JP2000161171A - Accumulator type fuel injection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent engine trouble or the like by determining whether or not a selector valve installed to correspond to the fuel injection nozzle of each cylinder and adapted for changing fuel injection rate has failed and whether or not a pressure control valve for controlling the pressure of a low pressure accumulator has failed, and performing limp home mode control that limits an engine operating range, if they have failed. SOLUTION: Fuel pressurized by a fuel pump 1 is stored in a first accumulator 3 and supplied to a fuel injection nozzle 9 via a first control valve 5 and a fuel passage 10a and also to a second accumulator 4 to store it therein. The fuel pressure of the second accumulator 4 is controlled by a second control valve 34. When determining that the first control valve 5 or the second control valve 34 has failed, a control means 8 sets the delivery pressure of the fuel pump 1 at or below the allowable pressure of the second accumulator 4 to cause injection of fuel from the fuel injection nozzle 9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an accumulator type fuel injection device.

[0002]

2. Description of the Related Art As a fuel injection device for a diesel engine, a high pressure fuel accumulated in an accumulator is stably supplied to each cylinder of the engine to improve the engine performance in a wide operating range from a low speed range to a high speed range. There is a type fuel injection device (common rail system). Even when such a fuel injection device is used, if the fuel injection rate immediately after the start of fuel injection is excessive, rapid explosion combustion is performed at the beginning of combustion, which not only increases engine noise but also increases exhaust gas emissions. Nitrogen oxides (NOx) increase.

In order to solve such a problem, a pressure-accumulation type fuel injection device which injects fuel at a low fuel injection rate in an initial stage of each fuel injection cycle has been proposed. The fuel injection device according to this proposal selectively communicates, for example, a low-pressure accumulator for storing low-pressure fuel, a high-pressure accumulator for storing high-pressure fuel, and a low-pressure accumulator or a high-pressure accumulator to an injector (fuel injection nozzle). A switching valve for switching the fuel injection rate by controlling the fuel injection rate, and an on-off valve for controlling the fuel injection timing by connecting / disconnecting the pressure control chamber of the injector and the fuel tank.

[0004] With respect to the fuel pressure generation in the accumulator, for example, a low-pressure fuel and a high-pressure fuel are obtained by using a low-pressure fuel pump and a high-pressure fuel pump driven by an engine, respectively. There is one that obtains low-pressure fuel by regulating high-pressure fuel introduced into an accumulator (for example, JP-A-6-93936). A pressure-accumulation fuel injection device of the type that obtains low-pressure fuel of a low-pressure accumulator from high-pressure fuel of a high-pressure accumulator (for example, WO98 / 0906)
In 8), for example, the on-off valve for controlling the fuel injection timing, which is provided corresponding to the injector of each cylinder, is closed, and the switching valve for switching the fuel injection rate is switched to the low pressure side. The chamber (fuel pool) is filled with low-pressure fuel, and the injector is kept closed. When the fuel injection start time comes, the on-off valve is opened, the injector is opened, and low-pressure fuel is injected from the nozzle to reduce the pressure. Initial injection (hereinafter referred to as "low-pressure injection") is performed, and when the low-pressure injection period has elapsed, the switching valve is switched to the high-pressure side, and high-pressure fuel from the high-pressure accumulator is injected from the nozzle to perform high-pressure main injection (hereinafter, "high-pressure injection"). When the injection end time comes, the switching valve is switched to the low pressure side and the on-off valve is closed. That is, the switching valve switches between the low-pressure accumulator and the high-pressure accumulator during fuel injection to control the fuel injection waveform.

[0005] In the low-pressure accumulator, after the switching valve is closed, the high-pressure fuel accumulated between the switching valve and the fuel chamber of the injector is regulated to obtain low-pressure fuel. That is, the pressure control valve of the low-pressure accumulator connected to the fuel passage between the low-pressure accumulator and the fuel tank is duty-controlled so that the fuel pressure in the low-pressure accumulator becomes a predetermined pressure. The fuel is discharged to the fuel tank (open to the atmosphere).

[0006]

However, in the pressure accumulating type fuel injection device having the above-described structure in which the low pressure accumulator and the high pressure accumulator are switched during fuel injection to control the injection waveform, the pressure accumulator is installed corresponding to the injector of each cylinder. If the switching valve for switching the fuel injection rate is failed, for example, if the switching valve of one of the six cylinders or four of the four cylinders fails, the fuel injection pressure and the fuel injection amount of the cylinder will be reduced to the remaining other. Since the engine becomes abnormal as compared with the cylinder, the engine output is reduced, the torque fluctuation is increased, and the engine cannot be operated normally. Further, if the operation of the engine is continued in such an abnormal state, there is a problem that the engine and eventually the vehicle may be damaged due to an overload, a rise in the exhaust gas temperature and the like.

Further, when the pressure control valve installed in the low-pressure accumulator fails, the fuel pressure of the low-pressure accumulator increases when the valve closes, and eventually becomes equal to the fuel pressure of the high-pressure accumulator. As a result, high-pressure injection is performed from the early stage of injection, and the amount of fuel injection increases, resulting in overload operation. Therefore, if the engine is continued to operate in an abnormal state, the engine and eventually the vehicle may be damaged. Also, the low pressure accumulator
Since the allowable withstand pressure (allowable pressure) is set lower than that of the high-pressure accumulator, an excessive increase in the fuel pressure in the low-pressure accumulator may cause damage to the low-pressure accumulator, fuel leakage, and the like.

