JP2002332877A - Four-stroke engine for car - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase reliability of an engine by suppressing the occurrence of knockings in a high load and high speed operation, without impairing layer combustibility, when the engine is running at a low load and a low speed. SOLUTION: In this four-stroke engine for a car, having a phase type valve timing variable device 13 for varying the valve-opening and closing timings of an intake valve 9, while maintaining the valve opening period thereof to be fixed, a valve timing control means 42 is installed to set the opening timing of the intake valve in the high-load and high-speed engine operating range to a time after a top dead center of intake air, when the amount of gas is blown out to an intake port to almost 0 by he opening of the intake valve, and set the intake valve closing timing in the operating range to a timing which is delayed by a specified value or more than the bottom dead center of the intake air.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a four-stroke engine for a vehicle equipped with a phase-type variable valve timing device for varying the opening / closing timing of an intake valve while keeping the opening period of the intake valve constant.

[0002]

2. Description of the Related Art Conventionally, for example, Japanese Patent Laid-Open No. 61-187526
As shown in the publication, in an engine equipped with a supercharger, a variable valve timing mechanism for controlling a valve timing of an intake valve, a unit for detecting an operating condition of the supercharger, and a signal from the detection unit. Means for calculating the valve timing of the intake valve; and means for driving the variable valve timing mechanism so as to obtain the calculated valve timing. The detection means detects the engine speed, the supercharging pressure or the intake air temperature. And operating the variable valve timing mechanism so as to obtain the calculated delay amount by calculating the delay amount of the valve timing based on the condition factor. A valve timing control device for a supercharged engine with such a configuration is known.

[0003]

As described in the above publication, the delay amount of the valve timing is determined based on a turbocharger operating condition factor such as an engine speed, a supercharging pressure or an intake air temperature detected by the detecting means. In the case of controlling the valve, for example, during high-speed rotation in a high-load (high-load) region where the supercharging pressure is high, the valve timing of the intake valve is delayed as compared with the normal time, thereby increasing the geometric compression ratio. As a result, the effective compression ratio can be appropriately suppressed while increasing the expansion ratio. Therefore, it is possible to suppress the rise in the temperature of the combustion chamber at the compression top dead center, thereby preventing the occurrence of knocking.

However, in a four-stroke engine for an automobile equipped with a phase-type variable valve timing device that varies the opening and closing timing of the intake valve while keeping the opening period of the intake valve constant, as described above, the engine has a high load and a high rotational speed. When the intake valve closing timing is sometimes delayed, the intake valve opening timing is also delayed correspondingly. And
When the delay in the opening timing of the intake valve increases, the pressure in the combustion chamber decreases during the delay, so that a large amount of intake air flows into the combustion chamber at a high speed simultaneously with the opening of the intake valve. It is inevitable that the pre-compression temperature rises, and as a result, the compression top dead center temperature rises and knocking easily occurs.

In the operating state where the pre-compression temperature of the intake air increases as described above, the compression top dead center temperature cannot be reduced even if the effective compression ratio is reduced, and the knock resistance of the engine can be improved. Because it is not possible to extend the valve opening period of the intake valve without delaying the intake valve opening timing during high load and high speed rotation, it is also possible to delay the intake valve closing timing to prevent the intake air pre-compression temperature from rising. Conceivable. However, in the case of such a configuration, there is a problem that stratified combustion that is advantageous in terms of fuel efficiency cannot be performed in a low-load (partial load) and low-speed operation region of the engine.

That is, when the engine that performs stratified combustion with the air-fuel ratio leaner than the stoichiometric air-fuel ratio is operated at a low load and at a low speed, the return of intake air due to the intake valve closing timing being too late is suppressed. In order to be suitable for stratified charge combustion, it is necessary to advance the intake valve closing timing as compared with high load and high speed rotation. In this case, if the opening period of the intake valve is long, the opening timing of the intake valve is excessively advanced in accordance with the advance of the closing timing of the intake valve, and a large amount of burned gas is generated when the intake valve is opened. The fuel may be blown back to the intake port and combustion stability may be impaired.

Therefore, in a four-stroke engine for an automobile equipped with the above-described phase type variable valve timing device, stratified combustion can be appropriately performed without impairing combustion stability at low load and low speed rotation. In order to achieve this, the opening period of the intake valve is relatively short, for example, 220 d
It is necessary to prevent the intake valve opening timing from being excessively advanced when the intake valve closing timing is advanced by setting it to about EG to 230 deg.

