JP5891831B2 - Method for controlling idling stop of internal combustion engine - Google Patents

Description

  The present invention relates to an idling stop control method for an internal combustion engine, and more specifically, an internal combustion engine that can restart an engine at an idling stop more quickly than before without increasing combustion noise at the time of restarting. The present invention relates to an engine idling stop control method.

  In recent years, automobile engines have been equipped with a so-called idling stop mechanism that automatically stops the engine when the vehicle is stopped and automatically restarts the engine when the vehicle is started from the viewpoint of saving fuel consumption and preventing environmental deterioration caused by exhaust gas. It has become so. Specifically, when the engine stop request is issued, the fuel supply to the engine is stopped, and when the engine restart request is issued, the fuel supply is restarted and the engine can be restarted by the starter. This is automatically performed (see, for example, Patent Document 1).

  By the way, in general, a fuel injection system for a diesel engine uses a common rail system in which fuel that is pumped and stored in a common rail by a high-pressure pump is injected into a cylinder by an injection nozzle. In this common rail system, the ECU that controls the engine monitors the value of the pressure sensor installed on the common rail and adjusts the high pressure pump so that the common rail pressure (fuel pressure) becomes an appropriate target pressure that changes according to the operating conditions. The flow control valve interposed between the common rail is controlled. This high pressure pump is driven in conjunction with the output of the engine.

  When the engine is restarted, in order for the fuel stored in the common rail to be injected into the cylinder and burned, not only the fuel pressure required for the fuel to burn, but also for the stable operation of the injection nozzle A minimum pressure Ps is required. As described above, the fuel pressure in the common rail depends on the pumping amount of the high-pressure pump. However, since the high-pressure pump is linked to the engine output, the fuel pressure is increased to the minimum pressure Ps until the engine speed increases. It is difficult. The fuel stored in the common rail leaks outside due to insufficient pressure sealing around the hydraulic operation circuit of the injection nozzle while the engine is stopped, so that the fuel pressure becomes almost zero. Therefore, the fuel pressure cannot be maintained at the minimum pressure Ps from when the engine is stopped to when it is restarted.

  Therefore, when the engine is restarted, it is necessary to rotate the engine for a certain period in order to ensure the minimum pressure Ps at which the fuel is stably injected. However, if the engine is rotated in this way, a time loss occurs between the time when the restart request is generated and the time when the engine is restarted. End up.

  In order to eliminate the driver's feeling of stickiness, it is desirable to start the combustion of fuel from the first compression stroke when the engine is restarted. However, the driving force of the starter that cranks the engine has a problem that the fuel pressure that has become almost zero when the engine is stopped cannot be increased to the minimum pressure Ps. In order to solve such problems, the target pressure of the common rail pressure is increased at the same time as the engine stop request is generated, thereby increasing the pumping amount of the high-pressure pump and maintaining the required fuel pressure until the restart. It is possible.

  However, if the target pressure of the common rail pressure is increased in this way, the combustion pressure rises excessively, and the combustion noise at the time of restart may increase.

JP 2001-173546 A

  An object of the present invention is to provide an idling stop control method for an internal combustion engine that can perform engine restart at the time of idling stop more quickly than before without increasing combustion noise at the time of restart. .

The idling stop control method for an internal combustion engine according to the present invention that achieves the above-described object is achieved by storing fuel that has been boosted to a target pressure by a high-pressure pump that rotates in conjunction with the crankshaft of the engine in a common rail, and storing the stored fuel. An idling stop control method for an internal combustion engine having a common rail system for injecting into a cylinder through an injection nozzle, wherein when the engine stop request is generated, the target pressure is increased to a maximum allowable pressure of the common rail system , Thereafter, when a restart request occurs, the pressure of the common rail is compared with the minimum pressure Ps required for fuel to be injected from the injection nozzle and burned in the cylinder, and the common rail pressure is compared. If it is higher, lower the common rail pressure until it reaches the minimum pressure Ps. It is characterized in that the restarting of the engine from.