When the pressure control valve fails to open,
Since low-pressure injection becomes impossible and only high-pressure injection (main injection) is performed, the ignition timing is delayed, the exhaust sound level is increased, the torque is insufficient, and the engine is adversely affected. Further, in order to increase the pressure of the low-pressure accumulator, the high-pressure fuel supply pump repeats excessive fuel pumping, which may cause a failure of the high-pressure fuel supply pump.

Therefore, in the present invention, the failure determination of the switching valve for switching the fuel injection rate provided corresponding to the fuel injection nozzle of each cylinder and the failure determination of the pressure control valve for controlling the pressure of the low-pressure accumulator are performed. An object of the present invention is to provide a pressure-accumulation fuel injection device that performs limp home mode control in which an engine operation area is limited when a failure occurs, thereby preventing an engine failure or the like.

[0010]

According to a first aspect of the present invention, high-pressure fuel pressurized by a fuel pump is stored in a first accumulator, and a first control valve and a fuel passage are provided. The fuel pressure is supplied to a fuel injection nozzle that injects the fuel into the combustion chamber of the engine through a branch passage, and is connected to the fuel passage through a branch passage, and the second pressure is lower than the fuel pressure in the first accumulator.
It is supplied to the accumulator and stored. The fuel pressure of the second pressure accumulator is controlled by a second control valve that discharges the fuel in the second pressure accumulator to the atmosphere open side. The control means controls the opening of the first control valve so as to discharge the high-pressure fuel in the first accumulator toward the second accumulator, and sets the fuel pressure of the second accumulator to a set pressure. For this purpose, the second control valve is controlled to open.

When the control means determines that at least one of the plurality of first control valves has failed, or determines that the second control valve has failed in the closed state, the control means increases the discharge pressure of the fuel pump to the second accumulator pressure. Set the pressure below the allowable pressure of the vessel. As a result, the fuel pump can perform the fuel injection below the allowable pressure of the second accumulator. In the invention according to claim 2, when the control means determines that the second control valve has failed in the open state, the control means sets the discharge pressure of the fuel pump to be equal to or lower than the allowable pressure of the second accumulator, and Is set before the valve opening timing of the fuel injection nozzle. Thus, the fuel injection can be started at the valve opening timing of the fuel injection nozzle, and the delay in the injection timing caused by the inability to perform the low pressure injection can be prevented.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be illustratively described in detail below with reference to the drawings. FIG. 1 is a schematic configuration diagram of an accumulator type fuel injection device as an embodiment of the present invention,
FIG. 2 is a schematic diagram showing a connection between main elements of the fuel injection device shown in FIG. 1 and injectors of each cylinder of the engine.

In FIGS. 1 and 2, the accumulator type fuel injection device is mounted on, for example, an in-line six-cylinder diesel engine (not shown). The high-pressure fuel pump 1 is, for example, as shown in FIG. And two plunger pumps 20, each of which corresponds to the front three cylinders and the rear three cylinders of the in-line six-cylinder engine, respectively, and drives the front three cylinder plungers 21 and the rear three cylinder plungers 21. Each of the cams 22 has three peaks, and each plunger 21 performs three pumping strokes to feed the fuel while the high-pressure fuel pump shaft makes one rotation. Adjustment of the pressure feeding stroke
This is performed by adjusting the closing timing of the solenoid valve 23 provided on the discharge side of the plunger. While the solenoid valve 23 is open, the pressure feeding operation of the plunger pump 20 becomes invalid. I have. The solenoid valve 23 is controlled by an electronic control unit 8 described later.

Returning to FIG. 1, an electronic control unit (ECU) 8 as a control means of the accumulator type fuel injection device includes an engine speed Ne detected by an engine speed sensor 8a and an accelerator opening sensor (not shown). The pressure stroke is variably adjusted by controlling the solenoid valve 23 of the high-pressure fuel pump 1 in accordance with the accelerator pedal depression amount (accelerator opening degree) Acc detected by the control unit 3 and the high-pressure accumulator (first accumulator) 3. The pressure feeding stroke (discharge pressure) according to the fuel pressure P _HP detected by the provided pressure sensor (first fuel pressure detecting means) 3a.
Is feedback-controlled to obtain high-pressure fuel suitable for the operating state of the engine.

The fuel pressurized by the high-pressure fuel pump 1 is stored in the high-pressure accumulator 3. This high-pressure accumulator 3
It is common to each cylinder and communicates with the fuel passage 10a. In the middle of the fuel passage 10a, for example, a switching valve (first control valve) 5 for switching the fuel injection rate, which comprises a two-way solenoid valve, is used.
Is provided for each cylinder (FIG. 2), and a check valve 32 is provided immediately downstream of the switching valve 5 to allow fuel flow only from the upstream side to the downstream side.

