JP4089407B2 - High expansion ratio cycle engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a high expansion ratio cycle engine in which an expansion ratio is set larger than a compression ratio.
[0002]
[Prior art]
2. Description of the Related Art Otto-cycle gasoline engines having four strokes (intake, compression, expansion, and exhaust) have been widely used as driving sources for vehicles such as automobiles. In such a gasoline engine, the thermal efficiency is improved by various improvements and devices, but there is a demand for further improving the thermal efficiency.
[0003]
In order to improve thermal efficiency, it is known that the expansion ratio can be increased by extending the stroke when the engine is expanded. However, in the Otto cycle, the piston stroke is the same in each stroke, and the expansion ratio and compression are the same. The ratio is equal. For this reason, when the expansion ratio is increased, the compression ratio is also increased, and the air-fuel mixture is ignited early in the combustion chamber due to the heat generated by the compression, and knocking is likely to occur. Therefore, even if the expansion ratio (= compression ratio) is greatly increased in order to improve the thermal efficiency, the limit is low, and it is difficult to substantially increase the expansion ratio.
[0004]
Therefore, conventionally, the intake amount is limited by greatly advancing the closing timing of the intake valve or delaying the closing timing of the intake valve substantially, and the expansion ratio is substantially reduced by the compression ratio. An engine with a high expansion ratio cycle (hereinafter also referred to as Miller cycle or Atkinson cycle), which is set to be larger than that, has been put into practical use. Moreover, as a technique regarding such a mirror cycle engine, for example, Patent Document 1 and Patent Document 2 disclose the technique.
[0005]
Hereinafter, an engine to which such a mirror cycle is applied will be briefly described with reference to the acupressure diagrams of FIGS. Among these, FIG. 6 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. 7 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. 6. 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.
In addition, the intake valve slow closing type mirror cycle shown in FIG. 7 also 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 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 / medium speed range is low. 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 expansion 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. If it is determined that the state is an acceleration transient, the operation of the supercharging pressure changing means is first controlled so that the intake air amount increases. Then, even after the operation control of the supercharging pressure changing means, if the intake air amount is still insufficient, the operation of the variable valve timing mechanism is controlled so that the intake air amount next increases. In other words, when the shortage of intake air is compensated for during acceleration transients, the boost pressure change means is preferentially operated and the boost pressure is changed to increase the intake air amount. If the air intake is insufficient, 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. Further, since the supercharging pressure changing means 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 supercharging pressure changing means is first controlled so that the intake air amount increases. Then, even after the operation control of the supercharging pressure changing means, if the intake air amount is still insufficient, the operation of the variable valve timing mechanism is controlled so that the intake air amount next increases. In other words, when the engine operating range is low and medium speed range, when the shortage of intake air amount is compensated, the boost pressure change means is preferentially operated to increase the intake air amount by changing the boost pressure. If the intake air amount is still insufficient, the variable valve timing mechanism is operated to compensate for the shortage of intake air amount. Therefore, sufficient acceleration can be obtained even during operation in the low and medium speed ranges, and drivability is improved. Further, since the supercharging pressure changing means 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 actual intake air amount detected by the actual intake air amount detection means and the target intake air amount set by the target intake air amount setting means are compared by the comparison means, and the actual intake air amount is the target intake air amount. It is configured to determine that the intake air amount is insufficient if the following is true.
Further, preferably, the supercharger is a turbocharger with a variable nozzle vane, and the intake air amount is increased by changing the opening degree of the nozzle vane to increase the supercharging pressure. Further, the variable valve timing mechanism is operated so that the intake air amount increases when the intake air amount is insufficient even when the opening degree change amount of the nozzle vane is maximized.
[0020]
The engine is a high expansion ratio cycle engine of an intake valve early closing type in which the expansion ratio is made larger than the compression ratio by closing the intake valve in the middle of the intake stroke, and the variable valve timing The mechanism increases the intake amount by retarding the closing timing of the intake valve.
The engine is an intake valve slow closing type high expansion ratio cycle engine configured to make the expansion ratio larger than the compression ratio by closing the intake valve in the middle of the compression stroke, and the variable valve timing The mechanism increases the intake amount 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, a throttle position sensor (TPS) 16 that detects the opening of the throttle valve 14, and intake air. An intake air amount sensor (air flow sensor or AFS) 18 is provided as actual intake air amount detection means for measuring the amount.
