JP2000073815A - Fuel injection control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure a step-down property of a common rail with a simple structure. SOLUTION: From a common rail 3 that stores pressurized fuel, fuel is supplied to a fuel injection valve 1 that directly injects fuel to each cylinder of an engine 10. The fuel injection valve 1 executes a secondary fuel injection in expansion stroke or exhaust stroke of the cylinders as the need arises, other than the regular fuel injection. When it is necessary that common rail pressure should be dropped in fuel cut operation, an electronic control unit(ECU) 20 makes the fuel injection valve 1 execute invalid injection operation that is not accompanied by an actual fuel injection. Fuel is returned to a fuel tank 7 according to the invalid injection operation, so that the common rail pressure is dropped. When the secondary fuel injection is executed, the invalid fuel operation is stopped at a predetermined period before the secondary fuel injection is started so as to prevent interference between the invalid injection operation and the secondary fuel injection. Accordingly, step-down of the common rail by the invalid injection operation can be implemented, in an engine that executes the secondary fuel injection.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a fuel injection device for an internal combustion engine.

[0002]

2. Description of the Related Art Fuel is supplied from a high-pressure fuel pump to a common accumulator (common rail), and a fuel injection valve for each cylinder is connected to the accumulator to supply high-pressure fuel stored in the accumulator to each cylinder of the internal combustion engine. 2. Description of the Related Art There is known a so-called pressure accumulation type (common rail type) fuel injection device that injects fuel into a fuel cell.

In the common rail type fuel injection device, the injection rate of the fuel injection valve is controlled by the fuel pressure in the common rail, and the fuel injection amount is controlled by both the fuel pressure in the common rail and the valve opening (fuel injection) time of the fuel injection valve. Is done. Therefore, in the accumulator type fuel injection device, it is necessary to control the injection rate (common rail internal pressure) according to the engine operating state. In particular, in a diesel engine or the like that performs high-pressure fuel injection, the common rail pressure may vary over a wide range according to the operating state of the engine, and may vary, for example, from about 10 MPa to about 150 MPa. For this reason, in the common rail type fuel injection device, it is necessary to control the pressure in the common rail in a wide pressure range with good responsiveness according to the engine operating state.

Further, a common rail type fuel injection device is provided.
Engine, the expansion stroke or exhaust after main fuel injection in each cylinder
By performing secondary injection during the stroke, the operating air-fuel ratio of the engine
The exhaust air-fuel ratio without affecting the engine (rich)
It is possible to do. The exhaust air-fuel ratio is
NO during exhaust_XTo reduce exhaust air-fuel ratio.
NO absorbed when_XRelease and purify
NO_XAdsorb and reduce hydrocarbons in storage reduction catalysts and exhaust
NO in exhaust even when the air-fuel ratio is lean_XAdsorbed
Selective reduction catalyst that can be selectively reduced and purified using hydrocarbons
NO such as _XPurification catalysts are known. Such NO_X
Purification catalysts such as diesel engines and lean air-fuel ratio operation
When applying to a gasoline engine that performs_X
By supplying exhaust gas with a rich air-fuel ratio to the purification catalyst, NO_XRelease
Out, reduction and purification, or adsorption of hydrocarbons to catalyst
It is necessary. In such a case, the engine operating air-fuel ratio
(Combustion air-fuel ratio in engine combustion chamber)
When switching to the air-fuel ratio, the engine output
The torque fluctuates or the in-cylinder combustion pressure becomes excessive.
Problems arise.

In an engine equipped with a common rail type fuel injection device, by performing secondary fuel injection in such a case, only the exhaust air-fuel ratio is switched rich without changing the engine operating air-fuel ratio or the in-cylinder combustion pressure. It becomes possible. That is, the fuel injected during the expansion stroke and the exhaust stroke of each cylinder is vaporized without contributing to combustion in the cylinder, and is discharged from the cylinder together with the exhaust. Therefore, the exhaust air-fuel ratio can be changed to the rich air-fuel ratio without affecting the operating air-fuel ratio and the combustion pressure in the cylinder.

[0006]

As described above, it is necessary to control the common rail pressure in a wide range with good responsiveness in accordance with the operating state of the engine. Here, it is relatively easy to increase the pressure of the common rail by increasing the amount of fuel pumped from the high-pressure fuel pump, but in order to reduce the common rail pressure, the fuel in the common rail must be removed from the common rail. Must be discharged. In this case, when the fuel is being injected into the engine, the fuel in the common rail is injected into the cylinder from the fuel injection valve, so that the common rail pressure can be reduced relatively quickly. However, for example, when fuel injection is stopped due to fuel cut or the like at the time of engine braking, it is necessary to provide another means in order to ensure the pressure drop of the common rail. Therefore, in order to ensure the pressure drop of the common rail, an electromagnetic pressure relief valve (relief valve) for discharging the fuel in the common rail to the fuel tank has conventionally been provided. However, especially in a diesel engine or the like that performs high-pressure fuel injection, the common rail pressure may be extremely high, so that the rated pressure of the electromagnetic pressure relief valve to be used needs to be increased, so that the cost of the electromagnetic pressure relief valve increases.