The common rail pressure is decreased until the minimum pressure Ps is reached by opening and closing the actuator in the injection nozzle instantaneously and intermittently to the extent that fuel does not inject into the cylinder, or a pressure relief valve on the common rail. It is desirable to provide it by opening and closing the pressure relief valve intermittently.

According to the idling stop control method for an internal combustion engine of the present invention, when an engine stop request is generated, the common rail pressure target pressure is increased to the maximum allowable pressure of the common rail system , and then a restart request is generated. Since the common rail is depressurized, the common rail pressure is reduced to the minimum pressure Ps, which is the pressure required for the fuel to be injected from the injection nozzle and burned in the cylinder. Since the fuel is combusted in the cylinder from the first compression stroke and the combustion pressure does not increase excessively, the engine can be restarted more quickly than before without increasing the combustion noise at the time of restart.

It is a block diagram of the idling stop system of an internal combustion engine. It is a flowchart explaining the control method of the idling stop system of the internal combustion engine which consists of embodiment of this invention. It is a graph which shows a time-dependent change of the engine rotational speed and the common rail pressure in the control method of the idling stop system of the internal combustion engine which consists of embodiment of this invention. It is a block diagram of another example of the idling stop system of an internal combustion engine. It is a graph which shows the characteristic of the actuator of an injection nozzle. It is a flowchart explaining the control method of the idling stop system of the internal combustion engine which consists of a reference example of this invention. It is a graph which shows the example of the map for high pressure fuel injection.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows an idling stop system for an internal combustion engine that implements the control method for idling stop of the internal combustion engine of the present invention.

  This idling stop system for an internal combustion engine includes an engine 2 driven by fuel supplied from a fuel tank 1, a ring gear 5 connected around a crankshaft 3 of the engine 2 via a flywheel 4, and the ring It mainly comprises a starter 6 that cranks the engine 2 through the gear 6 and an ECU 7 that controls the operation of the engine 2.

  The engine 2 has four cylinders 10 including cylinders 9 in which pistons 8 connected to the crankshaft 3 reciprocate. The fuel stored in the fuel tank 1 is pumped to the common rail 14 through the flow control valve 13 provided in the fuel supply pipe 12 by the high-pressure pump 11 and accumulated in the common rail 14. The common rail pressure (fuel pressure) at this time is measured by a pressure sensor 15 attached to the common rail 14. The accumulated fuel is injected into the compressed air in each cylinder 10 through the injection nozzle 16 to burn and expand, thereby moving the piston 8 up and down. The drive shaft 17 of the high-pressure pump 11 is mechanically connected to the crankshaft 3 via a gear 18 or the like, and is driven in conjunction with the output of the engine 2.

  The starter 6 mainly includes a pinion 19 that can mesh with the ring gear 5 and a motor 20 that rotationally drives the pinion 19. The rotating shaft 21 of the motor 20 can be expanded and contracted toward the ring gear 5 by an actuator.

  The ECU 7 determines a target pressure of an appropriate common rail pressure according to the driving state of the vehicle, and controls the flow control valve 13 so that the detection value of the pressure sensor 15 becomes the target pressure. Then, an actuator (for example, a solenoid or a piezoelectric element) in the injection nozzle 16 is driven according to the control map to inject fuel into each cylinder 10. Moreover, when the stop request | requirement of the engine 2 generate | occur | produces, the fuel injection from the injection nozzle 16 is stopped. On the other hand, when a restart request for the engine 2 is generated, the motor 20 is activated to rotate the pinion 19, and the rotation shaft 21 is extended by the actuator so that the pinion 19 is engaged with the ring gear 5. Ranking. The engine 2 stop request is issued, for example, when some of items such as the vehicle speed (detected by the wheel speed sensor) and the battery voltage satisfy a predetermined condition. The restart request for the engine 2 is issued, for example, when a gear position, a clutch pedal state, or the like satisfies a predetermined condition.