The fuel passage 10a has a fuel passage 10b branched from the fuel passage 10a downstream of the check valve 32.
A common low-pressure accumulator (second accumulator) 4 is connected to each cylinder via the. A check valve 6 is provided in the middle of the fuel passage 10b.
And a bypass passage for bypassing the check valve 6, and an orifice 6a is provided in the bypass passage. The check valve 6 is connected between the low-pressure accumulator 4 and the fuel passage 10.
The fuel flow is allowed only in the direction a. When the fuel pressure in the fuel passage 10a is higher than the fuel pressure in the fuel passage 10b,
The fuel in the fuel passage 10a flows into the fuel passage 10b through the orifice 6a, and further flows into the low-pressure accumulator 4. A pressure control valve (second control valve) 34 that operates under the control of the electronic control unit 8 and controls the fuel pressure of the low-pressure accumulator 4 is provided between the low-pressure accumulator 4 and the fuel tank 17 in the fuel passage 10b. Have been. As shown in FIG. 2, the low-pressure accumulator 4 has a pressure sensor 4a for detecting a fuel pressure P _LP in the low-pressure accumulator 4.
(Second fuel pressure detecting means) is provided.

The electronic control unit 8 detects the fuel pressure in the low-pressure accumulator 4 by the pressure sensor 4a so as to be a pressure suitable for the engine operating state represented by the engine speed Ne and the accelerator pedal depression amount Acc. The pressure control valve 34 is controlled based on the actual pressure P _LP thus obtained. An injector 9 as a fuel injection nozzle provided in each cylinder of the engine has a pressure control chamber 11 and a fuel chamber (fuel pool) 12 connected to a fuel passage 10a via an orifice 15, and the pressure control chamber 11 Is connected to a fuel tank 17 via an orifice 16 and a fuel return passage 10c. An on-off valve 7 for controlling the fuel injection timing, which is composed of, for example, a two-way solenoid valve, is connected in the middle of the fuel return passage 10c. Note that the on-off valve 7 may be installed in the injector.

The injector 9 has a needle valve 13 for opening and closing a nozzle (injection hole) 9a, and a hydraulic piston 14 slidably housed in the pressure control chamber 11. The needle valve 13 is a spring (FIG. (Not shown) to the nozzle 9a side to close the valve. When fuel is supplied from the fuel passage 10a to the pressure control chamber 11 and the fuel chamber 12 and the on-off valve 7 for controlling the injection timing is closed, the resultant force of the spring force of the spring and the fuel pressure is adjusted by the needle valve 13. In addition, the needle valve 13 closes the nozzle 9a against the fuel pressure in the fuel chamber 12. When the on-off valve 7 opens and the fuel in the pressure control chamber 11 is discharged to the fuel tank 17 side (open to the atmosphere), the needle valve 13 resists the spring force of the spring due to the fuel pressure in the fuel chamber 12. And hydraulic piston 1
The nozzle 9a is opened by moving to the side 4 and fuel in the fuel chamber 12 is injected from the nozzle 9a into the combustion chamber of the engine.

The operation of the fuel injection device having the above configuration in the normal mode will be described below. Under the control of the electronic control unit 8, the fuel pressure in the high-pressure accumulator 3 and the fuel pressure in the low-pressure accumulator 4 are controlled so as to conform to the engine operating state, and the engine operating state (engine speed, accelerator pedal depression amount) is controlled. Etc.), a fuel injection period (fuel injection start / end timing) and a low pressure injection period are set.

As shown in FIG. 4, the switching valve 5 and the on-off valve 7 are both closed until the fuel injection start timing arrives, and the low pressure fuel passage 10a downstream of the switching valve 5 is supplied to the fuel passage 10a. Low-pressure fuel is supplied from the pressure accumulator 4, and the low-pressure fuel is supplied to the pressure control chamber 11 and the fuel chamber 12 of the injector 9. When the on-off valve 7 is closed, the fuel pressure supplied into the pressure control chamber 11 is applied to the needle valve 13 via the hydraulic piston 14, and the nozzle 9 a
Is closed and the valve is closed.

At the fuel injection start timing, only the on-off valve 7 is opened, and the low-pressure fuel in the pressure control chamber 11 of the injector 9 is discharged to the fuel tank 17 through the orifice 16 and the fuel return passage 10c. As a result, when the resultant force of the fuel pressure applied to the needle valve 13 via the hydraulic piston 14 and the spring force of the spring becomes smaller than the fuel pressure in the fuel chamber 12 acting to push up the needle valve 13, the needle valve 13 Rises to open the nozzle 9a, and low-pressure fuel is injected from the nozzle 9a. That is, low-pressure injection is performed at a relatively low fuel injection rate (fuel injection amount per unit time) at the beginning of injection. By this low-pressure injection, the combustion in the initial stage of the fuel injection period is performed relatively slowly, and the amount of NOx in the exhaust gas is reduced.