On the other hand, some fuel injection valves open the fuel injection valve by applying fuel oil pressure to both sides of the valve body and reducing the oil pressure on one side of the valve body. In this type of fuel injection valve, a small amount of fuel oil is returned to the fuel tank along with the fuel injection valve opening operation. However, when the valve opening time of the fuel injection valve is very short, the valve body does not actually start moving even if the hydraulic pressure acting on the valve body is reduced, and actually the No fuel injection occurs. That is, by performing the fuel injection valve opening operation for a short time, it becomes possible to return the fuel oil from the fuel injection valve to the fuel tank without actually injecting the fuel into the cylinder. In this specification, such a fuel injection operation that does not involve actual fuel injection is referred to as an invalid injection operation of the fuel injection valve.

By utilizing this invalid injection, it becomes possible to discharge the fuel in the common rail to the fuel tank through the fuel injection valve even during fuel cut operation such as engine braking. In this case, since the amount of fuel discharged from the common rail by one invalid injection is small, it is necessary to repeat the invalid injection from each fuel injection valve at short time intervals in order to secure the pressure drop of the common rail.

[0009] However, in the engine causing secondary fuel injection for of the NO _X purification catalyst as described above, there is a case where the performing the invalid injection operation of the fuel injection valve problems for common rail buck occurs. That is, since the secondary fuel injection is performed according to the request of the NO _X purification catalyst, it may be necessary to execute the secondary fuel injection even during the fuel cut operation of the engine. Also, since the secondary fuel injection is performed during the expansion or exhaust stroke of each cylinder,
This is performed in synchronization with the engine crank rotation angle. On the other hand, in order to ensure sufficient common rail pressure drop, the invalid injection operation needs to be performed at predetermined time intervals (as short as possible) without synchronizing with the crank rotation angle. in this case,
Since both the secondary fuel injection and the invalid injection operation are performed by the same fuel injection valve, if the secondary fuel injection and the invalid injection operation for reducing the common rail pressure are performed in parallel, the secondary fuel injection and the invalid injection operation are performed on the fuel injection valve. In some cases, the next fuel injection command and the invalid injection operation command overlap or are output in close proximity, and the operation of the fuel injection valve may be incomplete. For this reason, the engine that performs the secondary fuel injection cannot perform the step-down control of the common rail by the invalid injection operation, and thus requires the use of a high-cost electromagnetic pressure relief valve.

The present invention solves this problem and eliminates the use of a high-cost electromagnetic pressure relief valve by enabling the common rail pressure to be reduced by an invalid injection operation without obstructing the operation of the fuel injection valve even when performing secondary fuel injection. It is an object of the present invention to provide a fuel injection control device capable of performing the above.

[0011]

According to the first aspect of the present invention, an accumulator for storing pressurized fuel, a fuel injector for injecting fuel from the accumulator into an internal combustion engine, and the fuel injector A fuel injection control means for controlling the fuel injection to the engine by injecting the fuel into the engine. Performs a secondary fuel injection for injecting fuel into the engine, and further reduces the pressure in the accumulator if necessary, at a predetermined time interval, an invalid injection operation without actual fuel injection of the fuel injection valve. Performing both the secondary fuel injection and the invalid injection operation, the fuel injection control device characterized by stopping the invalid injection operation for a predetermined period before the secondary fuel injection execution Provided.

That is, according to the first aspect of the present invention, when both the secondary fuel injection and the invalid injection operation for stepping down the common rail are executed, the invalid injection operation is performed for a predetermined period before the execution of the secondary fuel injection. I'm trying to stop. Since both the invalid injection operation and the secondary fuel injection discharge fuel from the common rail, even if the invalid injection operation is stopped at the time of secondary fuel injection of the fuel injection valve, the pressure drop of the common rail can be ensured. On the other hand, the secondary fuel injection is to carry out for such NO _X purification catalyst, it is impossible to stop the secondary fuel injection for the invalid injection operation. In the present invention, when the invalid injection operation of the fuel injection valve and the secondary fuel injection interfere,
By stopping the invalid injection operation during the period that causes interference,
The effect on the secondary fuel injection is prevented without impairing the pressure drop of the common rail. Note that the period during which the invalid injection operation is stopped is set to, for example, a minimum time required for preparing for the secondary fuel injection (for example, a power charging time for opening the fuel injection valve).

