator 14a of the ETV (throttle valve) 14 are connected to the output side of the ECU 40, and control signals from the ECU 40 are connected to these output devices. It is designed to be entered. Specifically, in the ECU 40, a target air-fuel ratio (A / F), a target ignition timing, and the like are set based on information from various sensors, and the fuel injection valve 6 is set so as to be the target air-fuel ratio and the target ignition timing. The drive pulse width and the drive amount of the throttle actuator 14a are set.
[0029]
As a result, an appropriate amount of fuel is injected from the fuel injection valve 6 at an appropriate timing, spark ignition is performed at an appropriate timing by the spark plug, and the ETV 14 is driven to open and close at an appropriate opening at an appropriate timing. It has become so.
Next, the main part of the present invention will be described in detail. The valve mechanism on the intake valve side of the engine 1 is provided with a variable valve timing mechanism variable (VVT) 30 capable of changing the operation timing of the intake valve 5. It has been. The VVT 30 is configured so that at least the closing timing of the intake valve 5 can be changed. As will be described in detail later, for example, a known VVT 30 as shown in FIGS. 2A and 2B is applied. Yes.
[0030]
Further, in the ECU 40, acceleration transient determination means 41 for determining whether or not the engine 1 is in acceleration transient based on the operation state of the engine 1 and an operation speed area determination means for determining the operation speed area of the engine 1 42 is provided.
Here, the acceleration transient determining means 41 determines whether or not it is during acceleration transient based on the accelerator pedal depression amount Acc detected by the accelerator position sensor 4 and its change amount ΔAcc. When the amount Acc is equal to or greater than the predetermined value a and the accelerator pedal depression amount ΔAcc is equal to or greater than the predetermined value b (≧ 0), the acceleration transient determination means 41 determines that the acceleration is transient. Note that the method for determining whether or not the vehicle is in an acceleration transition is not limited to the above-described method. For example, the engine load such as the intake air amount A / N of the engine 1 or the pressure in the intake passage 10 based on detection information from the AFS 18 is used. You may make it determine based on.
[0031]
Further, the operating speed region determining means 42 determines the operating speed region of the engine 1 based on the engine speed Ne detected by the engine speed sensor 3 and the engine speed is a predetermined speed Ne1. If it is less than this, it is determined that the vehicle is in the low / medium speed region, and if it is greater than or equal to the predetermined rotation speed Ne1, it is determined that it is in the high speed region.
[0032]
In addition to the above, the ECU 40 is provided with target intake air amount setting means 43, comparison means 44, and throttle opening setting means 46. Among these, the target intake air amount setting means 43 sets a target value Vt of the intake air amount of the engine 1 (hereinafter simply referred to as the intake amount) based on the engine speed Ne, the accelerator pedal depression amount (load) Acc, and the like. For example, the target value Vt is read from a map (not shown).
[0033]
The comparison unit 44 compares the target value (target intake air amount) Vt of the intake air amount set by the target intake air amount setting unit 43 with the actual intake air amount (actual intake air amount) Vr detected by the AFS 18. More specifically, a difference ΔV (= Vr−Vt) between the actual intake air amount Vr and the target intake air amount Vt is calculated.
The throttle opening setting means 46 sets 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 come to be.
[0034]
In particular, in the present embodiment, it is determined that the operating state of the engine 1 is the acceleration transient state by the acceleration transient determining unit 41 or the engine is operated in the low / medium speed region by the operating speed region determining unit 42. If it is determined, the throttle opening is set larger than that during normal operation by the throttle opening setting means 46 in order to compensate for the intake amount deficient in the engine 1.
[0035]
Specifically, when it is determined that the engine 1 is in an acceleration transition state or in an operating state in the low / medium speed region, the comparison unit 44 uses the intake air amount Vt set by the target intake air amount setting unit 43 and the AFS 18. When the actual intake air amount Vr is compared with the detected actual intake air amount Vr and it is determined that the actual intake air amount Vr is equal to or smaller than the target intake air amount Vt (that is, when 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 so that the opening increases 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 intake cycle early closing type mirror cycle engine in the present embodiment, the intake amount is reduced by closing the intake valve 5 at a timing much earlier than the piston reaches the bottom dead center during the intake stroke. Thus, the mirror cycle is realized by the expansion ratio ε> the actual compression ratio (geometric compression ratio) ρ.