On the other hand, by using a phase-type variable valve timing device in which the closing period of the intake valve is set to be short, the intake valve closing timing at the time of high load and high speed rotation of the engine is adjusted in order to appropriately suppress the effective compression ratio. When the control for retarding is executed, the opening timing of the intake valve is also retarded at the same time, so that a large amount of intake air flows into the combustion chamber at a high speed as described above, and the pre-compression temperature rises, and the compression top dead center There is a problem that knocking is likely to occur due to an increase in the temperature of the combustion chamber in the above, and it has been desired to prevent such adverse effects.

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention provides a four-stroke engine for an automobile equipped with a phase-type variable valve timing device that varies the opening / closing timing of an intake valve while keeping the opening period of the intake valve constant. -To provide a four-stroke engine for an automobile that can suppress the occurrence of knocking at the time of high load and high speed rotation, enhance engine reliability, and improve engine output without impairing stratified combustion at low speed rotation. Things.

[0010]

SUMMARY OF THE INVENTION The present invention relates to a four-stroke engine for an automobile having a phase-type variable valve timing device for varying the opening / closing timing of an intake valve while keeping the opening period of the intake valve constant. The intake valve opening timing in the load and high-speed operation region is set to a time after the intake top dead center and the amount of gas blown back to the intake port by opening the intake valve becomes substantially zero. Valve timing control means for setting the valve closing timing to a timing later than the intake bottom dead center by a predetermined value or more is provided.

According to the present invention, when the engine is in the high-load and high-speed operation region, the opening timing of the intake valve and the closing timing of the intake valve are set to the above-described timings, so that the opening period of the intake valve can be reduced. Without increasing the length, it is possible to prevent a rise in the pre-compression temperature of the intake air due to a large amount of intake air flowing into the combustion chamber at a high speed when the intake valve is opened,
Even when the geometric compression ratio is considerably high, the effective compression ratio is appropriately suppressed and the temperature rise due to the compression work inside the engine is suppressed, so that the occurrence of knocking is effectively prevented. .

In the engine of the present invention, the turbocharger, a bypass passage for bypassing the turbine of the turbocharger, a wastegate valve for opening and closing the bypass passage, and the turbocharger are supercharged by the turbocharger. Preferably, an intercooler for cooling the intake air is provided, and the control of the opening and closing timing of the intake valve by the valve timing control means is performed in an operation range from the vicinity of an intercept point where the wastegate valve is opened to a high-speed rotation side.

With this arrangement, when the engine is in the high-load and high-speed operation range, the control of the intake valve opening / closing timing by the valve timing control means is executed, and the supercharging is performed by the turbocharger. The intake air is supplied to the combustion chamber in a state of being cooled by the intercooler, thereby suppressing an increase in the compression top dead center temperature, and reducing the intake charge due to the delay of the intake valve closing timing. Since the minute is supplemented by the supercharging by the turbocharger, a decrease in engine output due to an insufficient amount of intake air is effectively prevented.

It is preferable that the valve timing control means controls the opening / closing timing of the intake valve at high load and high speed rotation in an operation region on the high speed rotation side of the intercept point.

With this configuration, the control for delaying the opening / closing timing of the intake valve to the above timing is performed in a state where the turbocharger has a surplus power, so that the closing timing of the intake valve is retarded. The decrease in the amount of intake air due to this is effectively compensated for by the supercharging by the turbocharger, and the decrease in engine output due to the insufficient intake air intake is reliably prevented.

In the operating range from the low-speed rotation side to the high-speed rotation side with respect to the intercept point, the valve timing control means controls the intake valve opening / closing timing at the time of high load and high speed rotation. The intake passage may be configured such that a dynamic effect of the intake occurs.

With this configuration, on the low-speed rotation side of the intercept point where there is no excess supercharging force by the turbocharger, the decrease in the amount of intake air due to the delay of the intake valve closing timing is equal to the above-mentioned amount. Since it is compensated by the pulsation effect of the intake air, it is possible to effectively prevent the output from decreasing due to the insufficient filling of the intake air.

Further, it is preferable that the exhaust valve closing timing at the time of high load and high speed rotation of the engine is set before the intake top dead center.

With this arrangement, when the engine is in the high-load and high-speed operation region, the exhaust valve is closed before the intake top dead center, and the low-temperature burned gas remaining in the combustion chamber is used. Since the internal EGR effect is obtained, the temperature rise in the combustion chamber is further suppressed, and the occurrence of knocking is reliably prevented.