According to the second aspect of the present invention, the fuel injection control means calculates a time from a predetermined reference time to the start of the secondary fuel injection, and an invalid injection operation that can be executed within the time. 2. The method of claim 1, further comprising: setting the number of times, stopping the invalid injection operation when the set number of invalid injection operations is performed, and canceling the invalid injection operation stop after the end of the secondary fuel injection.
Is provided.

That is, according to the second aspect of the present invention, the time from the reference time to the time when the secondary fuel injection is to be started is calculated, and the invalid injection operation is performed based on the number of invalid injection operations that can be executed in this time. Control the stop. Therefore, for example, even when the secondary fuel injection timing is specified by the crank rotation angle and the invalid injection operation is specified by the operation execution interval, the interference between the secondary fuel injection and the invalid injection operation is reliably prevented. In addition, since the stop of the invalid injection operation is released after the end of the secondary fuel injection, the invalid injection operation is restarted as necessary, and the pressure drop of the common rail is reliably maintained.

[0015]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram showing a schematic configuration of an embodiment in a case where the present invention is applied to a common rail type fuel injection device for an automobile diesel engine. In FIG. 1, reference numeral 1 denotes a fuel injection valve for directly injecting fuel into each cylinder of an internal combustion engine 10 (a four-cylinder diesel engine is used in this embodiment), and 3 denotes a common fuel injection valve to which each fuel injection valve 1 is connected. Shows the common rail (accumulator). The common rail 3 has a function of storing pressurized fuel supplied from a high-pressure fuel pump 5 described later and distributing it to each fuel injection valve 1.

In FIG. 1, reference numeral 7 denotes a fuel tank for storing fuel (light oil in this embodiment) of the engine 10, and reference numeral 9 denotes a low-pressure feed pump for supplying fuel to a high-pressure fuel pump. During operation of the engine, the fuel in the tank 7
The pressure is increased to a constant pressure by the feed pump 9 and supplied to the high-pressure fuel injection pump 5. The fuel discharged from the high-pressure fuel pump 5 is supplied to the common rail 3 through the check valve 15 and the high-pressure pipe 17, and is injected from the common rail 3 into each cylinder of the internal combustion engine through each fuel injection valve 1. You.

In FIG. 1, reference numeral 19 denotes a return fuel pipe for returning the return fuel from each fuel injection valve 1 to the fuel tank 7. Return fuel from the fuel injection valve will be described later. In FIG. 1, an electronic control unit (ECU) 20 controls the engine. EC
U20 is a read only memory (ROM), a random access memory (RAM), a microprocessor (CP
U), it is configured as a microcomputer having a known configuration in which input / output ports are connected by a bidirectional bus. ECU
Reference numeral 20 denotes a fuel pressure control that controls the discharge amount control mechanism 5a of the high-pressure fuel pump 5 to control the fuel oil pressure in the common rail 3 according to the engine load, the number of revolutions, and the like, as will be described later. The rate is adjusted according to the engine load, the number of revolutions, and the like, and the fuel injection control for controlling the amount of fuel injected into the cylinder by controlling the valve opening time of the fuel injection valve 1 is performed.

In this embodiment, as described later, E
The CU 20 performs an invalid injection operation of each fuel injection valve 1 when reducing the pressure in the common rail. Further, in the present embodiment is provided NO _X purification catalyst of the NO _X occluding and reducing catalyst and the like (not shown) in the exhaust passage of the engine 10, ECU
Reference numeral 20 periodically performs secondary fuel injection to supply exhaust gas having a rich air-fuel ratio to the NO _X purification catalyst. The invalid injection operation and the secondary fuel injection will be described later.

For the above control, a voltage signal corresponding to the fuel pressure in the common rail 3 is supplied to the input port of the ECU 20 from the fuel pressure sensor 31 provided on the common rail 3.
In addition to the signal input via the converter 34, a signal corresponding to the amount of depression of the accelerator pedal (accelerator opening) by the driver from an accelerator opening sensor 35 provided on an engine accelerator pedal (not shown) is an AD converter. 34 has been entered. Further, the input port of the ECU 20 has a crank angle sensor 3 provided near the crankshaft (not shown) of the engine.
7, a reference pulse signal generated when the crankshaft reaches a reference rotational position (for example, compression top dead center of the first cylinder) and a crank rotation angle (for example, every 15 degrees of the crank rotation angle) are generated. Two signals, a rotation pulse signal, are input. The ECU 20 calculates the engine speed (rotation speed) from the interval between the input rotation pulse signals and the rotation phase of the crankshaft from the number of rotation pulse signals after the input of the reference pulse signal.