[0037]
And by making the expansion ratio ε larger than the geometric compression ratio ρ in this way, the pump loss is reduced to improve the thermal efficiency, and knocking (for example, the compression ratio ρ = 9) is knocked ( Knock) is avoided. However, in such a mirror cycle, since the intake air amount decreases with respect to the exhaust gas amount, the output becomes relatively low. Therefore, as described above, the turbocharger 13 supercharges the intake air to ensure the output. .
[0038]
However, the turbocharger 13 generally has a time lag between when the accelerator is depressed and when supercharging is performed. The same applies to a so-called supercharger that extracts driving force from the crankshaft and compresses intake air. For this reason, during the acceleration transition, the intake air amount is insufficient until the boost pressure rises, resulting in acceleration failure. In the Miller cycle, the lower the compression ratio and the higher the expansion ratio, the higher the thermal efficiency. However, if the compression ratio is too low, the intake air amount is low and the output is low when the supercharging pressure in the low and medium speed ranges is low. There is a risk of lowering.
[0039]
Therefore, as described above, when it is determined that the operating state of the engine 1 is in an acceleration transient state or the engine 1 is operating in the low / medium speed range, first, the target intake air amount Vt and the actual intake air amount Vr are determined. Are compared 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 less than or equal to the target intake air amount Vt, only a predetermined opening amount with respect to the current throttle opening amount is determined. By increasing the throttle opening, the intake air amount is increased to suppress a decrease in output during acceleration transients or the like.
[0040]
Then, after such throttle opening control, the calculation result of the comparison means 44 is referred again, and if the actual intake air amount Vr reaches the target intake air amount Vt, the above Δθ is set to the throttle opening set during normal operation. The sum is set as the final throttle opening. Further, if the actual intake air amount Vr does not reach the target intake air amount Vt, the throttle opening is further increased by a predetermined opening Δθ, and the predetermined opening Δθ is repeatedly performed 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 still does not reach the target intake air amount Vt even when the opening of the ETV 14 by the throttle actuator 14a reaches the maximum value, the VVT 30 is operated to retard the closing timing of the intake valve 5. By doing so, the intake stroke is substantially increased to compensate for the insufficient intake amount. When the closing timing of the intake valve 5 is retarded, the closing timing is at the vicinity of the bottom dead center at the maximum.
[0042]
As described above, in the high expansion ratio engine according to the present embodiment, when the engine is in an operating state in which the intake air amount is insufficient (that is, when the engine 1 is in an acceleration transient or operating in a low / medium speed range), first the throttle actuator 14a is used to increase the opening of the ETV 14 to increase the amount of intake, and when the amount of intake is still insufficient even when the opening of the ETV 14 is maximized, the amount of intake is increased by operating the VVT 30. . In addition, when the shortage of the intake air amount can be solved by the opening degree control of the ETV 14, the operation control of the VVT 30 is naturally not executed.
[0043]
Next, the reason why the opening control of the ETV 14 is preferentially executed and the operation control of the VVT 30 is subsequently executed when increasing the intake air amount will be described.
As described above, in a mirror 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. The improvement of thermal efficiency is aimed at. Specifically, the valve closing timing of the intake valve 5 is moved away from the bottom dead center as much as possible to reduce the substantial intake stroke, thereby reducing the geometric compression ratio ρ than the expansion ratio ε.
[0044]
Therefore, if the intake amount is insufficient and the VVT 30 is operated to delay the closing timing of the intake valve 5 to near the bottom dead center, the intake amount can be increased, but during this time, the cycle is close to the Otto cycle. Thus, the original advantage of the mirror cycle is lost. That is, in this case, the pump loss increases relative to the mirror 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 the direction of increasing the throttle opening, so that the pumping loss is reduced. 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, when the engine 1 is in an operating state where the intake amount is insufficient, such as during acceleration transients or when operating in the low / medium speed range, first, the opening of the ETV 14 is positively activated. 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 formed on the camshaft 31 and is rotated according to the rotation of the crankshaft. , 32b and rocker arms 33a, 33b driven by these cams 32a, 32b. Both of these rocker arms 33a and 33b do not contact the intake valves 5 and 5, and are configured as sub-rocker arms indirectly related to the opening and closing drive of the intake valves 5 and 5. Between these sub rocker arms 33a and 33b, there is provided a main rocker arm 33c which is in contact with the stem end portion of the intake valves 5 and 5 and directly related to the opening and closing drive of the intake valves 5 and 5.