[0020]

FIG. 1 schematically shows the entire structure of a four-stroke engine for an automobile to which the present invention is applied. In this figure, reference numeral 1 denotes an engine body, which has a plurality of cylinders, each of which has a combustion chamber 5 formed above a piston 4 inserted into a cylinder bore. The combustion chamber 5 has an intake port 7 and an exhaust port 8
The ports 7, 8 are opened and closed by an intake valve 9 and an exhaust valve 10.

The intake valve 9 and the exhaust valve 10 are opened and closed by a valve operating mechanism including camshafts 11 and 12 and the like. The valve mechanism for the intake valve 9 and the valve mechanism for the exhaust valve 10 are respectively provided with variable valve timing devices 13 and 14 that can change the valve opening / closing timing. The variable valve timing devices 13 and 14 are provided between a cam pulley and a camshaft interlocking with the crankshaft, and change the phase of the camshaft with respect to the crankshaft so that the valve opening period and the opening timing and the closing time are kept constant. It is configured so that the time can be changed. In addition,
Since the variable valve timing devices 13 and 14 are conventionally known in the art, the description of the specific structure thereof will be omitted.

At the center of the combustion chamber 5, a spark plug 16
Is disposed, and the tip of the plug faces the combustion chamber 5.
Further, the front end of the injector 18 faces the combustion chamber 5 from the side, and the fuel is directly injected from the injector 18 into the combustion chamber 5.

An intake passage 20 and an exhaust passage 30 are connected to the engine body 1. The intake passage 20
Is provided with an air cleaner 21, an air flow sensor 22, and a throttle valve 23 in this order from the upstream side.
The throttle valve 23 is mechanically connected to an unillustrated accelerator pedal, and is opened to an opening degree corresponding to the accelerator pedal depression amount. A throttle opening sensor 25 for detecting the opening of the throttle valve 23 is provided.

In the exhaust passage 30, an O ₂ sensor 31 for detecting the air-fuel ratio by detecting the oxygen concentration in the exhaust gas is provided, and a catalyst 32 for purifying the exhaust gas is provided downstream of the O ₂ sensor 31. . The catalyst 32 may be constituted by a three-way catalyst. However, in order to enhance the purification performance when the air-fuel ratio is lean and the stratification operation is performed, even when the air-fuel ratio is under a condition leaner than the stoichiometric air-fuel ratio. It is desirable to use a catalyst that can effectively purify NOx. In the present embodiment, NOx in the exhaust gas is absorbed in an oxygen-excess atmosphere, and when the air-fuel ratio changes from lean to rich and the oxygen concentration decreases, the absorbed NOx is released, and A lean NOx catalyst that reduces NOx with a reducing material such as CO is used.

Further, the engine is provided with a turbocharger 50 having a compressor 51 provided in the intake passage 20, a turbine 52 provided in the exhaust passage 30, and a shaft 53 connecting the two. . This turbocharger 50
Is configured such that the turbine 52 is rotated by the exhaust gas flow, and the compressor 51 is rotated in conjunction therewith, thereby supercharging the intake air. The intake passage 20
An intercooler 55 is provided on the downstream side of the installation part of the compressor 51 in FIG. Further, the exhaust passage 30 is provided with a wastegate passage 56 that bypasses a portion where the turbine 52 is installed.
6 is provided with a wastegate valve 57.

In FIG. 1, reference numeral 40 denotes a control unit (ECU) for controlling the engine. This ECU 4
0, a signal from the air flow sensor 22, the throttle opening sensor 25, and the O ₂ sensor 31 are input, and a crank angle signal for detecting an engine speed and the like is input from a crank angle sensor 35. Signals from a water temperature sensor 36 for detecting the temperature of the cooling water are also input.

A signal for controlling fuel injection is output from the ECU 40 to the injector 18 and a signal for controlling the fuel injection is output to the variable valve timing devices 13 and 14. An opening / closing drive signal is output to the actuator of the valve 57.

The above-mentioned ECU 40 is provided with an operating state determining means 4.
1, a valve timing control means 42 and a fuel injection control means 43 are included. The operating state determining means 41 includes:
The operation of the engine is performed based on the engine speed detected by measuring the cycle of the crank angle signal output from the crank angle sensor 35 and the engine load checked by the signals from the air flow sensor 22, the throttle opening sensor 25, and the like. It is configured to determine the state.

The valve timing control means 42 responds to the operation state determined by the operation state determination means 41,
By controlling the variable valve timing devices 13 and 14, the opening and closing timings of the intake valve 11 and the exhaust valve 12 are set and changed as described later.