  Further, the ECU 7 detects the rotational speed of the engine 2 by a rotation sensor 22 attached to the side surface of the flywheel 4 or the ring gear 5. As this rotation sensor 22, what detects the unevenness | corrugation carved in the surface of the flywheel 4 and the number of teeth of the ring gear 5 with a Hall element or an electromagnetic pick-up can be illustrated.

In the idling stop system having such a configuration, a method for controlling the idling stop of the internal combustion engine according to the embodiment of the present invention when an engine stop request is generated will be described below based on the flowchart shown in FIG. To do.

  First, when a stop request for the engine 2 is generated (S10), the flow control valve 13 is opened to increase the target pressure of the common rail pressure (fuel pressure) (S20). The increase value of the target pressure needs to exceed a normal target pressure at the time of restarting the engine 2 (for example, 30 MPa that is a target pressure at idling). The maximum allowable pressure of the common rail 14 (for example, 180 to 200 MPa) determined from the sealing performance of the high-pressure part of the system. Note that such maximum allowable pressure is practically set by setting the opening degree of the flow control valve 13 to about 100%.

  When a restart request for the engine 2 is generated (S30), the common rail pressure is compared with the minimum pressure Ps. When the common rail pressure is higher (S40), the common rail 14 is depressurized (S50). Then, the common rail pressure is reduced until it reaches the minimum pressure Ps (S60). The minimum pressure Ps is a pressure required for fuel to be injected from the injection nozzle 16 and burned in the cylinder 10. For example, a value of 30 MP or more which is the target pressure at the time of idling described above is used. it can. When the common rail pressure reaches the minimum pressure Ps, the engine 2 is cranked by the starter 6 and restarted (S70).

  An example of changes over time in the engine speed and the common rail pressure at this time is shown in FIG. The engine speed is based on a value detected by the rotation sensor 22.

  When a request to stop the engine 2 is generated, the ECU 7 sets the fuel injection amount to zero (FIG. 3B) and increases the target pressure of the common rail 14 to the maximum allowable pressure. As the target pressure increases, the discharge amount of the high-pressure pump 11 increases, and the common rail pressure increases from zero (FIG. 3C). Further, the engine rotation speed decreases due to the load applied to the crankshaft 3 due to the increase in the pumping amount of the high-pressure pump 11 (FIG. 3A).

  On the other hand, the common rail pressure does not actually reach the maximum allowable pressure due to the decrease in the discharge amount of the high-pressure pump 11 due to the decrease in the engine rotation speed, and the discharge amount and the amount of fuel leakage from the high-pressure pump 11 and the injection nozzle 16. A peak value is shown at the time when and are balanced, and thereafter it starts to decrease (FIG. 3 (c)).

  And when the restart request | requirement of the engine 2 generate | occur | produces, ECU7 will instruct | command pressure relief of the common rail 14 (FIG.3 (d)), and will start a pressure relief means. Since the common rail pressure is reduced by this pressure release means (FIG. 3C), fuel injection is started when the minimum pressure Ps is reached (FIG. 3B). As a result, since the fuel is combusted in the cylinder 10 from the first compression stroke when the engine 2 is restarted, the engine rotation speed increases rapidly (FIG. 3 (a)).

  In this way, the target pressure of the common rail pressure is increased when a stop request for the engine 2 is generated, and when the restart request is subsequently generated, the common rail 2 is depressurized and fuel is injected from the injection nozzle 16. In addition, by reducing the common rail pressure to the minimum pressure Ps, which is a pressure necessary for the fuel to burn in the cylinder 10, the fuel burns in the cylinder 10 from the first compression stroke when the engine 2 is restarted. In addition, since the combustion pressure rise does not become excessive, the engine 2 can be restarted more quickly than before without increasing the combustion noise at the time of restart.