[0048]
Further, one cam 32a has a cam profile suitable for a mirror cycle for early intake closing, and the other cam 32b has a cam profile that retards the valve closing timing than the one cam 32a. ing.
Here, the main rocker arm 33 c is formed integrally with the rocker shaft 34 and is configured to be swingable together with the rocker shaft 34. The tip of the main rocker arm 33c is in contact with the stem upper end of the intake valves 5 and 5.
[0049]
Further, the two sub rocker arms 33a and 33b are pivotally supported so as to be rotatable relative to the rocker shaft 34 (that is, the main rocker arm 33c).
Further, as shown in FIG. 2B, between the sub rocker arms 33a and 33b and the rocker shaft 34, the sub rocker arms 33a and 33b are rotatable with respect to the rocker shaft 34, and the main rocker arm 33c and Hydraulic piston mechanisms 36a and 36b are provided that can switch between a mode in which no linkage operation is performed (non-linkage mode) and a mode in which the sub-rocker arms 33a and 33b rotate integrally with the rocker shaft 34 and link with the main rocker arm 33c (linkage mode). ing.
[0050]
In addition, oil passages 34a and 34b are formed inside the rocker shaft 34, and the operation of the hydraulic piston mechanisms 36a and 36b is switched by the hydraulic oil supplied and discharged from the oil passages 34a and 34b. ing. For example, when hydraulic fluid is supplied from the oil passages 34a and 34b to the piston mechanisms 36a and 36b, the piston 37a is driven to the base end side in the piston mechanism 36a, and the tip of the piston 37a is detached from the hole 38a. On the other hand, in the piston mechanism 36b, the piston 37b is driven to the tip end side, and the tip end portion of the piston 37b is fitted into the hole 38b.
[0051]
When the piston 37b is inserted into the hole 38b, the sub rocker arm 33b rotates integrally with the rocker shaft 34 to be linked to the main rocker arm 33c (linkage mode), and the piston 37a is detached from the hole 38a. The rocker arm 33a is rotatable with respect to the rocker shaft 34, and is in a mode in which the rocker arm 33a is not linked to the main rocker arm 33c (non-linked mode).
[0052]
Further, the supply state of the above-described hydraulic oil is controlled by the ECU 40, thereby appropriately switching between the linkage mode and the non-linkage mode of the sub rocker arms 33b and 33a, and the closing timing of the intake valve 5 is set. Can be changed.
Since the high expansion ratio cycle engine according to the embodiment of the present invention is configured as described above, the ECU 40 is operated by the ECU 40 during acceleration transient based on information from the engine speed sensor 3 and the accelerator position sensor 4. In a state where there is no operation in the high speed range, the sub rocker arm 33a is switched to a mode in which the main rocker arm 33c is linked to the main rocker arm 33c.
[0053]
Therefore, in this case, the intake valve 5 is driven to open and close by a cam 32a having a cam profile suitable for a mirror cycle for 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, the intake valve 5 is closed at a predetermined timing before the bottom dead center (BDC) (see point b in FIG. 5), and the substantial intake stroke is thereby completed.
[0054]
Then, the intake air amount is reduced by closing the intake valve 5 at a timing much earlier than the piston reaches the bottom dead center in this way, thereby reducing 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 is relatively larger than the substantial compression stroke, so that the expansion ratio ε> the geometric compression ratio ρ. As a result, the 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).