[0025]
Here, the ETV 14 includes a throttle actuator 14a, and the throttle opening is changed by the throttle actuator 14a. The operation of the throttle actuator 14a is controlled based on a control signal from an ECU (control means) 40, which will be described later, and usually has a throttle opening corresponding to the depression amount of the accelerator pedal of the driver. Thus, the operation of the throttle actuator 14a is controlled.
[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. In this embodiment, the turbocharger 13 is a so-called variable nozzle vane turbocharger that can change the supercharging pressure by changing the opening of a nozzle vane attached to the turbine.
Here, the turbocharger 13 with variable nozzle vanes will be described. As shown in FIG. 3, a plurality of nozzle vanes 13c are arranged at equal intervals around the turbine blade 13b of the turbine 13a. Each nozzle vane 13c is connected to an annular ring 13d disposed coaxially with the turbine 13a. When this annular ring 13d rotates in the direction of the arrow in the figure, the angle of the nozzle vane 13c, that is, the opening degree is changed. It has come to be.
[0027]
An actuator (supercharging pressure changing means) 20 is connected to the annular ring 13d. Here, the actuator 20 is a positive pressure type actuator whose operation state is controlled according to the pressure of the air supplied into the control chamber 20 a, and the angle of the nozzle vane 13 c according to the operation state of the actuator 20. The (opening degree) is adjusted stepwise. Although not shown in detail, the actuator 20 is connected to a high-pressure air passage, and a solenoid valve, for example, is provided on the air passage. The operation of the actuator 20 is controlled by duty-controlling the solenoid valve.
[0028]
The actuator 20 is not limited to such a configuration, and any other configuration may be applied as long as the angle of the nozzle vane can be adjusted continuously or stepwise.
On the other hand, the ECU 40 includes an input / output device, a storage device (ROM, RAM, nonvolatile RAM, etc.), a calculation device (CPU), a timer counter, and the like. Is to be executed.
[0029]
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.
[0030]
Various output devices such as the above-described fuel injection valve 6, actuator 14a of the ETV (throttle valve) 14, and actuator 20 of the turbocharger 13 are connected to the output side of the ECU 40. A control signal from the ECU 40 is input. 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.
[0031]
As a result, an appropriate amount of fuel is injected from the fuel injection valve 6 at an appropriate timing, spark ignition is performed at an appropriate timing by the spark plug, and the ETV 14 is driven to open and close at an appropriate opening at an appropriate timing. It has become so.
Next, the main part of the present invention will be described. The valve mechanism 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. . 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.
[0032]
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 determination 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 the detection information from the AFS 18 You may make it determine based on.
[0033]
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.
[0034]
In addition to the above, the ECU 40 is provided with target intake air amount setting means 43, comparison means 44, and supercharging pressure setting means 45. Among these, the target intake air amount setting means 43 sets a target value Vt of the intake air amount of the engine 1 (hereinafter simply referred to as the intake amount) based on the engine speed Ne, the accelerator pedal depression amount (load) Acc, and the like. For example, the target value Vt is read from a map (not shown).
[0035]
The comparison unit 44 compares the target value (target intake air amount) Vt of the intake air amount set by the target intake air amount setting unit 43 with the actual intake air amount (actual intake air amount) Vr detected by the AFS 18. More specifically, a difference ΔV (= Vr−Vt) between the actual intake air amount Vr and the target intake air amount Vt is calculated.
The supercharging pressure setting means 45 sets the supercharging pressure of the turbocharger 13, and the supercharging pressure of the actuator 20 of the turbocharger 13 is set so as to be the supercharging pressure set by the supercharging pressure setting means 45. The operation is feedback controlled.
[0036]
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 that the engine 1 is present, the supercharging pressure is set to be larger than that during normal operation by the supercharging pressure setting means 45 in order to compensate for the intake air amount deficient in the engine 1.
[0037]
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 supercharging pressure setting means 45 to the actuator 20 so that the current angle of the nozzle vane 13c increases by one step.
[0038]
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.
[0039]
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. .
[0040]
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.
[0041]
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, the angle of the current nozzle vane 13c is increased by one step. The boost pressure is increased. Here, increasing the supercharging pressure means increasing the intake air amount, and the increase in the intake air amount suppresses a decrease in output during acceleration transient or the like.
[0042]
After that, after the opening degree of the nozzle vane 13c is changed, the calculation result of the comparison unit 44 is referred to again. If the actual intake air amount Vr reaches the target intake air amount Vt, the opening degree of the nozzle vane 13c is maintained and the actual intake air is obtained. If the amount Vr does not reach the target intake air amount Vt, the opening degree of the one-stage nozzle vane 13c is further increased. Such control is repeated, and the opening degree control (supercharging pressure control) of the nozzle vane 13c is executed so that the actual intake air amount Vr matches the target intake air amount Vt.