An output port of the ECU 20 is connected to the fuel injection valve 1 via a fuel injection circuit 40.
Of the high-pressure fuel pump 5 via a drive circuit 41.
Is controlled. In the present embodiment, the high-pressure fuel injection pump 5 is an appropriate type of high-pressure pump such as a piston pump or an inner cam pump, and is driven by the crankshaft of the engine 10. The high-pressure fuel pump 5 has a flow control mechanism 5a for controlling the pump discharge amount. The flow control mechanism 5a controls the amount of fuel flowing into the pump by controlling, for example, the suction amount of the high-pressure fuel pump 5, or controls the pump discharge amount by returning a part of the pump discharge to the fuel tank. Any of these can be used.

In the present embodiment, the ECU 20 sets the target common rail fuel pressure based on a numerical map stored in the ROM in advance according to the engine load (accelerator opening) and the number of revolutions, and sets the common rail fuel pressure detected by the fuel pressure sensor 31. The discharge amount of the pump 5 is controlled so that the fuel pressure becomes the set target common rail fuel pressure. Also, ECU
Reference numeral 20 controls the valve opening time (fuel injection time) of the fuel injection valve 1 based on a numerical map stored in the ROM in advance according to the engine load and the number of revolutions.

That is, in this embodiment, the common rail 3
By changing the fuel pressure according to the engine operating conditions, the injection rate of the fuel injector 1 is adjusted according to the operating conditions,
By changing the fuel pressure and the fuel injection time, the fuel injection amount is adjusted according to the operating conditions. For this reason, in the common rail type fuel injection device as in the present embodiment, the fuel pressure in the common rail is in a very wide range according to the operating conditions (load, rotation speed) of the engine (for example, about 10 MPa to 150 MPa in the present embodiment). (In the range up to).

Next, the secondary fuel injection from the fuel injection valve 1 will be described. As described above, in an exhaust passage of the engine 10 in the present embodiment is provided NO _X purification catalyst (not shown), a rich air-fuel ratio rich in unburned hydrocarbons in the NO _X purification catalyst at regular intervals It is necessary to supply exhaust gas. However, in this embodiment, a diesel engine is used as the engine 10. Since a diesel engine is operated at a lean air-fuel ratio with an extremely high excess air ratio, it is necessary to burn a large amount of fuel in the cylinder in order to generate exhaust gas with a rich air-fuel ratio by combustion in the cylinder. For this reason, when attempting to generate exhaust with a rich air-fuel ratio by in-cylinder combustion, combustion of a large amount of fuel greatly increases the in-cylinder combustion pressure and reduces the durability of the engine, or the engine output torque increases sharply, resulting in sudden increase in engine output torque It may cause trouble. Therefore, in the present embodiment, the air-fuel ratio of the exhaust gas discharged from the cylinder is made rich by performing secondary fuel injection into the cylinder during expansion or exhaust stroke after combustion by normal fuel injection occurs in each cylinder. The air-fuel ratio is set. Fuel injected into the cylinder during the expansion or exhaust stroke vaporizes without burning, and generates low molecular weight hydrocarbons due to high pressure and high temperature in the cylinder. Therefore, when secondary fuel injection is performed, the exhaust gas discharged from the cylinder contains a large amount of hydrocarbons. Further, since the fuel injected by the secondary fuel injection does not contribute to the combustion in the cylinder, even if the secondary fuel injection of an amount of fuel sufficient to make the exhaust air-fuel ratio a rich air-fuel ratio is performed, the in-cylinder combustion pressure and the The engine output torque does not increase. For this reason, it is possible to supply exhaust gas with a rich air-fuel ratio containing a large amount of unburned hydrocarbons to the NO _X purification catalyst without affecting the operation of the engine 10 by the secondary fuel injection.