[0055]
On the other hand, when the ECU 40 determines that the engine 1 is in an acceleration transient state or is operating in a low / medium speed range based on information from the engine speed sensor 3 and the accelerator position sensor 4, a target intake air amount setting is performed. The target value (target intake air amount) Vt set by the means 43 and the actual intake air amount (actual intake air amount) Vr detected by the AFS 18 are compared by the comparison means 44. 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 throttle opening setting means 46 performs the opening control of the ETV 14.
[0056]
That is, in this case, in order to increase the intake air amount, 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 is increased by the predetermined opening Δθ. Then, the actual intake air amount Vr and the target intake air amount Vt are again compared by the comparison means 4 and if the actual intake air amount Vr is still less than or equal to the target intake air amount Vt, the opening degree 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 degree control of the ETV 14 is executed so that the actual intake air amount Vr and the target intake air amount Vt coincide.
[0057]
If the actual intake air amount Vr does not reach the target intake air amount Vt even when the opening of the ETV 14 reaches the maximum value, the VVT 30 is operated. Specifically, the linkage 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 is linked to the main rocker arm 33c.
[0058]
Therefore, in this case, the intake valve 5 is driven to open and close by the cam 32b whose valve closing timing is set to the retard side of the mirror cycle of the early intake air 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 (see point b in FIG. 5) before the bottom dead center (BDC). Even so, the intake valve 5 is kept open. Then, the intake valve 5 is closed in the vicinity of the bottom dead center, and as much intake air flows into the cylinder as the valve closing timing is retarded.
[0059]
As a result, insufficient intake air can be secured during operation in the low / medium speed range or during acceleration transition, and a reduction in output torque can be prevented.
Hereinafter, the operation of the present invention will be described based on the flowchart of FIG. 3. First, in step S1, information from each sensor is captured. 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 a low / medium speed range or the engine 1 is in an acceleration transient state. If the engine 1 is operating in the low / medium speed range, or if the engine 1 is in an acceleration transition state, the process proceeds to step S3, and if not, the process 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 at the time of acceleration transient, it is considered that the intake air amount has decreased, and is detected by the AFS18. The actual intake air amount Vr is compared with the target intake air amount Vt set by the target intake air amount setting means 43 to determine whether or not 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 less than or equal to 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. 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. In step S6, it is determined whether or not the throttle opening is maximum. If the throttle opening is not maximum, the process returns to step S4, and the processes in steps S4 and S5 are repeated.
[0063]
Further, if it is determined in step S6 that the throttle opening is the maximum, it becomes a limit state in which the intake amount cannot be increased by the ETV 14 any more. 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 amount.
Therefore, according to the high expansion ratio cycle engine according to an embodiment of the present invention, when the intake air amount until the boost pressure rises during acceleration transient rises is small, the ETV 14 and the ETV 14 Since the operation of the VVT 30 is controlled, a high compression ratio can be achieved, and a shortage of output torque due to a decrease in the combustion amount can be eliminated and sufficient acceleration can be obtained. Further, although the boost pressure is low and the intake air amount is still insufficient in the low / medium speed region, the operation of the ETV 14 and VVT 30 is controlled so as to increase the intake air amount as described above, thereby reducing the combustion amount. There is an advantage that deficiency in output torque can be solved 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 into 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 degree control of the ETV 14 is preferentially executed over the operation control of the VVT 30, and then the operation control of the VVT 30 is executed, so that a 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 consumption 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 the direction of increasing the throttle opening, so that there is an advantage that the pumping loss can be reduced.
[0065]
In addition, this invention is not limited to the thing of the above-mentioned embodiment. For example, in the above-described embodiment, the case of applying the inspiratory early closing type mirror cycle has been described, but the present invention may be applied to the inspiratory late closing type mirror cycle (see the acupressure diagram in FIG. 6). In this case, when it is determined that the engine is in an acceleration transition or operation in a low / medium speed range, it may be controlled to advance the closing timing of the intake valve 5 so that the intake 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 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. 4 may be applied.
[0067]
Needless to say, the engine to which the present invention is applied is not limited to the in-cylinder injection type spark ignition engine as described above, but can be applied to a port injection type engine.