The fuel injection control means 43 is configured to control the amount and timing of fuel injection from the injector 18 in accordance with the operating state determined by the operating state determining means 41. For example, in a predetermined region on the low-load side of the engine, the air-fuel ratio is made leaner than the stoichiometric air-fuel ratio, and the fuel is injected in the latter half of the compression stroke so that the air-fuel mixture is unevenly distributed around the ignition plug 16 to perform stratified combustion. The fuel injection amount and the injection timing are controlled so that the fuel injection is performed. On the other hand, in an area other than the predetermined area, the air-fuel ratio is set to the stoichiometric air-fuel ratio or a value close to the stoichiometric air-fuel ratio, and the fuel is injected in the intake stroke to diffuse the air-fuel mixture to perform uniform combustion. Control the quantity and injection timing.

FIG. 2 shows a cam lift curve for indicating the opening / closing timing of the intake and exhaust valves.
ExV means an exhaust valve. In addition, InO and InC
Are the opening timing and closing timing of the intake valve InV, ExO and E
xC is the opening timing and closing timing of the exhaust valve ExV. Here, the opening timing InO of the intake valve InV and the exhaust valve ExV,
ExO is defined by the transition point from the constant velocity section to the acceleration section in the cam lift characteristic, and the closing timings InC and ExC of the intake valve InV and the exhaust valve ExV are defined by the transition point from the acceleration section to the constant velocity section in the cam lift characteristic. (See FIG. 3).

In FIG. 2, when the exhaust valve ExV is most advanced within the opening / closing timing variable range, as indicated by the solid line, the closing timing ExC is a predetermined amount before the intake top dead center TDC, and when the exhaust valve ExV is most retarded, as indicated by the broken line. The closing timing ExC is equal to the intake top dead center T
DC, slightly later than DC, and the intake valve InV is slightly ahead of the intake top dead center TDC, as indicated by the broken line when the intake valve InV is most advanced within the opening / closing timing variable range, and is like the solid line when the intake valve InV is most retarded. The opening timing InO is later than the intake top dead center TDC by a predetermined amount.

Therefore, the exhaust valve Ex as shown by the broken line
When V is retarded and the intake valve InV is advanced, there is a slight overlap between the valve opening periods, but when the exhaust valve ExV is advanced and the intake valve InV is retarded as shown by the solid line. , There is no overlap between both valve opening periods, that is, a minus overlap (minus O / L) state.

The intake valve opening / closing timings InO and InC when the engine is in a high-load and high-speed operation region are:
The intake valve opening timing InO is set as shown by the solid line in FIG.
Is retarded by a predetermined amount as compared with the normal time indicated by the broken line, for example, at the time of low load / low speed rotation, and after the intake top dead center TDC, the gas amount blown back to the intake port by opening the intake valve InV becomes substantially zero. Set at a certain point.

That is, when the intake valve opening timing InO is set before the intake top dead center TDC or early after the intake top dead center, the intake valve 9 is operated while the pressure in the combustion chamber 5 is relatively high. As a result, the burned gas in the combustion chamber 5 is blown back to the intake port 7 simultaneously with the opening of the intake valve 9. On the other hand, when the intake valve opening timing InO is set to a relatively late timing after the intake top dead center TDC, the intake valve 9 is opened in a state where the pressure in the combustion chamber 5 is sufficiently low. Therefore, the gas amount blown back to the intake port 7 at the same time when the intake valve is opened becomes zero.

Whether or not the burned gas is returning to the intake port 7 when the intake valve 9 is opened can be detected by detecting the flow rate of the intake air in the intake port 7. For example, FIG. A simulation for detecting how the flow rate of the intake air changes when the intake valve 9 is opened using an engine as shown in FIG.
Data as shown in FIG. 4 was obtained. In the above simulation, the geometric compression ratio was set to a relatively high compression ratio of 10.2, and the engine speed was set to 50, which is the maximum output point.
With the engine load set to 00 rpm and the engine load set to the full load state, the intake valve opening timing InO was variously changed within the range of 0 deg to 40 deg after the top dead center TDC to detect the change state of the intake flow velocity. . The intake air temperature after passing through the intercooler 55 was set to 60 ° C.