[0043]
If the actual intake air amount Vr still does not reach the target intake air amount Vt even if the opening degree of the nozzle vane 13c reaches the maximum value, the valve closing timing of the intake valve 5 is retarded by operating the VVT 30. 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.
[0044]
As described above, in the high expansion ratio engine according to the present embodiment, when the engine is in an operation state in which the intake air amount is insufficient (that is, when the engine 1 is in an acceleration transient or operation in a low / medium speed region), first, the turbocharger. 13 is increased to increase the intake air amount. Even when the turbocharger 13 has the maximum supercharging pressure, if the intake air amount is still insufficient, the VVT 30 is operated to increase the intake air amount. ing. In addition, when the shortage of the intake air amount can be solved by the supercharging pressure control of the turbocharger 13, the operation control of the VVT 30 is not executed as a matter of course.
[0045]
Next, the reason for preferentially executing the supercharging pressure control of the turbocharger 13 and then executing the operation control of the VVT 30 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.
[0046]
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.
[0047]
On the other hand, the turbocharger 13 primarily uses the exhaust energy to increase the output, and even if the supercharging pressure control is executed, the pump loss increases or the thermal efficiency decreases. Such a problem does not occur.
Therefore, in the high expansion ratio engine according to the present embodiment, in an operating state where the intake amount is insufficient, such as during acceleration transition of the engine 1 or during operation in the low / medium speed range, first, the turbocharger 13 is actively activated. The intake pressure is increased by controlling the supercharging pressure. If the intake amount is still insufficient, the VVT 30 is operated to increase the intake amount.
[0048]
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.
[0049]
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.
[0050]
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.
[0051]
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.
[0052]
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).
[0053]
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.
[0054]
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. 6), whereby the substantial intake stroke is completed.
[0055]
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).
[0056]
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 less than or equal to the target intake air amount Vt, the supercharging pressure control of the turbocharger 13 is executed by the supercharging pressure setting means 45.
[0057]
That is, in this case, a control signal is output from the supercharging pressure setting means 45 to the actuator 20 so that the opening degree of the variable nozzle vane 13c of the turbocharger 13 is increased by one step in order to increase the intake air amount. After that, the comparison means 44 compares the actual intake air amount Vr with the target intake air amount Vt. 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 nozzle vane 13c is further increased. The actual intake air amount Vr is increased. Then, such control is repeated, and the opening degree control of the nozzle vane 13c is executed so that the actual intake air amount Vr and the target intake air amount Vt coincide with each other.
[0058]
If the actual intake air amount Vr is less than the target intake air amount Vt even when the opening degree of the nozzle vane 13c 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 other sub-rocker arm 33b is switched to a mode in which the linkage operation is performed with the main rocker arm 33c.
[0059]
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. 6) 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.
[0060]
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. 4. 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.
[0061]
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.
[0062]
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.
[0063]
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, and the angle of the variable nozzle vane 13c of the turbocharger 13 is increased by one step in order to increase the supercharging pressure. The The intake air amount can be increased by increasing the supercharging pressure in this way.
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 routine returns and the actual intake air amount Vr becomes the target intake air amount Vt. If not, the process proceeds to step S6. In step S6, it is determined whether or not the opening degree of the nozzle vane 13c is maximum. If the opening degree is not maximum, the process returns to step S4, and the processes in steps S4 and S5 are repeated again.
[0064]
Further, if it is determined in step S6 that the opening degree of the nozzle vane 13c is maximum, the turbocharger 13 is in a limit state where the intake air amount cannot be increased. 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.
[0065]
Therefore, according to the high expansion ratio cycle engine of one embodiment of the present invention, when the intake air amount is small until the boost pressure rises during acceleration transient, the turbocharger is increased so that the intake air amount increases. 13 and VVT 30 are controlled, so that 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 supercharging pressure is low and the intake amount is still insufficient in the low and medium speed ranges, the operation of the turbocharger 13 and the VVT 30 is controlled so as to increase the intake amount as described above, thereby reducing the combustion amount. There is an advantage that deficiency in output torque due to the reduction can be solved and drivability is improved. In addition, since the technology of a variable nozzle vane turbocharger and a 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.
[0066]
In addition, as described above, when the intake air amount is to be increased, the supercharging pressure control of the turbocharger 13 is preferentially executed over the operation control of the VVT 30, and then the operation control of the VVT 30 is executed. Can be maintained, and 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.