Next, the invalid injection operation of the fuel injection valve will be described. Since the fuel injection valve 1 of the present embodiment performs the valve opening operation of the fuel injection valve using the pressure of the fuel oil, a certain amount of the fuel oil determined from the fuel injection condition is returned to the fuel tank with the fuel injection operation. . The return pipe 19 in FIG. 1 is for returning the return fuel accompanying the fuel injection valve opening operation to the fuel tank 7. The return fuel will be described in more detail. In the fuel injection valve of the present embodiment, since the fuel pressure is high, it is difficult to hold the fuel injection valve closed only by the force of a spring or the like. Therefore, when the fuel injection valve is closed, the force applied to the valve body by the fuel oil pressure is balanced by applying the fuel pressure oil force to both the lower part (injection hole side) and the upper part of the valve body, and the spring force is used. The valve body is pressed against the valve seat. On the other hand, at the time of fuel injection, the pressure acting on the upper part of the valve body is reduced by allowing the fuel oil on the upper part of the valve body to escape to the return pipe via the solenoid valve and the measuring orifice. Thus, the valve body is pushed up against the spring by the fuel oil pressure acting on the lower part of the valve body, and the injection hole is opened, so that fuel injection is performed. For this reason, fuel returns from the fuel injection valve to the fuel tank during the fuel injection valve opening operation. The return fuel is generated by allowing fuel oil, which exerts pressure on the upper part of the valve body to operate the valve body of the fuel injection valve, to escape to the return fuel pipe 19 through the orifice. However, usually, a certain amount of time is required from when the solenoid valve is opened and the fuel oil above the valve body begins to escape to when the valve body actually starts moving.
If the fuel oil is simply released from the upper portion of the valve body for a short time, the valve body does not start moving and the fuel injection from the fuel injection valve does not occur. However, also in this case, oil is released from the upper portion of the valve body through the orifice, that is, return fuel is generated. Therefore, in the present embodiment, the solenoid valve in the fuel oil release passage from the upper part of the valve body is set to a time significantly shorter than the solenoid valve opening time during normal fuel injection operation (for example, a time of 600 × 10 ⁻⁶ seconds or less).
Only the return fuel is produced without actual fuel injection. In this specification, this valve opening operation without actual fuel injection is referred to as an invalid injection operation.

As described above, by performing the invalid injection operation, a small amount of fuel can be discharged from the common rail 3 to the fuel tank 7 through the fuel injection valve 1. As described above, during the normal fuel injection (fuel injection for burning in the cylinder), a relatively large amount of fuel is supplied from the common rail into the cylinder via the fuel injection valve 1, so that the common rail 3 The pressure can be changed relatively easily by controlling the discharge amount of the high-pressure fuel pump 5. However, while fuel cut is performed by engine braking or the like, normal fuel injection is stopped. Therefore, even if the discharge amount of the high-pressure fuel pump 5 is controlled to zero, the pressure of fuel already in the common rail 3 is reduced. Cannot be reduced. On the other hand, since the common rail 3 pressure needs to be controlled with good responsiveness according to the engine operating state, it may be necessary to rapidly reduce the common rail 3 pressure even during fuel cut operation. Conventionally, an electromagnetic pressure relief valve for discharging the fuel in the common rail 3 to the fuel tank 7 is provided in preparation for such a case, and when it is necessary to reduce the common rail pressure during the fuel cut operation, the electromagnetic pressure relief valve is opened. It was necessary to return the fuel in the common rail 3 to the fuel tank 7. However, since the maximum pressure of the fuel in the common rail 3 is extremely high, it is necessary to use an electromagnetic pressure relief valve having a high rated pressure, which causes a problem that the cost of the electromagnetic pressure relief valve body is increased.

As described above, in this embodiment, the fuel can be discharged from the common rail 3 to the fuel tank 7 by performing the invalid injection operation of the fuel injection valve. Therefore, in this embodiment, the common rail pressure drop control is performed by performing an invalid injection operation of the fuel injection valve during the fuel cut operation without providing an expensive electromagnetic pressure relief valve on the common rail. Since the amount of return fuel generated by the invalid injection operation is relatively small, the necessary pressure reduction operation is performed by repeating the invalid injection operation of each fuel injection valve at short time intervals during the common rail pressure reduction control. Further, the invalid injection operation is not limited to the fuel cut operation, and may be performed as needed during an operation in which normal fuel injection is performed, so that the responsiveness of the pressure control of the common rail 3 may be improved.

By the way, there is a case where the secondary fuel injection at the request of the NO _X purification catalyst also invalid injection operation even during implementation for the common rail buck is executed. Further, as described above, the secondary fuel injection is executed in synchronization with the crank rotation angle of the engine 10, whereas the invalid injection operation is repeated at regular intervals. For this reason, if the secondary fuel injection is performed during the common rail step-down operation by the invalid injection operation,
In some cases, the invalid injection operation command and the secondary fuel injection command for the fuel injection valve overlap or are issued in close proximity. Since the fuel injection valve needs time to charge the power of the solenoid of the solenoid valve to perform the fuel injection operation, after performing the fuel injection operation, the fuel injection valve performs the next fuel injection operation until the charging period elapses. It is not possible. Therefore, when two fuel injection operation commands are issued in close proximity, the solenoid valve may not be able to operate completely in response to the subsequent fuel injection operation command, and the invalid injection operation or the secondary fuel injection may be incomplete. Problem arises.