When a predetermined time has elapsed after the start of the low pressure injection, the switching valve 5 for switching the injection rate is opened while the on-off valve 7 for controlling the injection timing is opened, and the fuel chamber 12 is opened. High-pressure fuel is supplied, and high-pressure fuel is injected from the injector 9. That is, high-pressure injection is performed at an injection rate larger than the fuel injection rate at low-pressure injection. When the fuel injection ends, the on-off valve 7 for controlling the injection timing is closed, and the high-pressure fuel supplied from the fuel passage 10a to the pressure control chamber 11 through the orifice 15 is supplied to the needle valve 13 via the hydraulic piston 14. Acting, the needle valve 13 closes the nozzle 9a, and the fuel injection from the nozzle 9a ends. At the end of fuel injection, the fuel injection rate falls rapidly, and the amount of black smoke (smoke) and particulates (particulate matter PM) emitted from the engine is reduced. The switching valve 5 for switching the injection rate is closed at the same time as the closing of the on-off valve 7 at the fuel injection end timing, or is closed when a predetermined time has elapsed from the fuel injection timing end timing.

As shown in FIG. 5, between the fuel chamber 12 of the injector 9 and the switching valve 5 for switching the injection rate, the high-pressure fuel in the fuel passage 10a passes through the orifice 6a of the fuel passage 10b to the low-pressure accumulator 4. As a result, the fuel pressure in the fuel passage 10a gradually decreases from the end of the fuel injection in each fuel injection cycle, and the pressure control is continued until the fuel injection in the next fuel injection cycle is started. Valve 3
The fuel pressure is reduced to the fuel pressure suitable for the low-pressure injection set by 4, and the injection rate in the next low-pressure injection becomes required.

As described above, when the switching valve for switching the fuel injection rate installed corresponding to the injector of each cylinder fails, for example, the switching valve 5- of the first cylinder in the six cylinders shown in FIG. If 1 fails, the fuel injection pressure and fuel injection amount to the first cylinder become abnormal as compared with the other cylinders, so that the engine output decreases, torque fluctuation increases, etc. Will not be able to run the engine.

That is, in the control of the injector / switching valve, the injection waveform when the switching valve 5-1 of the first cylinder fails in the closed state as shown in FIG. 6 shows the injection waveform of another cylinder in which the switching valve is normal. The injection waveform (shown by the dotted line) is abnormal injection of only low-pressure injection in which high-pressure injection is not performed. Therefore, the switching valve 5
Only the first cylinder of -1 cannot perform high-pressure injection, and the fuel injection amount is smaller than in the other cylinders. Thus, one out of six cylinders
Since the fuel amount is reduced only in the cylinder, the torque fluctuation increases, and the engine vibration increases. FIG. 6 is a timing chart showing the fuel injection waveform and the driving of the injector 9 and the switching valve 5-1 when the switching valve 5-1 of FIG. 2 fails in the closed state.

When the switching valve 5-1 is out of order and fails, as shown in FIG. 7, the injection waveform of the cylinder in which the switching valve is normal (shown by a dotted line) is low pressure injection. It becomes a waveform of only the high-pressure injection that is not performed. Therefore, the switching valve 5-1
Only the first cylinder has a larger amount of fuel than the other cylinders. As described above, since the fuel amount is not large in only one of the six cylinders, the torque fluctuation increases, and the engine vibration increases. In addition, the switching valve 5-1 injects fuel in excess of the set fuel amount only in the failed first cylinder, so that only the first cylinder is overloaded and the engine may be seized. FIG.
3 is a timing chart showing a fuel injection waveform and driving of the injector 9 and the switching valve 5-1 when the switching valve 5-1 in FIG. 2 fails in the open state.

Thus, even if any of the switching valves 5 fails in either the closed state or the open state, the combination of low-pressure injection and high-pressure injection cannot be performed, and the switching valve cannot be switched to another cylinder in which the switching valve is normal. The injection amount becomes abnormal. Therefore, in the pressure accumulating fuel injection device of the present invention, the electronic control unit 8 executes a switching valve failure determination routine shown in FIG. 9 at a predetermined cycle. In this determination routine, it is determined whether or not the switching valve 5 for switching the injection rate for switching between the injection of the high-pressure fuel and the low-pressure fuel is normal (step S1). If it is normal, the process shifts to the normal control mode (step S2). If a failure has occurred, the control shifts to a failure control mode (limp home mode) (step S3).

The failure of the switching valve 5 in step S1 is determined by monitoring the load state of the pressure control valve 34 for controlling the fuel pressure of the low-pressure accumulator 4 by the electronic control unit 8.
The failure determination of the switching valve 5 is performed in two cases, that is, a failure in the closed state and a failure in the open state. If the switching valve 5-1 fails in the closed state, the supply of high-pressure fuel from the fuel passage 10a to the low-pressure accumulator 4 is reduced by the amount supplied through the switching valve 5-1. Therefore, the pressure control valve 34 for controlling the fuel pressure of the low-pressure accumulator 4
The duty ratio (valve opening rate) of (FIGS. 1 and 2) is made smaller than the normal state (the valve closing time is made longer) and the fuel tank 17 is opened.
If the amount of fuel discharged to the low pressure accumulator 4 is not reduced, the fuel pressure of the low pressure accumulator 4 does not reach the set pressure. Therefore, the pressure control valve 34
Duty ratio (load) becomes smaller.