[0067]
In addition, this invention is not limited to the thing of the above-mentioned embodiment. For example, in the above-described embodiment, the case where the inspiratory early closing type mirror cycle is applied has been described. However, the present invention may be applied to the inspiratory late closing type mirror cycle (see the acupressure diagram in FIG. 7). 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.
[0068]
Further, the VVT (variable valve timing mechanism) is not limited to the rocker arm switching type as described above, and various other mechanisms can be applied as long as the closing timing of the intake valve 5 can be changed. is there. For example, as the variable valve timing mechanism, an electromagnetic intake valve in which the opening / closing timing and the lift amount can be arbitrarily set by the driving force of the electromagnetic coils 5a and 5b as shown in FIG. 5 may be applied.
[0069]
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.
[0070]
【The invention's effect】
As described above in detail, according to the high expansion ratio cycle engine of the present invention, when the intake air amount until the boost pressure rises at the time of acceleration transient rises, the supercharger increases so that the intake air amount increases. Since the supercharging pressure of the intake air and the closing timing of the intake valve are controlled by this, the output torque shortage due to the decrease in the combustion amount can be prevented. As a result, sufficient acceleration can be obtained even during acceleration transition, and drivability is improved. In addition, since the technology of the supercharger 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. Further, since the supercharging pressure changing means 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. Therefore, there is an advantage that both improvement in fuel efficiency and improvement in drivability can be achieved (claims 1, 5 and 6).
[0071]
Further, according to the high expansion ratio cycle engine of the present invention, the valve closing timing of the intake valve is controlled so that the intake air amount increases in the operation region where the supercharging pressure in the low / medium speed region becomes low. The lack of output torque due to the decrease in the output can be resolved, and drivability is improved. In addition, since the technology of the supercharger 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. Further, since the supercharging pressure changing means 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. Therefore, there is an advantage that both improvement in fuel consumption and improvement in drivability can be achieved (claims 2, 5, 6).
In addition, according to the high expansion ratio cycle engine of the present invention, there is an advantage that the intake air amount can be easily changed by changing the opening degree of the nozzle vane (claims 3 and 4).
[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 schematic diagram showing a main configuration of the high expansion ratio cycle engine according to the first embodiment of the present invention.
FIG. 4 is a flowchart illustrating the operation of the high expansion ratio cycle engine according to the first embodiment of the present invention.
FIG. 5 is a schematic diagram for explaining another example of the variable valve timing mechanism applied to the present invention.
FIG. 6 is a shiatsu diagram illustrating an example of a conventional high expansion ratio cycle engine.
FIG. 7 is an acupressure diagram illustrating another example of a conventional high expansion ratio cycle engine.
[Explanation of symbols]
1 engine
5 Intake valve
13 Turbocharger (supercharger)
14 ETV (drive-by-wire slot valve)
18 Airflow sensor or AFS (actual intake air amount detection means)
20 Actuator (Supercharging pressure changing 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 (6)

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 supercharging pressure changing means capable of changing the supercharging pressure of the intake air by the supercharger;
Control means for controlling the operation of the variable valve timing mechanism and the supercharging pressure changing means,
When the acceleration transient determining means determines the acceleration transient time, the operation of the supercharging pressure changing means is controlled so that the intake air amount increases, and after the supercharging pressure changing means is operated. If it is determined that the intake air amount is insufficient, the operation of the variable valve timing mechanism is controlled so that the intake air amount increases. 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 supercharging pressure changing means capable of changing the supercharging pressure of the intake air by the supercharger;
Control means for controlling the operation of the variable valve timing mechanism and the supercharging pressure changing means,
When the operating speed region determining means determines that the engine operating speed region is a low / medium speed region, the operation of the supercharging pressure changing means is controlled so that the intake air amount increases, and When it is determined that the intake air amount is insufficient even after the operation of the supply pressure changing means, the operation of the variable valve timing mechanism is controlled so that the intake air amount increases. High expansion ratio cycle engine. The turbocharger is a turbocharger with a variable nozzle vane capable of changing a supercharging pressure by changing an opening degree of a nozzle vane attached to the turbine,
The high expansion ratio cycle engine according to claim 1 or 2, wherein the intake air amount is increased by changing an opening of the nozzle vane so that the supercharging pressure increases. 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 opening degree change amount of the nozzle vane is maximized. Item 4. The high expansion ratio cycle engine according to Item 3. 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 4, wherein the timing mechanism is configured to increase the intake air amount by retarding the closing timing of the intake valve. 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 4, wherein the timing mechanism is configured to increase the intake amount by advancing the closing timing of the intake valve. engine.

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