JPH0763142A - Fuel injection pressure control device for direct injection engine - Google Patents

Abstract

PURPOSE:To maintain a fission length till starting atomization of infection fuel always in a desired length without unelessly increasing an injection pressure. CONSTITUTION:A recessed part 11 is formed in a top surface of a piston 3, a semispherical main combustion chamber is formed in an inner side of a partitioning part 12 protrusively provided from a bottom surface of the recessed part 11, and a circular annular outside combustion chamber 14 is formed in an outer side of the partitioning part 12. A spark plug 15 is arranged to appear in the main combustion chamber 13, and a fuel injection valve 16 is arranged to be directed to an inside surface 13a of the main combustion chamber 13. An injection pressure of a fuel injection valve 16 is changed in accordance with an engine speed, engine load, charging efficiency, etc., and a fission length of infection fuel (that is, length from injection hole of fuel injection valve 16 to position where atomization of injection fuel is started) is always obtained in a distance L or less from the injection hole of the fuel injection valve 16 to the inside surface 13a.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection pressure control device for a direct injection type engine in which fuel is directly injected from a fuel injection valve into a combustion chamber and ignition is performed by an ignition plug.

[0002]

2. Description of the Related Art Some of the Otto-type engines in which ignition is performed by a spark plug are those in which fuel is directly injected from a fuel injection valve into a combustion chamber (see, for example, Japanese Patent Application Laid-Open No. 1-203613). ). in this case,
Form a recess or combustion cavity on the top surface of the piston,
The injected fuel is directed to the combustion cavity, and a spark plug is arranged above the combustion cavity. In such a direct injection type spark ignition engine, by stratifying the fuel in the combustion cavity, the combustion stability can be sufficiently ensured while leaning the air-fuel ratio, and H
C can be reduced.

In the above-mentioned direct injection type spark ignition engine, it is desirable that the fuel be sufficiently atomized, that is, vaporized and atomized in the combustion cavity. That is, it is required to prevent non-atomized fuel from adhering to the inner wall surface of the combustion cavity. On the other hand, the fuel injected from the fuel injection valve is rapidly atomized when it reaches a certain distance, and the distance from the injection hole of the fuel injection valve to the position where rapid atomization is performed is generally the fragmentation length. Is called. It is known that the split length becomes shorter as the injection pressure from the fuel injection valve is increased. Japanese Unexamined Patent Publication No. 64-35011 discloses a diesel engine which is set to atomize the fuel before the fuel reaches the wall surface of the combustion chamber.

[0004]

In order to prevent fuel from adhering to the inner wall of the combustion cavity, the above-mentioned split length is
The distance may be set to be equal to or less than the distance between the injection hole of the fuel injection valve and the inner wall surface. However, since this split length changes under the influence of atmospheric pressure in the combustion chamber, etc., it is necessary to set the split length sufficiently short in order to always satisfy the above-mentioned requirements according to a wide operating condition. However, in this case, the driving loss for driving the pump for obtaining the injection pressure becomes large,
In addition, there is a problem in that the ambient air utilization rate is reduced, which is not preferable in securing the engine output.

Therefore, the object of the present invention is to control the fuel injection pressure of a direct injection type engine which can always optimize the split length of the injected fuel injected from the fuel injection valve without unnecessarily increasing the injection pressure. To provide a device.

[0006]

In order to achieve the above object, the present invention has the following configuration. That is, in a direct injection type engine in which fuel is directly injected from a fuel injection valve toward a predetermined combustion chamber wall and ignition is performed by a spark plug, an injection pressure adjusting means for adjusting a fuel injection pressure from the fuel injection valve is provided. Controlling the injection pressure adjusting means in accordance with the operating state of the engine so that the split length of the injected fuel is always less than or equal to the distance from the injection hole of the fuel injection valve to the predetermined combustion chamber wall. And an injection pressure control means for achieving the above. Preferred embodiments of the present invention based on the above configuration are as described in claims 2 and below in the claims.

[0007]

According to the present invention, the injection pressure is changed according to the operating state of the engine to make the split length of the injected fuel necessary and sufficient, so that the optimum fuel stratification can be achieved,
It is possible to prevent the injection pressure from being unnecessarily increased to prevent an increase in drive loss and a decrease in the air utilization rate.