Based on the above data, the intake valve opening timing InO is set to a relatively early timing after the intake top dead center TDC (0 deg, 10 d
When it was set to (eg), it was confirmed that the burned gas flowed back to the intake port 7 at the same time as the opening of the intake valve 9, so that the intake flow velocity temporarily increased and then increased. Then, the intake valve opening timing InO is set at the top dead center TDC.
When the time is set at the later 20 deg, the intake valve In
When the V was released, almost no decrease in the intake flow rate was observed, and it was confirmed that the amount of gas blown back to the intake port 7 was substantially zero.

When the intake valve opening timing InO is set to a timing of 30 deg and 40 deg after the intake top dead center TDC, when the intake valve 9 is opened, no decrease in the intake flow velocity is observed, and It was confirmed that the intake air flow rate sharply increased after opening of No. 9. That is, as shown in FIG. 5, when the amount of delay of the intake valve opening timing is increased beyond the point where the amount of gas blown back to the intake port becomes substantially zero (the timing of 20 deg after the intake top dead center), Correspondingly, it was confirmed that the peak value of the flow velocity in the intake port gradually increased. This is considered to be because a large amount of intake air flows into the combustion chamber 5 at a high speed because the intake valve 9 is opened when the pressure in the combustion chamber 5 is sufficiently reduced.

On the other hand, as shown by the solid line in FIG. 2, the intake valve closing timing InC in the operation region where the engine is under high load and high speed rotation is a point in time that is later than the intake bottom dead center BDC by a predetermined value, that is, the intake valve InV Is set to a point at which the expansion ratio becomes larger than the effective compression ratio until the exhaust valve ExV is opened after the valve is closed, and the effective compression ratio is reduced and the expansion ratio is sufficiently ensured. For example, in an engine in which the geometric compression ratio is set to 10.2, the intake valve closing timing InC in the above-described operation region is set to a time point later than the intake bottom dead center BDC by about 60 deg to 70 deg. The effective compression ratio during the intake compression is reduced to a smaller value than the expansion ratio in the expansion stroke.

As described above, the intake valve opening timing InO is set to a time point 20 deg later than the compression top dead center TDC, and the intake valve closing timing InC is set to the compression bottom dead center BDC.
When the time is set to be about 60 deg to 70 deg later than the opening time of the intake valve InV is 220 deg.
A valve mechanism set for a relatively short period of about 230 deg will be used.

The valve timing control means 42
The control of the intake valve opening / closing timing at the time of high load and high speed rotation of the engine is performed on the higher speed side than the intercept point of the turbocharger 50, that is, the operation in which the turbocharger 50 has a surplus power. Performed on the region. The intercept point is a calculated engine rotational speed at which the supercharging capacity of the turbocharger 50 becomes higher than the required supercharging pressure and the wastegate valve 58 is opened, for example, 3
It indicates about 500 rpm.

In the high-load operation range, when the engine speed reaches the intercept point,
The control of the intake valve opening / closing timing by the valve timing control means 42 makes it difficult for intake air to enter the combustion chamber 5 and increases the required supercharging pressure. The waste gate valve 58
Is shifted to a higher rotation speed side than the calculated intercept point on the assumption that the control of the intake valve opening / closing timing is not executed.

Further, the exhaust valve opening / closing timings ExO and ExC in the operating region where the engine is under a high load and high speed rotation are as shown by the solid line in FIG. -It is retarded by a predetermined amount compared to the time of low-speed rotation, and is set before the intake top dead center TDC. As a result, the period from the exhaust valve closing timing ExC to the intake valve opening timing InO is in a minus overlap (minus O / L) state.

As described above, in the four-stroke engine for a vehicle equipped with the phase type variable valve timing device 13 for varying the opening / closing timing of the intake valve 9 while keeping the opening period of the intake valve 9 constant, the engine is operated under high load and high speed rotation. The opening timing InO of the intake valve in the operating region of FIG.
Thereafter, the time when the amount of gas blown back to the intake port 7 by opening of the intake valve 9 becomes substantially zero is set, and the intake valve closing timing InC in the above-mentioned operation region is set to a predetermined value or more than the intake bottom dead center TDC. Since the control to be set at a later time is executed by the valve timing control means 42, the occurrence of knocking is suppressed at the time of high load / high speed rotation without impairing the stratified combustibility at the time of low load / low speed rotation of the engine. The reliability of the engine.

That is, it is effective to lower the compression top dead center temperature in order to suppress the occurrence of knocking at the time of high load and high speed rotation of the engine. The compression top dead center temperature has a lowering effect of the effective compression ratio by delaying the intake valve closing timing InC, that is, a suppression effect of a temperature rise by reducing the compression work inside the engine, and an opening timing of the intake valve. Since it changes under the influence of the adiabatic compression action and the internal EGR caused by retarding the InO, the intake valve is selected by selecting a timing at which the compression top dead center temperature can be effectively reduced in consideration of these. By setting the opening / closing timing, it is possible to suppress the occurrence of knocking.