When the switching valve 5-1 fails in the open state, the supply amount of high-pressure fuel from the fuel passage 10a to the low-pressure accumulator 4 is increased by the amount supplied through the switching valve 5-1. In order to increase the fuel pressure, the duty ratio of the pressure control valve 34 for controlling the fuel pressure of the low-pressure accumulator 4 is made larger than that in the normal state (by increasing the valve opening time), and a large amount of fuel is supplied to the fuel tank 17.
, The fuel pressure of the low-pressure accumulator 4 does not reach the set pressure. Therefore, the duty ratio (load) of the pressure control valve 34 increases.

FIG. 10 shows the relationship between the indicated pressure of the low-pressure accumulator 4 and the duty ratio (load) of the pressure control valve 34. FIG.
At 0, the solid line indicates the reference value (theoretical valve opening ratio) of the duty ratio of the pressure control valve 34 when the switching valve 5 is in a normal state, and the duty ratio allowable value (hysteresis) is provided on both sides.
Is set as the reference area I. The lower region II of the reference region I is a region where the duty ratio of the pressure control valve 34 is small, that is, the load is small, and the upper region III is a region where the duty ratio of the pressure control valve 34 is large, that is, the load is large. .

The electronic control unit 8 monitors the duty ratio (load) of the pressure control valve 34, and when the duty ratio is in the area II that deviates from the reference area I in FIG. It is determined that the switching valve 5 is open and malfunctions when the switching valve 5 is in the region III. The failure of the switching valve 5 includes a mechanical failure such as a stick of the spool due to exposure to high-pressure fuel, and an electrical failure due to disconnection of the solenoid. In addition, there is a failure due to clogging of the orifice 6a. When the solenoid of the switching valve 5 is disconnected, the electronic control unit 8
The failure of the switching valve 5 is determined by the disconnection determination.

The electronic control unit 8 controls the switching valve 5 for switching the fuel injection amount, the injection pressure, the injector 9 and the fuel injection rate in the failure control mode (limp home mode) of the switching valve in step S3 in FIG. Each control map is switched and controlled for the failure mode. That is, as shown by the solid line in FIG. 11, the fuel injection amount control limits the maximum injection amount and the maximum engine speed (maximum value) to the normal mode (maximum value) indicated by the dotted line. FIG. 11 is a characteristic diagram showing a relationship between the engine speed and the fuel injection amount.

Further, the electronic control unit 8 controls the maximum pressure (fuel pressure) of the high-pressure accumulator 3 and the low-pressure accumulator 4 to a predetermined pressure (hereinafter referred to as "set pressure") as shown by a solid line in FIG.
This set pressure is lower than the fuel pressure of the high-pressure accumulator 4 at the time of normal control, the maximum pressure is higher than the fuel pressure of the low-pressure accumulator 4 at the time of normal control, and
Is not more than the allowable withstand pressure (allowable pressure). This set pressure controls the fuel pressure of the high-pressure accumulator 3 by adjusting the effective section of the pressure-feeding stroke of the plunger 21 (FIG. 1) of the high-pressure fuel pump 1, and controls the duty ratio of the pressure control valve 34 to reduce the low pressure. The fuel pressure of the accumulator 4 is controlled so that the high pressure accumulator 3 and the low pressure accumulator 4 have the same fuel pressure. By setting the maximum pressure (fuel pressure) of the high-pressure accumulator 3 to be equal to or less than the allowable withstand pressure of the low-pressure accumulator 4, the low-pressure accumulator 4
Damage and fuel leakage are prevented. FIG. 12 is a characteristic diagram showing a relationship between the engine speed and each fuel pressure of the high-pressure accumulator 3 and the low-pressure accumulator 4.

As described above, by setting the maximum pressure (fuel pressure) of the high-pressure accumulator 3 to be equal to or less than the allowable withstand pressure of the low-pressure accumulator 4, the cylinder in which the switching valve 5 has failed and the other cylinder in which the switching valve 5 is normal can be used. The fuel injection pressure becomes the same, the torque difference between cylinders disappears,
Torque fluctuation is suppressed, and engine vibration is suppressed. FIG. 8 shows a fuel injection waveform in the failure mode of the switching valve 5,
4 is a timing chart showing driving of the injector 9 and the switching valve 5. As shown in FIG. 8, control of the on-off valve 7 for controlling the valve opening timing of the injector 9, that is, the injection timing, is simplified by using the same map as the normal control.
Further, the normal valve opening timing of the switching valve 5 is set to be advanced (advanced) with respect to the valve opening timing of the injector 9 (valve opening timing of the on-off valve 7). Accordingly, when the switching valve 5 fails to close, the fuel pressure (P _HP ) of the high-pressure accumulator 3 = the fuel pressure (P P) of the low-pressure accumulator 4
_LP ), the cylinder in which the switching valve 5 has a valve-closing failure is supplied from the low-pressure accumulator 4 with the same pressure as the fuel in the other switching valve 5 and the normal cylinder. The injection waveform of the cylinder can be made uniform. Further, when a certain switching valve 5 fails to open, the switching valve 5 is open in the cylinder in which the other switching valve 5 is normal during the entire injection period, and the switching valve 5 is opened. Since the conditions are the same as those of the cylinder with a valve failure,
The injection waveforms of all cylinders can be made uniform.