With the structure as described in claim 2, the injection pressure can be optimally set corresponding to the change in the atmospheric pressure of the combustion chamber, and the effect obtained in claim 1 can be obtained.

With the configuration as set forth in claim 3, while obtaining the optimum fuel injection timing according to the engine speed and the engine load, the split length caused by the change of the fuel injection timing can be reduced. The change can be compensated to obtain the effect of claim 1.

With the structure as described in claim 4, the injection pressure can be changed in consideration of the filling efficiency that affects the split length, and the effect obtained in claim 1 can be obtained. In this case, with the configuration described in claim 5, the charging efficiency can be known by using general parameters such as intake air temperature and intake air pressure.

With the structure as described in claim 6, the injection pressure at the time of idling is set to the minimum injection pressure, which is preferable for reducing the drive loss. In this case, with the configuration as described in claim 7, when the exhaust gas temperature becomes low, the exhaust gas temperature is raised by throttling the intake air and the exhaust gas purifying catalyst is sufficiently activated, It can be compensated by increasing the injection pressure that the split length becomes longer by restricting the intake air.

With the structure as described in claim 8, even in the case of a supercharged engine, the injection pressure can be made appropriate and the effect obtained in claim 1 can be obtained.

With the structure as described in claim 9, during cold during which the atomization of fuel deteriorates and the split length becomes long, supercharging increases the air density and increases the ambient temperature. To increase fuel evaporation
It is possible to prevent the division length from becoming long. Then, in this case, the correction for reducing the injection pressure, which is performed due to the supercharging, is prohibited, and the situation in which the split length becomes too long due to this correction is prevented.

By adopting the structure as set forth in claim 10, the situation in which the air increase due to supercharging is delayed relative to the fuel increase due to acceleration, that is, the split length becomes long, is dealt with in response to supercharging. By prohibiting the correction of the decrease of the injection pressure and further increasing the injection pressure during acceleration, it is possible to surely prevent the decrease.

With the structure as set forth in claim 11, while stratifying the fuel in the main combustion chamber, the fuel leaking from the main combustion chamber is burned in the outer combustion chamber, that is, in the vicinity of the main combustion chamber as much as possible. Thus, the advantages of stratified combustion can be fully exhibited.

[0016]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In FIG. 1, 1 is a cylinder block, 2
Is a cylinder head, and 3 is a piston. A concave portion 11 is formed on the top surface of the piston 3, and an annular partition wall portion 12 projects from the bottom portion of the concave portion 11. As a result, a substantially hemispherical main combustion chamber 13 is formed inside the partition wall 12 inside the recess 11, and an annular outer combustion chamber 14 that surrounds the main combustion chamber 13 is formed outside the partition wall 12. To be done. The recess 11, that is, the main combustion chamber 13 and the outer combustion chamber 14 are slightly offset from the central axis of the piston 3 in the diameter direction of the piston 3.

A spark plug (ignition gap) 15 and a fuel injection valve 16 are attached to the cylinder head 2. The spark plug 15 is arranged at a position substantially above the center of the main combustion chamber 13. The fuel injection valve 16 is arranged near the outer peripheral edge of the piston 3, and its position is on the opposite side of the offset direction of the recess 11. That is, when considering the diametrical line of the piston 3, the recess 11 is offset to one end side thereof and the fuel injection valve 16 is arranged to the other end side thereof.

The fuel injection valve (injection hole thereof) is an inner side surface 13 of the inner side surface of the main combustion chamber 13 which is remote from the fuel injection valve 16.
It is directed toward a. Then, the fuel injection valve 16
The distance between (the injection hole) and the inner surface 13a on the far side is indicated by the symbol L. The top surface of the piston and the partition wall 1
2 is formed with a partial notch 3a or 12a for avoiding interference with the injected fuel so that the fuel from the fuel injection valve 16 reaches a desired position.

FIG. 2 shows an in-line four-cylinder engine E having a total of four combustion chamber structures as shown in FIG. 1 and its control system. That is, the engine E is configured so that intake air is distributed and supplied to each cylinder from the common intake passage 21 through the intake manifold 22, and the intake passage 21 includes the clutch 2
A supercharger 24, which is mechanically driven by the engine output shaft via 3, is provided.