In the above-described embodiment, it is determined whether or not the intake air amount is the target intake air amount using information from the AFS (air flow sensor), but a pressure sensor (boost pressure sensor) is disposed downstream of the turbocharger. ) To determine whether the actual intake air pressure is larger than the target intake air pressure based on the boost pressure obtained by the pressure sensor, and thereby determine whether the intake air amount is less than the target value. Good.
[0068]
【The invention's effect】
As described above in detail, according to the high expansion ratio cycle engine of the present invention, the drive-by-wire mechanism increases the intake air amount when the intake air amount until the boost pressure rises during acceleration transient rises is small. Since the throttle opening degree and the intake valve closing timing are controlled, it is possible to prevent an output torque shortage due to a decrease in combustion amount. As a result, sufficient acceleration can be obtained even during acceleration transition, and drivability is improved. In addition, since the technology of the drive-by-wire mechanism and the variable valve timing mechanism that are already in 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 operated over the variable valve timing mechanism to increase the intake air amount, the pumping loss can be reduced, and the high expansion ratio can be maintained as much as possible, resulting in a decrease in thermal efficiency. Can be prevented. Therefore, there is an advantage that both improvement in fuel consumption 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 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 operation region where the supercharging pressure in the low / medium speed region becomes low. Therefore, deficiency in output torque due to a decrease in the combustion amount can be solved, and drivability is improved. In addition, since the technology of the drive-by-wire mechanism and the variable valve timing mechanism that are already in 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 operated over the variable valve timing mechanism to increase the intake air amount, the pumping loss can be reduced, and the high expansion ratio can be maintained as much as possible, resulting in a decrease in thermal efficiency. Can be prevented. Therefore, there is an advantage that both improvement in fuel consumption 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 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 the 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 a variable valve timing mechanism applied to the present invention.
FIG. 5 is a shiatsu 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 Airflow 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 Driving speed region determination means
43 Target intake air amount setting means
44 Comparison means

Claims (5)

In a high expansion ratio cycle engine with an expansion ratio set larger than the compression ratio and a supercharger,
An acceleration transient judging means for judging an acceleration transient of the engine;
A variable valve timing mechanism capable of changing the closing timing of the intake valve of the engine;
A drive-by-wire mechanism electrically connected to the accelerator pedal and capable of changing the throttle opening;
Control means for controlling the operation of the variable valve timing mechanism and the drive-by-wire mechanism;
When the acceleration transient determination means determines the acceleration transient time, the operation of the drive-by-wire mechanism is controlled so that the amount of intake air increases, and the intake-air mechanism is activated even after the drive-by-wire mechanism is activated. When it is determined that the amount of air is insufficient, the operation of the variable valve timing mechanism is controlled so that the amount of intake air is increased. In a high expansion ratio cycle engine with an expansion ratio set larger than the compression ratio and a supercharger,
An operating speed area determining means for determining an operating speed area of the engine;
A variable valve timing mechanism capable of changing the closing timing of the intake valve of the engine;
A drive-by-wire mechanism electrically connected to the accelerator pedal and capable of changing the throttle opening;
Control means for controlling the operation of the variable valve timing mechanism and the drive-by-wire mechanism;
When the operating speed region determining means determines that the operating speed region of the engine is a low / medium speed region, the operation of the drive-by-wire mechanism is controlled so that the intake air amount increases, and the drive-by-wire mechanism When the intake air amount is determined to be insufficient even after the operation of the engine, the operation of the variable valve timing mechanism is controlled so that the intake air amount increases. engine. 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. The high expansion ratio cycle engine according to claim 1 or 2. The engine is an intake valve early closing type high expansion ratio cycle engine configured to close an intake valve in the middle of an intake stroke so that an expansion ratio is larger than a compression ratio, the variable valve The high expansion ratio cycle according to any one of claims 1 to 3, wherein the intake air amount is increased by retarding the closing timing of the intake valve by a timing mechanism. engine. The engine is an intake valve slow closing type high expansion ratio cycle engine configured to close the intake valve in the middle of a compression stroke so that the expansion ratio is larger than the compression ratio, the variable valve The high expansion ratio cycle according to any one of claims 1 to 3, wherein the intake amount is increased by advancing the closing timing of the intake valve by a timing mechanism. engine.

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