FIG. 6 shows the influence A due to the effect of lowering the effective compression ratio, the influence B due to the adiabatic compression effect, and the influence due to the internal EGR on the opening / closing timing of the intake valve and the amount of change ΔT _TDC of the compression top dead center temperature. It shows the relationship between the degree C and the sum D of them. From this figure, as the intake valve opening / closing timing is retarded, the degree of influence A due to the effect of lowering the effective compression ratio acts in the direction of decreasing the compression top dead center temperature, and this effect is nonlinear. Increase.

When the amount of retard of the intake valve opening / closing timing reaches a predetermined value, the influence B due to the adiabatic compression action
Acts in the direction of increasing the compression top dead center temperature, and this effect increases nonlinearly as the retard amount increases. This is because the retard amount becomes a predetermined value and the intake valve 9
When the closing timing of the intake valve is further delayed than the timing at which the amount of gas blown back to the intake port 7 becomes substantially zero at the same time as the opening of the intake port 7, the intake air rapidly flows into the combustion chamber 5,
This is because the flow velocity energy of the intake air is converted into heat energy in the combustion chamber.

Incidentally, as the intake valve opening / closing timing is retarded, the inflow of intake air is suppressed, and the required supercharging pressure of the turbocharger 50 increases. Back pressure) is increased by increasing the internal E
Since the GR amount increases, the degree of influence C due to the internal EGR
Acts to increase the compression top dead center temperature. The degree of influence C due to the internal EGR includes the degree of influence A due to the effect of decreasing the effective compression ratio and the degree of influence B due to the adiabatic compression effect.
Therefore, as factors determining the compression top dead center temperature, the degree of influence A due to the effect of decreasing the effective compression ratio and the degree of influence B due to the adiabatic compression action are dominant.

Therefore, as described above, the intake valve opening timing InO in the operating region where the engine is under high load and high speed rotation
Is set after the intake top dead center TDC and when the amount of gas blown back to the intake port 7 by opening the intake valve 9 becomes substantially zero, the influence of the adiabatic compression action is eliminated, and the compression top dead center is eliminated. The rise in point temperature can be suppressed.
Further, by setting the intake valve closing timing InC in the operation region to a timing later than the intake bottom dead center TDC by a predetermined value or more, the compression top dead center temperature is remarkably increased by utilizing the effect of decreasing the effective compression ratio. Because it can be reduced, knocking is effectively prevented and engine reliability is improved even in engines with a high compression ratio in which the geometric compression ratio is set to 9.5 or more to improve thermal efficiency. Can be done.

For example, if the geometric compression ratio of the engine is 1
0.2 and a relatively high compression ratio, and the engine speed
With the maximum output point set to 5000 rpm and the engine load set to full load, the intake valve opening timing InO is set to 0 deg to 40 deg after TDC of intake top dead center.
The simulation as shown in FIG. 7 was obtained by performing a simulation for measuring the changing state of the compression top dead center temperature while changing variously within the range of. From this data, the amount of retardation of the intake opening timing InO was set to 20 deg, and 2 hours after the compression top dead center.
When the intake valve 9 is opened at 0 deg, that is, when the intake valve opening timing InO is set at a time when the amount of gas blown back to the intake port 7 when the intake valve 9 is opened becomes substantially zero, the intake valve opening timing InO is set. Is set to the compression top dead center.
It was confirmed that the amount of change ΔT _TDC of the compression top dead center temperature was about 10 ° C. in the minus direction.

Further, in a four-stroke engine for a vehicle equipped with a phase-type variable valve timing device 13 for varying the opening / closing timing of the intake valve 9 while keeping the opening period of the intake valve 9 constant, the intake valve opening / closing timings InO and InC are set as described above. When the timing is set, the valve opening period of the intake valve 9 is increased by setting the retard amount of the intake valve closing timing InC to a predetermined value while maximally retarding the intake valve opening timing InO. As a result, it is possible to suppress knocking at the time of high load and high speed rotation of the engine as described above.