Further, the intake passage 21 is provided with a bypass passage 25 for bypassing the supercharger 24. The bypass passage 25 is opened when the clutch 23 is disengaged and the supercharger 24 is stopped. The electromagnetic on-off valve 26 is connected. Further, the intake passage 21 includes the bypass passage 2
At the upstream side of 5, throttle valve 27 for throttled intake air
Is provided, the drive actuator of which is designated 28. It should be noted that this throttle valve performs a throttle action only when the exhaust gas temperature becomes lower than a predetermined temperature during idling, and is in a fully open state at other times. That is, in the embodiment, the throttle valve does not exist, and the load control (output control) of the engine is performed by controlling the fuel injection amount.

In FIG. 2, the fuel supply path to the fuel injection valve 16 is constructed as follows. First, the fuel (gasoline) pumped from the fuel tank 31 by the feed pump 32 is made to have a high pressure by the high-pressure fuel pump 33 and is supplied to the fuel pressure accumulator pipe 34. The injection valves 16 are individually connected.

The surplus fuel in the high pressure fuel pump 33 is
It is returned to the fuel tank 31 via the return passage 35, and a pressure adjusting valve 36 is connected to the return passage 35. That is, the fuel having a pressure higher than the set pressure of the pressure adjusting valve 36 is returned from the high pressure fuel pump 33 to the fuel tank 31. In addition, the fuel pressure accumulation pipe 34 is
The return passage 35 is connected to the high-pressure fuel pump 33 side of the return passage 35 via the flow passage 37. A variable electromagnetic pressure adjusting valve 38 is connected to the relief passage 37. By changing the valve opening pressure of the pressure adjusting valve 38, the pressure in the fuel pressure accumulating pipe 34, that is, the injection pressure from the fuel injection valve 16 is changed.

In FIG. 2, U is a control unit constructed by using a microcomputer. This control unit U
Controls the components 23, 26, 28, 38. For this control, signals from each sensor or switches S1 to S9 are input to the control unit U.
The sensor S1 detects the pressure in the fuel pressure accumulation pipe 34, that is, the injection pressure. The sensor S2 detects the engine speed. The sensor S3 detects an engine load such as an accelerator opening and a fuel injection amount corresponding to the opening. The sensor S4 detects the intake pressure. The sensor S5 detects the intake air temperature. Sensor S6
Is to detect acceleration, and can be configured to detect (calculate) the longitudinal acceleration acting on the vehicle body or the rate of change of the accelerator opening. The sensor S7 detects the exhaust temperature. The sensor S8 detects the cooling water temperature of the engine E. The switch S9 is an idle switch that is turned on when the accelerator pedal is not depressed.

The control unit U controls the injection pressure, which will be described later, and also performs the following control. First, clutch 2
3 is controlled to control whether or not supercharging is performed. The clutch 23 is connected and the supercharger 24 is operated.
It is considered that any one of the following conditions is satisfied. That is, when any one of the following conditions is satisfied: when the engine load is a high load above a predetermined load, acceleration is detected, or when the cooling water temperature of the engine E is below a predetermined temperature. Will be supercharged. The solenoid valve 26 is opened when the clutch 23 is disengaged and the supercharger 24 is stopped, and the solenoid valve 26 is closed when the supercharger 24 is operating (using the solenoid valve 26, When the boost pressure is released, the solenoid valve 2
6 may be opened.) Next, assuming that the engine is idle, when the exhaust temperature is a predetermined temperature or lower, for example, the exhaust gas purification catalyst is not sufficiently activated.
When the temperature is 0 ° C. or less, the throttle valve 27 is operated in the closing direction for a predetermined amount to throttle the intake air.

Next, the control of the injection pressure from the fuel injection valve 16 will be described. First, the control of the injection pressure is controlled so that the split length of the injected fuel (spray) from the fuel injection valve 16 is equal to or less than the distance L shown in FIG. And, in order to make this split length less than the distance L, it is satisfactory if the injection pressure is sufficiently increased (the split length becomes shorter as the injection pressure becomes larger), but it is unnecessary to shorten the split length unnecessarily. , The driving loss for driving the high-pressure fuel pump 33 becomes large, and the fuel splitting starts before the fuel reaches the main combustion chamber 13, which is not preferable. Therefore, the splitting length depends on various operating conditions of the engine. The injection pressure is controlled so as to be necessary and sufficient.