  As the pressure release means of the common rail 14, there are a method using an existing injection nozzle 16 and a method using a new dedicated pressure release valve 23 as shown in FIG.

  In the former method using the injection nozzle 16, the actuator in the injection nozzle 16 is operated intermittently (in a pulsed manner) in such a short time that fuel is not injected into the cylinder 10 to operate the fuel pressure. Try to drain as oil.

  In the latter method using the pressure relief valve 23, a pressure relief valve 23 that can be electrically opened and closed by an actuator is installed on the common rail, and the pressure relief valve 23 is operated intermittently under the control of the ECU 7. To do.

  As the operation time of the actuator when the injection nozzle 16 is used, for example, as determined from FIG. 5, the minimum pulse width Pw (about 150 to 550 microseconds) at which the fuel injection amount (fuel leakage amount) becomes zero is obtained. It is preferably exemplified. However, in consideration of variations among the plurality of injection nozzles 16, it is preferable to multiply the minimum pulse width Pw by a correction coefficient k (for example, 0.5). In addition, as for the operation frequency of the actuator, in a four-cylinder 10 engine as shown in FIG. 1 or FIG. 4, it is set every crank angle less than 180 ° (eg every 10 °) or every fixed time (eg every 10 milliseconds) Is good.

FIG. 6 shows a method of controlling the idling stop of the internal combustion engine according to the reference example of the present invention. In the embodiment of the present invention shown in FIG. 2 described above, the burden on the injection nozzle 16 increases when the common rail 14 is depressurized, the service life is shortened, and the cost for newly installing the depressurization valve 23 increases. there's a possibility that. Therefore, in the onset Ming reference example, with the engine is restarted 2 (S40), and controls in accordance with the map for different high-pressure fuel injection from that of the normal control map of fuel injection from the injection nozzle 16 (S50) so I have to. This high-pressure fuel injection map performs control advantageous for reducing combustion noise, and describes, for example, the control contents for delaying the injection timing or dividing the injection. An example of a map for high-pressure fuel injection is shown in FIG. In this example, a correction amount for delaying the injection timing is defined in accordance with the common rail pressure with respect to a normal control map as a base. Thus, by appropriately delaying the injection timing, it is possible to suppress an increase in combustion pressure and prevent an increase in combustion noise.

1 Fuel tank 2 Engine 3 Crankshaft 4 Flywheel 5 Ring gear 6 Starter 7 ECU
8 Piston 9 Cylinder 10 Cylinder 11 High pressure pump 12 Fuel supply pipe 13 Flow rate control valve 14 Common rail 15 Pressure sensor 16 Injection nozzle 17 Drive shaft 18 Gear 19 Pinion 20 Motor 21 Rotating shaft 22 Rotation sensor 23 Pressure release valve

Claims (3)

The internal combustion engine is equipped with a common rail system that stores fuel that has been boosted to the target pressure with a high-pressure pump that rotates in conjunction with the crankshaft of the engine, and injects the stored fuel into the cylinder through the injection nozzle. A control method,
When the engine stop request occurs, the target pressure is increased to the maximum allowable pressure of the common rail system ,
Thereafter, when a restart request occurs, the pressure of the common rail is compared with the minimum pressure Ps necessary for fuel to be injected from the injection nozzle and burned in the cylinder,
When the common rail pressure is higher, the common rail pressure is reduced to the minimum pressure Ps, and then the engine is restarted. The common rail pressure is reduced to the minimum pressure Ps by instantaneously and intermittently opening and closing the actuator in the injection nozzle so that the fuel does not inject into the cylinder, and then the engine is restarted. The idling stop control method for an internal combustion engine according to claim 1 . A pressure relief valve is provided in the common rail, and the engine is restarted after the common rail pressure is lowered to the lowest pressure Ps by intermittently opening and closing the pressure relief valve. The idling stop control method for an internal combustion engine according to claim 1 .

Images