In the present embodiment, when the invalid injection operation command for the common rail step-down operation and the secondary fuel injection command are close to each other and cause the above-mentioned interference, the secondary fuel injection is executed with priority. The invalid injection operation is prohibited until the next fuel injection ends. This is because the fuel is discharged from the common rail also by the secondary fuel injection, so the pressure of the common rail is also reduced by the secondary fuel injection,
This is because the secondary fuel injection cannot be substituted for the invalid injection operation.

According to this embodiment, when the invalid injection operation and the secondary fuel injection interfere with each other, the invalid injection operation is prohibited. The operation makes it possible to perform the step-down control of the common rail, so that even in an engine that performs secondary fuel injection, it is possible to omit the electromagnetic relief valve of the common rail.

FIG. 2 is a timing chart for explaining the invalid injection operation control of this embodiment. In the present embodiment, the time (T in FIG. 2) from this reference point to the start timing of the secondary fuel injection is calculated based on the time point before the secondary fuel injection execution timing by a predetermined crank rotation angle. Then, the number nj of invalid injection operations that can be executed within this time is set to the invalid injection time interval tin.
t (FIG. 2), time t required to charge the solenoid power
_ch and safety margins t _a and t _s . Then, the invalid injection operation is performed every time tint for the calculated number of times, and then the invalid injection operation is stopped.

First, the calculation of the time T until the next secondary fuel injection is performed will be described. The calculation timing of the time T (reference timing) and the secondary fuel injection start timing are specified by the numbers of the rotation pulse signals input from the crank angle sensor 37, respectively. As described above, in the present embodiment, the ECU 20
, A rotation pulse signal is input from the rotation angle sensor every 10 ° of the crank rotation angle, and a reference pulse signal is input each time the crankshaft reaches a reference position (for example, the top dead center of the compression of the first cylinder).
The ECU 20 counts the rotation pulse signal after the input of the reference pulse signal, and sets the time when the ith pulse signal is input after the input of the reference pulse signal as a reference point for calculating the time T, and inputs the (i + k) th pulse signal. Then, the secondary fuel injection is started. Also, for example, the ECU 2
A value of 0 stores the pulse interval after the input of the reference pulse signal for one rotation of the engine, and is updated every time a rotation pulse is input. (For example, the time interval between the n-th pulse signal and the (n + 1) -th pulse signal is represented by t _n (ms), and a set of 36 time interval data for one rotation from t ₁ to t ₃₆ is always stored and updated. And the time T from the reference point to the secondary fuel injection start timing.
(Ms) is T = Σ (n = i ＝ (i + k−1)) t _n +
It is calculated as t _m.

Here, Σ (n = i〜 (i + k−1)) t
_nIs the ith of the currently stored time interval data
Data (t_i) To (i + k-1) th data (t
_{(i + k -1)}). Also, t_mIs (i
+ K-1) The second fuel injection actually starts after the pulse input
It is time to start. That is, the time T is
Pulse interval t obtained during rotation of_iTo t
_{(i + k-1)}Is calculated (estimated) by integrating
You. In addition, for the time of one revolution of the crankshaft (36 pieces) at all times
Instead of memorizing the interval
In addition, the time interval for one cycle of cylinder stroke (18 pieces) is stored.
And calculate T from the corresponding time interval data.
May be. In this case, the rotation speed before one cylinder cycle
Is calculated on the basis of.

[0033] In addition, the number nj of executable invalid injection operation until the secondary fuel injection start timing, nj = ((T-t a -
t _ch −t _s ) / tint) +1). Here, t _a is the time from the reference time to the time when the first invalid injection operation is actually performed, and t _ch is the time required for charging the solenoid of the fuel injector for the secondary fuel injection (several ms).
Degree), t _s is the time for rotation error correction. While the reference time is determined by the crank rotation angle, the invalid injection operation is performed by a time interruption routine executed by the ECU. Time t _a represents the time from when the i-th pulse is input to when the time interrupt routine is first executed until the invalid injection operation is performed. Further, the time T calculated as described above is based on the data at the time of the previous crank rotation, and becomes a value including an error if the crankshaft rotation speed has changed from the previous time. t _s is a time for correcting this error. Note that t _a and t _s are set in advance as appropriate values including a certain margin for safety. Also, invalid injection operation execution interval tint is set to as short as possible distance in the power charge time t _ch greater range.