The division length can be expressed by the following equation (1) based on the experimental result. However, Lb = division length, D = hole diameter,
V = initial velocity of injection, Pa = atmospheric pressure, ρa = air density, ρ
e = fuel density, a = coefficient, b = coefficient (0.1 to 0.1
5), c = coefficient (0.5).

[0027]

[Equation 1]

Since the value obtained by squaring the injection initial velocity V is proportional to the pressure difference ΔP between the injection pressure and the atmospheric pressure, the following relational expression (2) is derived from the above expression (1). However, ρd = atmosphere density, α = coefficient (3 ± 0.5).

[0029]

[Equation 2]

As is clear from the above description, if the same split length is to be obtained, it is necessary to increase the injection pressure as the atmospheric pressure decreases. The following items are taken into consideration when setting the injection pressure. First, the larger the engine speed N, the more advanced (earlier) the request for the fuel injection start timing will be. However, because the advance angle reduces the atmospheric pressure, a large injection pressure is required. Become.
Secondly, as the engine load Q is larger, the request for the fuel injection start timing is advanced, so it is necessary to increase the injection pressure by this advance. However, the degree of increasing the injection pressure is smaller than the degree of increasing the injection pressure based on the engine speed if the amount of advance is the same. Thirdly, since the atmospheric pressure also changes depending on the filling efficiency, it is necessary to consider the filling efficiency.

Taking the above into consideration, in the embodiment,
The injection pressure PF is calculated by the following equation (3). However, P0 = minimum injection pressure, the map value is a stored value set with the engine speed N and engine load Q as parameters, and the filling efficiency correction value is expressed by the following equation (4).

PF = P0 × map value × filling efficiency correction value (3)

[0033]

[Equation 3]

However, in the equation (4), A = coefficient, Pi
= Intake pressure, Ta = intake temperature, α = coefficient (3 ± 0.5),
κ = specific heat ratio (1.39).

The pressure regulating valve 38 is feedback controlled while observing the output of the pressure sensor S1 so that the injection pressure is calculated on the basis of the expressions (3) and (4). However,
At the time of idling, when the engine cooling water temperature is lower than a predetermined temperature, and when accelerating, the following special injection pressure is set without depending on the expressions (3) and (4).

First, during idling, the injection pressure PF is basically set to the minimum injection pressure P0. However, when the exhaust gas temperature is lower than the activation temperature of the exhaust gas purification catalyst, the throttle valve 27 is operated to throttle the intake air by a predetermined amount, so that the exhaust gas temperature falls below a predetermined lower limit value (for example, 200 degrees C). Try not to. When the throttle valve 27 is operated,
Since the air density decreases, it is preferable to make the injection pressure larger than the minimum injection pressure P0 by performing the correction by the filling efficiency correction value in the equations (3) and (4) together. The coefficient A in the equation (4) for obtaining can be changed to the coefficient B only for the idle time so that the injection pressure larger than the injection pressure obtained by the coefficient A by a predetermined amount can be obtained.

Next, in the cold state, since the temperature is low, atomization of the fuel is deteriorated, and the split length is increased. Therefore, it is possible to prevent the division length from being lengthened by performing supercharging to increase the air density and the intake air temperature, and further to advance the fuel injection timing to lengthen the evaporation time. However, if the correction based on the filling efficiency correction value in the equations (3) and (4) is performed as it is, the injection pressure becomes small because the intake pressure becomes large due to supercharging, so the intake pressure Correction (supercharging correction) is prohibited.
The prohibition of the correction by the intake pressure can be performed by prohibiting the correction itself by the filling efficiency correction value shown in the equations (3) and (4) (the filling efficiency correction value is fixedly set to "1"). Same as the above), the parameter to obtain the filling efficiency correction value.
Instead of using the intake pressure detected by the sensor S4, a certain constant value for cold may be used as the magnitude of the intake pressure.