Therefore, when the engine that performs stratified combustion with the air-fuel ratio leaner than the stoichiometric air-fuel ratio is operated at a low load and at a low speed, the intake valve closing timing InC is advanced as compared with that at a high load and at a high speed. Even in the case where intake air suitable for stratified charge combustion is performed by suppressing the blowback of intake air due to the intake valve closing timing InC becoming too late, the intake valve opening timing InO is excessively advanced. It is possible to effectively prevent the adverse effect of this, that is, the occurrence of a situation in which a large amount of burned gas is blown back to the intake port when the intake valve 9 is opened and the combustion stability is impaired.

In the above embodiment, the turbocharger 5
0, a bypass passage 56 that bypasses the turbine 52 of the turbocharger 50, a wastegate valve 57 that opens and closes the bypass passage 56,
Intercooler 55 for cooling intake air supercharged by zero
When the retard control of the intake valve opening / closing timing is executed in the engine having the above, the intake air supercharged by the turbocharger 50 is supplied into the combustion chamber 5 while being cooled by the intercooler 55. Thus, the decrease in the amount of intake air due to the delay of the intake valve closing timing is compensated for according to the supercharging, thereby effectively reducing the decrease in engine output due to insufficient intake air charge. Can be prevented. In addition, by supplying the intake air cooled by the intercooler 55 into the combustion chamber 5 as described above, the rise in the compression top dead center temperature is suppressed, and the occurrence of knocking is effectively prevented, and the intake air amount is reduced. Sufficiently secured, it is possible to suppress a decrease in engine output.

Further, in the operating region on the high-speed rotation side, that is, in the operating region on the high-speed rotation side, from the intercept point (the calculated intercept point) at which the wastegate valve 57 is opened, the amount of exhaust gas driving the turbine 52 is large. In the case where the control of the opening / closing timing of the intake valve at the time of high load and high speed rotation is performed by the valve timing control means 42 in a state where the supercharging power is present in 50, conventionally, the wastegate valve 57 is opened by opening the wastegate valve 57. Since the supercharging is performed using the exhaust energy released to the atmosphere, the decrease in the amount of intake air due to the delay of the intake valve closing timing is ensured by the supercharging of the turbocharger 50. Can be supplemented. As a result, it is possible to reliably prevent the engine output from lowering due to insufficient charging of the intake air, and to further improve the engine output while suppressing the occurrence of knocking.

For example, if the geometric compression ratio of the engine is 1
A simulation was performed to measure the engine output Pe by varying the engine speed within the range of 1000 rpm to 6000 rpm in an engine set to a relatively high compression ratio of 0.2, as shown in FIG. Data was obtained. By executing the above-described control based on this data, as indicated by the broken line, the engine output P at an operating state of 5000 rpm which is the maximum output point of the engine is obtained.
It was confirmed that e could be improved by about 5%.

Note that, instead of the above embodiment, the valve timing control means 42 controls the opening and closing timing of the intake valve at the time of high load and high speed rotation in the operation range from the low speed rotation side to the high speed rotation side of the intercept point. In addition, the intake passage may be configured so that a dynamic effect of intake occurs near the intercept point. In the case of such a configuration, the amount of reduction of the intake air amount due to the delay of the intake valve closing timing on the low-speed rotation side of the intercept point where there is no surplus power by the turbocharger 50 is determined. ,
Since the pulsation effect of the intake air can make up for this, it is possible to effectively prevent a decrease in output due to insufficient filling of the intake air.

Further, as described above, the valve timing control means 42 controls the opening / closing timing of the intake valve at the time of high load and high speed rotation in the operation range from the low speed rotation side to the high speed rotation side of the intercept point. ,
There is an advantage that it is possible to prevent the occurrence of knocking in this region while preventing a decrease in engine output in a low-speed rotation region from the intercept point.

Further, as shown in the above embodiment, the exhaust valve closing timing Ex at the time of high load and high speed rotation of the engine is performed.
When C is set before the intake top dead center TDC,
When the intake valve 9 is opened, the burned gas remains in the combustion chamber 5 and an internal EGR effect is obtained. . Then, since the intake valve 9 is opened after the intake top dead center, the pressure in the combustion chamber 5 increases from the closing of the exhaust valve 10 to the intake top dead center, and the temperature in the combustion chamber 5 increases accordingly. After the heat is sufficiently dissipated during this period, the temperature drops with the pressure drop after the top dead center of the intake air. As a result, the burned gas in the combustion chamber 5 is cooled, and the combustion chamber 5 is cooled in the same manner as when the low-temperature EGR gas is introduced.
Since the effect of suppressing the temperature rise in the inside is obtained, there is an advantage that occurrence of knocking can be more effectively prevented.