The ECU 20 executes the invalid injection operation the number of times calculated as described above by an interrupt routine for a predetermined time, which will be described separately, and then temporarily suspends the invalid injection operation. When the secondary fuel injection ends in a routine (not shown) separately executed by the ECU 20, the stop of the invalid injection operation is released and the invalid injection operation is restarted if necessary. Thereby, the invalid injection operation is not performed in the portion indicated by the oblique lines in FIG. 2, so that the secondary fuel injection is prevented from being affected by the invalid injection operation.

Next, the control of the invalid injection will be described in detail with reference to FIGS. FIG. 3 is a flowchart showing a time T from the reference time to the start of the next secondary fuel injection and an operation for calculating the number of invalid injection operations nj that can be executed within that time. This operation is performed by the ECU 20 using the crank rotation angle 1
It is executed every 5 ° (each time a rotation pulse signal is input from the crank angle sensor 37).

When the operation is started in FIG. 3, in step 301, the pulse number p input this time is determined.
Further, the time interval between the previously input pulse p-1 and the current pulse p is stored as time interval data tp _-1 . Then, in step 303, it is determined whether or not it is the current timing of calculating the number of invalid injection operations nj, that is, whether or not the input pulse number p matches i. If p = i, that is, if it is time to calculate nj, the process next proceeds to step 305, and it is determined whether secondary fuel injection is scheduled this time. Whether or not the secondary fuel injection is scheduled this time is determined by whether or not the secondary fuel injection amount is set in the fuel injection circuit 40 in a secondary fuel injection amount calculation routine that is separately executed by the ECU 20.

If the secondary fuel injection is scheduled this time, the routine proceeds to step 307, where the time T until the secondary injection starts is calculated.
In step 309, the number nj of invalid injection operations that can be executed within the time T is calculated based on the above-described equations. Then, in step 311, the value of the invalid injection operation execution permission flag X described later is set to 1, and the current operation ends. When the value of X is set to 1, the execution of the invalid injection operation is permitted in the invalid injection operation execution operation (FIG. 4) described later.

On the other hand, if it is not the current timing for calculating nj in step 303, the operation is terminated without changing the value of the flag X. If it is determined in step 305 that the secondary fuel injection is not scheduled this time, the process proceeds to step 313, where the value of the number of invalid injections nj is set to a sufficiently large constant njk. End the operation. If the secondary fuel injection is not scheduled this time, there is no danger that the invalid injection operation and the secondary fuel injection will interfere with each other, so it is not necessary to stop the invalid injection operation. As described later, in the present embodiment, the value of nj is reduced by 1 each time the invalid injection operation is performed, and the invalid injection is stopped when 0 ≦ nj <1. Therefore, the value of njk in step 313 is set to n until the operation is performed next time and the determination in step 305 is performed again.
The value of j is set to a sufficiently large value so as not to be smaller than 1.

FIG. 4 is a flowchart for explaining the execution operation of the invalid injection operation. This operation is executed by the ECU 20 at regular intervals (an interval shorter than the invalid injection operation execution interval tint). When the operation of FIG. 4 starts, it is determined in step 401 whether or not the invalid injection operation is currently requested, that is, whether or not the invalid injection operation is necessary for stepping down the common rail based on the value of the flag XS.
The flag XS is set to 1 when the fuel cut operation is currently being performed and the common rail pressure is higher than the control target pressure (that is, when the common rail pressure-reducing operation due to the invalid injection operation is required) by an operation separately executed by the ECU 20. This flag is set and otherwise reset to 0.

When the value of the flag XS is not set to 1 in step 401, this operation ends immediately without executing step 403 and subsequent steps. In this case,
Since the common rail step-down operation is not required, the invalid injection operation is not performed. If XS = 1 in step 401, the process proceeds to step 403, in which it is determined whether the value of the invalid injection operation execution permission flag X is set to 1. If X = 1 in step 401, that is, since invalid injection has been requested and invalid injection execution has been permitted, next, in step 405, the invalid injection execution permission condition is determined again. If the execution permission condition is still satisfied, the value of the counter CTINT is decremented by one in step 407. Then, when CTINT ≦ 0 as a result of the countdown (step 409), an invalid injection operation is executed in step 411. Then, after the execution of the invalid injection operation, the value of the number nj of times the invalid injection operation can be executed is decreased by 1 in step 411, and the value of the counter CTINT is further reduced in step 415 to the initial value CT.
Set to INT ₀ and end the operation.

That is, in the present embodiment, step 401
As long as the conditions from 405 to 405 hold, the operation of FIG.
Each time TINT is executed ₀ times, the invalid injection operation is performed. Further, since this operation is executed at regular intervals, the invalid injection operation is executed at regular intervals. CTIN
T ₀ is the number of operation executions corresponding to the invalid injection operation execution interval tint. That is, in the present embodiment, the next invalid injection operation is set every time the invalid injection operation ends.