Further, at the time of acceleration, the fuel amount is increased and supercharging is performed. However, since the increase in the air amount due to the supercharging is delayed with respect to the increase in the fuel amount, the atmospheric pressure is reduced and the split length is increased. Will end up. Therefore, at the time of acceleration, the correction based on the filling efficiency correction value shown in the equations (3) and (4) is prohibited, and the acceleration correction value (1 + β × G) is used instead as shown in the following equation (5). To be That is, PF = P0 × map value × (1 + β × G) (5) is set. In addition, β is a coefficient, and G is acceleration (for example, accelerator opening change rate).

The control contents described above are applied to the flow chart of FIG.
In FIG. 3, R (step-
The same applies hereinafter) 2 is the process of determining the map value in the formulas (3) and (4), and R11 is the process of determining the filling efficiency correction value in the formula (3). Further, R4 is a process for setting the minimum injection pressure P0 for idle, and R6 is a process when the exhaust temperature is low. Further, the injection pressure setting for cold time is R10, and the injection pressure setting for acceleration is R8.

[Brief description of drawings]

FIG. 1 is a side sectional view showing an example of a combustion chamber structure to which the present invention is applied.

FIG. 2 is an overall control system diagram for an engine having the combustion chamber structure shown in FIG.

FIG. 3 is a flow chart showing control contents in the present invention.
To.

[Explanation of symbols]

 1: Cylinder Block 2: Cylinder Head 3: Piston 11: Recess 12: Partition 13: Main Combustion Chamber 14: Outer Combustion Chamber 15: Spark Plug 16: Fuel Injection Valve 33: High Pressure Fuel Pump 34: Fuel Accumulation Pipe 37: Lily -Flow passage 38: Pressure regulating valve U: Control unit S1: Pressure sensor S2: Engine speed sensor S3: Engine load sensor S4: Intake pressure sensor S5: Intake temperature sensor S6: Acceleration sensor S7: Exhaust temperature sensor S8: Water temperature sensor S9: Idle switch

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication location F02D 41/04 345 C 8011-3G 41/08 360 8011-3G 41/32 A 8011-3G 45 / 00 301 EF02M 37/00 QC 61/14 310 A

Claims (11)

[Claims] 1. A direct injection engine in which fuel is directly injected from a fuel injection valve toward a predetermined combustion chamber wall and is ignited by an ignition plug. An injection pressure for adjusting a fuel injection pressure from the fuel injection valve. The injection pressure adjusting means is controlled in accordance with the adjusting means and the operating state of the engine so that the split length of the injected fuel is always less than or equal to the distance from the injection hole of the fuel injection valve to the predetermined combustion chamber wall. A fuel injection pressure control device for a direct injection type engine, comprising: 2. The injection pressure according to claim 1, wherein the lower the atmospheric pressure in the combustion chamber, the higher the injection pressure. 3. The fuel injection start timing is set to advance with an increase in at least one of the engine speed and the engine load, and the injection pressure is increased as the advance is increased. Things. 4. The injection pressure according to claim 1, wherein the injection pressure is changed according to the filling efficiency into the combustion chamber. 5. The device according to claim 4, wherein at least one of intake air temperature and intake air pressure is used as a parameter indicating the charging efficiency. 6. The injection pressure according to claim 1, wherein the injection pressure is set to a minimum injection pressure during idling. 7. The throttle device according to claim 6, further comprising throttle means for throttling the intake air when the exhaust gas temperature becomes low during idling, and when the throttle means is operated, the injection pressure is made higher than the minimum injection pressure. thing. 8. The turbocharger according to claim 1, further comprising a supercharger for supercharging intake air, and a basic correcting means for reducing the injection pressure when the supercharging pressure is large compared to when the supercharging pressure is small. 9. The system according to claim 8, wherein when the engine is cold, the supercharger is operated to perform supercharging and the correction by the basic correcting means is prohibited. 10. The acceleration correction according to claim 8, wherein at the time of acceleration, the supercharger is operated to perform supercharging, the correction by the basic correction means is prohibited, and the injection pressure increases as the acceleration increases. What is done. 11. The method according to any one of claims 1 to 10.
In the paragraph (1), a recess is formed on the top surface of the piston, and a partition wall projects from the bottom wall of the recess, the inside of the partition wall is the main combustion chamber, and the outside of the partition wall is the main combustion chamber. An outer combustion chamber having an annular shape surrounding the inner combustion chamber, and the fuel injected from the fuel injection valve is directed toward the inner surface of the main combustion chamber.