[0059]

As described above, according to the engine of the present invention, when the engine is in the high-load and high-speed operation region, the intake valve opening timing is set to be after the intake top dead center and the intake valve is opened. The intake valve closing timing in the above-mentioned operating region is set to a timing later than the intake bottom dead center by a predetermined value or more, and the intake air amount is set at a point in time when the amount of gas blown back to the intake port becomes substantially zero by opening the intake port. Without increasing the valve opening period, it is possible to prevent a rise in the pre-compression temperature of the intake air due to a large amount of intake air flowing into the combustion chamber at a high speed when the intake valve is opened, and the geometric compression ratio is considerably large. Even at high engine temperatures, the effective compression ratio can be suppressed to an appropriate level to prevent temperature rise due to compression work inside the engine. The occurrence of knocking can be effectively suppressed, moreover in which the effect of such possible to prevent the stratified charge combustion resistance during low-load and low-speed rotation of the engine is impaired.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a four-stroke engine according to one embodiment of the present invention.

FIG. 2 is a diagram showing a cam lift curve for indicating opening / closing timing of an intake valve and an exhaust valve.

FIG. 3 is a partially enlarged view of a cam lift curve.

FIG. 4 is simulation data showing a change state of a flow velocity in an intake port.

FIG. 5 is simulation data showing a change state of a flow velocity peak in an intake port.

FIG. 6 is simulation data showing the degree of influence of each factor on a change in compression top dead center temperature.

FIG. 7 is simulation data showing a change state of a compression top dead center temperature.

FIG. 8 is simulation data showing a change state of an engine output.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine main body 5 Combustion chamber 9 Intake valve 10 Exhaust valve 13, 14 Variable valve timing device 42 Valve timing control means 50 Turbocharger 52 Turbine 55 Intercooler 56 Westgate passage 57 Westgate valve

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02B 29/04 F02B 29/04 Z 37/00 302 37/00 302A 37/18 F02D 23/00 K F02D 23 / 00 43/00 301R 43/00 301 301Z F02B 37/12 301A F-term (reference) 3G005 EA16 FA22 GA02 GB28 HA07 HA13 JA02 JA39 JA53 3G018 AA05 AB07 AB17 BA31 CA11 CA18 DA34 DA48 DA71 EA02 EA04 EA11 EA14 EA16 EA32 EA32 FA02 FA07 FA09 FA22 FA27 GA06 GA08 GA24 GA38 3G084 AA04 BA07 BA08 BA23 CA09 DA01 DA38 FA07 FA10 FA20 FA29 FA33 FA38 3G092 AA01 AA06 AA09 AA11 AA18 AB02 BA05 BA06 DA00 DA08 DA12 DC12 DF02 DF06 FA02 GA16 HA17 HA05 GA06 HD05Z HD09X HE01Z HE03Z HE08Z

Claims (5)

[Claims] 1. A four-stroke engine for a vehicle comprising a phase-type variable valve timing device that varies the opening / closing timing of an intake valve while keeping the opening period of the intake valve constant.
The intake valve opening timing in the operation region where the engine is under high load and high speed rotation is set to a point after the intake top dead center, at which time the amount of gas blown back to the intake port by opening the intake valve becomes substantially zero, and A four-stroke engine for an automobile, comprising: valve timing control means for setting the intake valve closing timing in a region to a timing later than a bottom dead center by a predetermined value or more. 2. A turbocharger, a bypass passage that bypasses a turbine of the turbocharger, a wastegate valve that opens and closes the bypass passage, and cools intake air supercharged by the turbocharger. 2. An intake cooler according to claim 1, further comprising an intercooler, wherein the valve timing control means controls the opening / closing timing of the intake valve in an operation range from a vicinity of an intercept point where the wastegate valve is opened to a high-speed rotation side. A four-stroke engine for an automobile according to the above. 3. The four-stroke engine for an automobile according to claim 2, wherein the control of the opening / closing timing of the intake valve by the valve timing control means is performed in an operation region on the high-speed rotation side of the intercept point. 4. The control of the opening / closing timing of the intake valve by the valve timing control means in an operation range from the low-speed rotation side to the high-speed rotation side of the intercept point, and the dynamic effect of intake near the intercept point is reduced. 3. An intake passage is formed so as to generate air.
A four-stroke engine for an automobile as described in the above. 5. The automotive vehicle according to claim 1, wherein the exhaust valve closing timing at the time of high load and high speed rotation of the engine is set before the intake top dead center.
Cycle engine.