On the other hand, at step 413, the number of invalid injections nj
As a result, 0 ≦ nj <1 in step 405
In other words, the remaining
Because the number of executable times is less than one (0
≦ nj <1 is calculated in step 309 in FIG.
Go to step 417).
Reset the value of the execution permission flag X to 0 and end the operation
You. In this case, step 403 is performed from the next operation execution.
To step 413, and the executable number n
Only the value of j is decreased by one, but the step 411 is invalid.
No injection operation is performed. This allows for secondary fuel injection
Invalid injection operation in the affected area (Fig. 2, shaded area)
Will not be executed. When the engine speed is high,
Is calculated in step 309 because the time T becomes extremely short.
In some cases, the value of nj may be smaller than 1.
In this case, the invalid injection operation is immediately performed by step 405 in FIG.
Operation is stopped, from the reference time to the start of secondary fuel injection
During this period, the invalid injection operation is not performed. On the other hand,
When the secondary fuel injection is completed, the ECU 20
In the executed routine, the execution permission flag X is set to 1.
Is Therefore, when the secondary fuel injection ends,
Step 405 is executed after step 403
become. However, execution of the invalid injection operation in step 403
Is stopped (X = 0), step 413 is executed.
And the value of nj is decreasing,
When the injection ends and X = 1 in step 403
The value of nj is a negative value (nj <0). others
Therefore, after the end of the secondary fuel injection, the execution stop is released (X = 1).
If you still need to step down the common rail
(Ie, if XS = 1 in step 401),
Steps 407 to 415 follow steps 403 and 405
Will be executed. That is, in this case, the secondary fuel injection
When the time tint has elapsed since the end of the fuel injection (tint
Charge time t of the valve solenoid _chLonger time)
The invalid injection operation is restarted.

According to the present embodiment as described above, FIG.
By performing the operation in FIG. 4, when both the invalid injection operation and the secondary fuel injection interfere with each other during the execution, the invalid injection operation is temporarily stopped. Interference between the invalid injection operation and the secondary fuel injection is prevented without impairing the pressure drop.

[0044]

According to the invention described in each of the claims, it is possible to reduce the pressure in the accumulator chamber by the invalid injection operation of the fuel injection valve even when performing the secondary fuel injection. There is no need to provide any means for lowering the pressure of the chamber.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a schematic configuration of an embodiment in which the present invention is applied to an automobile diesel engine.

FIG. 2 is a timing chart illustrating an embodiment of the control of the invalid injection operation of the present invention.

FIG. 3 is a flowchart illustrating an embodiment of control of an invalid injection operation according to the present invention.

FIG. 4 is a flowchart illustrating an embodiment of control of an invalid injection operation according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Fuel injection valve 3 ... Common rail 10 ... Diesel engine 20 ... Electronic control unit (ECU) 37 ... Crank angle sensor

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 41/38 F02D 41/38 B (72) Inventor Isamu Goto 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor (72) Inventor Takashi Yamamoto 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Tomohiro Kaneko 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation F Term (reference) 3G091 AA18 BA00 BA14 CA18 CB02 CB03 EA03 EA07 EA30 FA05 FB12 3G301 HA02 HA04 KA26 LB04 LB11 LC01 LC10 MA11 MA19 MA23 MA26 NB11 NE23 PA17Z PB08A PB08Z PE01Z PE04Z PF03Z

Claims (2)

[Claims] An accumulator for storing pressurized fuel, a fuel injector for injecting fuel from the accumulator into an internal combustion engine, and a fuel injection controller for controlling the fuel injector to inject fuel into the engine. Wherein the fuel injection control means executes secondary fuel injection for injecting fuel into the engine at a predetermined time after the main fuel injection from the fuel injection valve as needed, Further, if necessary, an invalid injection operation without actual fuel injection of the fuel injection valve is performed at predetermined time intervals to reduce the pressure in the pressure accumulation chamber, and both the secondary fuel injection and the invalid injection operation are performed. When executing the fuel injection control, the invalid injection operation is stopped for a predetermined period before the execution of the secondary fuel injection. 2. The fuel injection control means calculates a time from a predetermined reference time to a start of the secondary fuel injection,
Claiming that the number of invalid injection operations that can be executed within the time is set, the invalid injection operation is stopped when the set number of invalid injection operations is performed, and the invalid injection operation stop after the end of the secondary fuel injection is released. Item 2. The fuel injection control device according to Item 1.