As described above, the failure of the switching valve 5 for switching the fuel injection rate is determined by the electronic control unit 8, and when the failure occurs, the limp home mode is set, whereby the engine body is damaged, and the engine body is overloaded and the exhaust gas is exhausted. The vehicle can be prevented from being damaged due to a rise in temperature or the like. In addition, when the switching valve fails, by performing appropriate control in the limp home mode, it becomes possible to suppress overload operation of the engine, fluctuations in rotation, and the like, and to travel to a repair shop by itself.

If the pressure control valve 34 for controlling the pressure of the low-pressure accumulator 4 fails, the fuel pressure of the low-pressure accumulator 4 increases when the valve closes, and finally, the fuel pressure of the high-pressure accumulator 3 increases. Become equal. As shown in FIG. 13, the injection waveform when the pressure control valve 34 fails in the closed state is different from the abnormal injection of only the high-pressure injection from the initial stage of the injection with respect to the case where the pressure control valve 34 is normal (shown by a dotted line). Become. Therefore, since the fuel injection amount increases to cause overload operation, if the engine operation is continued in this abnormal state, the engine and eventually the vehicle may be damaged. Further, since the low-pressure accumulator 4 has a lower allowable withstand pressure than the high-pressure accumulator 3, an excessive increase in the fuel pressure in the low-pressure accumulator 4 may cause damage to the low-pressure accumulator 4 and fuel leakage. And so on. FIG. 13 shows a fuel injection waveform when the pressure control valve 34 fails in the closed state,
4 is a timing chart showing driving of the injector 9 and the switching valve 5.

When the pressure control valve 34 fails to open, low-pressure injection becomes impossible, and the injection waveform is changed to the low-pressure injection (shown by a dotted line) as shown in FIG. The waveform is only the high-pressure injection (main injection) in which the initial injection is not performed. As a result, the ignition timing is delayed, the exhaust gas temperature rises, and the torque becomes insufficient, which adversely affects the engine. Also, in order to increase the pressure of the low-pressure accumulator 4,
There is a possibility that the high-pressure fuel pump 1 repeats excessive fuel pumping, causing the high-pressure fuel pump 1 to fail. FIG. 14 shows a fuel injection waveform when the pressure control valve 34 fails in the open state,
4 is a timing chart showing driving of the injector 9 and the switching valve 5.

Thus, even if the pressure control valve 34 fails in either the closed state or the open state, the combination of low-pressure injection and high-pressure injection cannot be performed. The injection amount becomes abnormal. Therefore, in the accumulator type fuel injection device of the present invention, the electronic control unit 8
The routine for determining the failure of the pressure control valve of the low-pressure accumulator shown in FIG. In this determination routine, it is determined whether or not the pressure control valve 34 that controls the fuel pressure of the low-pressure accumulator 4 is normal (step S11). If the pressure control valve 34 is normal, the process shifts to the normal control mode (step S12), and it is broken. In some cases, the mode shifts to the failure control mode (limp home mode) (step S13).

The failure of the pressure control valve 34 in step S11 is determined by the electronic control unit 8 between the actual pressure detected by the pressure sensor 4a detecting the fuel pressure of the low-pressure accumulator 4 and the pressure indicated by the electronic control unit 8. The determination is made by monitoring the time during which the differential pressure equal to or greater than a certain fixed value continues. The failure determination of the pressure control valve 34 is performed in two cases, that is, when the valve is in the closed state and when the valve is in the open state.

When the pressure control valve 34 fails in the closed state, the high-pressure fuel supplied from the fuel passage 10a to the low-pressure accumulator 4 is not discharged to the fuel tank 7 side (open to the atmosphere). The fuel pressure in the low-pressure accumulator 4 increases. When the (actual pressure) of the low-pressure accumulator 4 detected by the pressure sensor 4a is higher than the (instruction pressure + α) (actual pressure> instruction pressure + α) for a certain period of time, the electronic control unit 8 determines the pressure. It is determined that the control valve 34 has failed in the closed state.
The certain time is a follow-up time for accurately monitoring the pressure difference.

When the pressure control valve 34 fails in the open state, all of the high-pressure fuel supplied from the fuel passage 10a to the low-pressure accumulator 4 is discharged to the fuel tank 7 side (open to atmosphere). As a result, the fuel pressure in the low-pressure accumulator 4 decreases. When the (actual pressure) of the low-pressure accumulator 4 detected by the pressure sensor 4a is lower than the (instruction pressure−α) (actual pressure <instruction pressure−α) for a certain period of time or longer, It is determined that the pressure control valve 34 has failed in the open state.

FIG. 16 shows the relationship between the indicated pressure of the low-pressure accumulator 4 and the output (actual pressure) of the pressure sensor 4a. In FIG. 16, a solid line indicates a reference value in a normal state of the pressure control valve 34, and an allowable value (hysteresis) is set on both sides of the reference value, which is a reference region I. Area VI below reference area V
Is the area where the actual pressure is smaller than the indicated pressure, the upper area VI
I is a region where the actual pressure is larger than the indicated pressure.

The electronic control unit 8 monitors the actual pressure and the instructed pressure (set pressure). When the electronic control unit 8 is in the area VI that deviates from the reference area V in FIG. It is determined that the pressure control valve 34 is in the closed state and has failed when the pressure control valve 34 is in the region VII. The failure of the pressure control valve 34 includes a mechanical failure such as a stick of the spool and an electrical failure due to disconnection of the solenoid. When the solenoid of the pressure control valve 34 is disconnected, the electronic control unit 8 determines the failure of the pressure control valve 34 by the disconnection determination.

The electronic control unit 8 executes step S1 in FIG.
In the failure control mode (limp home mode) of the third pressure control valve 34, the control map of the switching valve 5 for switching and controlling the fuel injection amount, the injection pressure, the injector 9 and the fuel injection rate is switched and controlled for the failure mode. I do. That is,
As shown by the solid line in FIG. 11, the fuel injection amount control limits the maximum injection amount and the maximum engine speed (maximum value) with respect to the normal mode (maximum value) indicated by the dotted line.

Further, the electronic control unit 8 controls the fuel pressure of the high-pressure accumulator 3 and the low-pressure accumulator 4 to a predetermined set pressure as shown by a solid line in FIG. I do. This set pressure is lower than the fuel pressure of the high-pressure accumulator 4 during normal control, the maximum pressure is higher than the fuel pressure of the low-pressure accumulator 4 during normal control, and the allowable pressure of the low-pressure accumulator 4 ( By setting the pressure to be equal to or less than the allowable pressure, damage to the low-pressure accumulator and fuel leakage when the pressure control valve 34 fails can be prevented. This set pressure is equal to the high pressure fuel pump 1
The pressure (fuel pressure) of the high-pressure accumulator 3 is controlled by adjusting the effective section of the pressure feed stroke of the plunger 21 (FIG. 1). Accordingly, when the pressure control valve 34 fails to close, the pressures of the high-pressure accumulator 3 and the low-pressure accumulator 4 become the same. When the pressure control valve 34 fails to open, only the high-pressure accumulator 3 has a predetermined pressure, and the low-pressure accumulator 4 has a value lower than the set pressure.
For example, the pressure is almost equal to the atmospheric pressure.

In the failure mode of the pressure control valve 34, the injector 9 and the switching valve 5 are driven by the switching valve 5 described above.
(Switching valve 5-1) fails. That is, as shown in FIG. 8, the control of the opening / closing valve 7 for controlling the valve opening timing of the injector 9, that is, the injection timing, is simplified by using the same map as the normal control. Further, the valve opening timing of the switching valve 5 is set in a direction (advance angle) that is more advanced than the valve opening timing of the injector 9 (valve opening timing of the on-off valve 7). Thus, fuel injection can be started at the valve opening timing of the injector 9 regardless of whether the pressure control valve 34 fails to close the valve or fails to open the valve. Therefore, the pressure of the high-pressure accumulator 3 is suppressed (and the fuel pressure (P _HP ) of the high-pressure accumulator 3 = the fuel pressure (P
_In combination with _LP ) and control), when the valve closing failure of the pressure control valve 34 occurs, the excessive injection amount is prevented, and when the valve opening fails, the delay of the injection timing is prevented.

As described above, the failure of the pressure control valve 34 for controlling the pressure of the low-pressure accumulator 4 is determined by the electronic control unit 8, and when the failure occurs, the limp home mode is set.
It is possible to avoid damage to the engine main body, and furthermore, damage to the vehicle due to overload operation of the engine main body, increase in exhaust temperature, and the like. In addition, when the pressure control valve 34 fails, by performing appropriate control in the limp home mode, it becomes possible to suppress overload operation of the engine, fluctuations in rotation, and the like, and to travel to a repair shop by itself.

[0048]

According to the present invention, according to the first aspect of the present invention,
When the first control valve fails in the closed state, high-pressure injection of the cylinder corresponding to the failed first control valve is not performed, but the fuel pressure discharged from the normal first control valve (high-pressure fuel pump The pressure in the fuel passage is always maintained at a certain fuel pressure equal to or lower than the second accumulator allowable pressure, and corresponds to the failed first control valve. Even in the cylinder set as described above, the allowable pressure injection can be performed from the time when the injection nozzle is opened.

If the first control valve fails in the open state, only high-pressure injection is performed in all cylinders.
A pressure higher than the allowable pressure is applied to the accumulator, but in order to prevent this, a fuel injection with a pressure equal to or lower than the allowable pressure of the second accumulator is supplied by the high-pressure fuel pump. Further, when the second control valve fails in the closed state, the fuel of the second accumulator cannot be controlled,
In order to prevent high pressure, a high pressure fuel pump supplies fuel injection at a pressure equal to or lower than the allowable pressure of the second accumulator. As a result, failure of the engine, damage to the vehicle, and the like can be prevented.

According to the second aspect of the present invention, when the second control valve fails in the open state, only high-pressure injection is performed in all cylinders, and a pressure higher than the allowable pressure is applied to the second accumulator. However, in order to prevent this, the high-pressure fuel pump supplies fuel injection that is equal to or less than the allowable pressure of the second accumulator. Further, when the second control valve fails in the closed state, the fuel in the second pressure accumulator cannot be controlled and becomes high pressure. Fuel injection below the allowable pressure is supplied. As a result, failure of the engine, damage to the vehicle, and the like can be prevented.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a pressure accumulating fuel injection device according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing connection between main elements of the fuel injection device shown in FIG. 1 and injectors of each cylinder of the engine.

FIG. 3 is a schematic view of the high-pressure fuel pump shown in FIG.

FIG. 4 is a diagram showing a change in the injection rate over time and a change in each open / close state of a switching valve for switching the injection rate and an on-off valve for controlling the injection timing in one fuel injection cycle performed in the normal mode. is there.

FIG. 5 is a diagram showing a change in fuel pressure in a fuel passage between an injector and a switching valve over time in one fuel injection cycle performed in a normal mode.

FIG. 6 is a timing chart showing a fuel injection waveform and driving of the injector and the switching valve when the switching valve fails in a closed state.

FIG. 7 is a timing chart showing a fuel injection waveform and driving of the injector and the switching valve when the switching valve fails in an open state.

FIG. 8 shows a fuel injection waveform in a failure mode of the switching valve,
5 is a timing chart showing driving of an injector and a switching valve.

9 is a flowchart of a switching valve failure determination routine of the accumulator type fuel injection device shown in FIG.

FIG. 10 is a characteristic diagram showing a relationship between a command pressure of a low-pressure accumulator and a duty ratio (load) of a pressure control valve.

FIG. 11 is a characteristic diagram showing a relationship between an engine speed and a fuel injection amount.

FIG. 12 is a characteristic diagram showing a relationship between an engine speed and pressures (fuel pressures) of high-pressure and low-pressure accumulators.

FIG. 13 is a timing chart showing the fuel injection waveform and the driving of the injector and the switching valve when the pressure control valve fails in the closed state.

FIG. 14 is a timing chart showing a fuel injection waveform and driving of an injector and a switching valve when a pressure control valve fails in an open state.

15 is a flowchart of a switching valve failure determination routine of the pressure accumulating fuel injection device shown in FIG.

FIG. 16 is a characteristic diagram showing a relationship between a command pressure of a low-pressure accumulator and an actual pressure.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 high-pressure fuel pump 3 high-pressure accumulator (first accumulator) 4 low-pressure accumulator (second accumulator) 3a pressure sensor (first fuel pressure detecting means) 4a pressure sensor (second fuel pressure detecting means) 5 high-pressure / low-pressure accumulator (Fuel injection rate) Switching valve (first control valve) 7 Injection timing control opening / closing valve 8 Electronic control device (control means) 9 Injector (fuel injection nozzle) 10a, 10b Fuel passage 20 Plunger pump 21 Plunger 22 Cam 34 Low pressure accumulator pressure control valve (second control valve)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02M 63/00 F02M 63/00 CF F term (Reference) 3G066 AA07 AB02 AC01 AC09 AD12 BA12 BA24 BA25 BA33 CA01S CA09 CA20U CB07U CB09 CB11 CB12 CB16 CC06T CC08T CC14 CC26 CC64T CC66 CC67 CC68U CC70 CD26 CE02 CE13 CE22 DA04 DA11 DA12 DA13 DA14 DA16 DC04 DC09 DC18 3G301 HA02 HA04 HA06 JA05 JA24 JA25 JB02 JB08 LB06 LC01 MA11 MA18ZZZ03

Claims (2)

[Claims] 1. A first accumulator for storing high-pressure fuel pressurized by a fuel pump, a plurality of fuel passages extending from the first accumulator toward each cylinder, and an end of the fuel passage. And a plurality of first control valves disposed in each of the fuel passages for controlling discharge of high-pressure fuel in the first accumulator to a downstream side of the fuel passage. A second pressure accumulator that stores fuel at a lower pressure than high-pressure fuel in the first pressure accumulator and is connected to the fuel passage downstream of the first control valve via a branch passage; A second control valve for controlling discharge of fuel in the chamber to the atmosphere open side; and, during normal operation, opening the first control valve during the opening period of the fuel injection nozzle, and closing the fuel injection nozzle. And performing control to close the first control valve in accordance with the valve. When it is determined that at least one of the plurality of first control valves has failed, or when it has been determined that the second control valve has failed in a closed state, the discharge pressure of the fuel pump is stored in the second pressure accumulator. And a fuel control means for setting the pressure to be equal to or lower than the allowable pressure of the fuel injector. 2. A first accumulator for storing high-pressure fuel pressurized by a fuel pump, a plurality of fuel passages extending from the first accumulator toward each cylinder, and an end of the fuel passage. And a plurality of first control valves disposed in each of the fuel passages for controlling discharge of high-pressure fuel in the first accumulator to a downstream side of the fuel passage. A second pressure accumulator that stores fuel at a lower pressure than high-pressure fuel in the first pressure accumulator and is connected to the fuel passage downstream of the first control valve via a branch passage; A second control valve for controlling the discharge of fuel in the vessel to the atmosphere open side, a throttle disposed in a branch passage upstream of the second control valve, and a middle of a valve opening period of the fuel injection nozzle during a normal operation. Opens the first control valve and closes the fuel injection nozzle. Control to close the first control valve in accordance with the time, and when it is determined that the second control valve has failed in the open state, the discharge pressure of the fuel pump is set to the allowable pressure of the second accumulator. And a fuel control means for setting the opening timing of the other first control valve before the opening timing of the fuel injection nozzle.