JP7826871B2 - Fuel injection system for internal combustion engines - Google Patents

Description

This disclosure relates to a fuel injection system for an internal combustion engine.

Patent Document 1 discloses a fuel injection system for an internal combustion engine that includes a port injection valve that injects fuel into an intake port and an in-cylinder injection valve that injects fuel into a combustion chamber, and that injects fuel from the port injection valve when the engine is cold.

JP 2014-234730 A

In the fuel injection device for an internal combustion engine disclosed in Patent Document 1, when the internal combustion engine is operating with fuel injected from the port injection valve, the nose of the in-cylinder injection valve is heated by the heat from fuel combustion, and the fuel filled in the nose may rise in temperature and become very hot. When the fuel filled in the nose becomes very hot, the fuel density in the nose decreases and vapor is generated. In this case, if fuel injection is switched from a port injection mode in which the internal combustion engine is driven by fuel injection from the port injection valve to an in-cylinder injection mode in which the internal combustion engine is driven by fuel injection from at least the in-cylinder injection valve, there is a risk of the internal combustion engine misfire due to the decrease in fuel density and the generation of vapor.

In view of the above, at least one embodiment of the present invention aims to provide a fuel injection system for an internal combustion engine that can prevent misfires in the internal combustion engine even when switching from port injection mode to direct injection mode while the internal combustion engine is operating.

(1) A fuel injection system for an internal combustion engine according to at least one embodiment of the present invention comprises a port injection valve for injecting fuel into an intake port provided in the internal combustion engine, an in-cylinder injection valve for injecting fuel into a combustion chamber provided in the internal combustion engine, and a control device for controlling the port injection valve and the in-cylinder injection valve, wherein when switching from a port injection mode in which the internal combustion engine is driven by fuel injection from the port injection valve to an in-cylinder injection mode in which the internal combustion engine is driven by fuel injection from at least the in-cylinder injection valve, the control device switches from the port injection mode to a throw-away injection mode, and in the throw-away injection mode, the port injection valve injects the fuel and the in-cylinder injection valve injects the fuel at a timing that does not contribute to combustion in the internal combustion engine, until the internal combustion engine completes a predetermined period, and when the predetermined period ends and the throw-away injection is completed, the control device switches to the in-cylinder injection mode.

According to the configuration (1) above, when switching from port injection mode to direct injection mode, the control device injects fuel from the port injection valve and performs a throw-off injection, in which fuel is injected from the direct injection valve at a timing that does not contribute to combustion in the internal combustion engine, until the end of a predetermined period of time, and then switches to direct injection mode after the throw-off injection. This makes it possible to prevent misfires in the internal combustion engine even when fuel injection is switched from port injection mode to direct injection mode while the internal combustion engine is operating.

(2) In some embodiments, in the configuration described in (1) above, when the temperature of the internal combustion engine is below a predetermined temperature, the timing at which the exhaust gas does not contribute to the combustion of the fuel is the exhaust stroke of the internal combustion engine, and when the temperature of the internal combustion engine is equal to or higher than the predetermined temperature, the timing at which the exhaust gas does not contribute to the combustion of the fuel is the latter part of the combustion stroke of the internal combustion engine.

According to the configuration (2) above, when the temperature of the internal combustion engine is below a predetermined temperature, fuel is injected from the in-cylinder injection valve during the exhaust stroke of the internal combustion engine, so that the fuel burns downstream of the internal combustion engine and activates the exhaust purification device (catalyst). When the temperature of the internal combustion engine is above a predetermined temperature, fuel is injected from the in-cylinder injection valve later in the combustion stroke of the internal combustion engine, so that the exhaust purification device (catalyst) located downstream of the internal combustion engine is prevented from becoming too hot and damage to the catalyst is prevented.

(3) In some embodiments, in the configuration described in (1) or (2) above, the port injection valve injects fuel so as to achieve a corrected air-fuel ratio obtained by correcting the target air-fuel ratio required for the internal combustion engine to the lean side until the end of the predetermined period.

According to the configuration (3) above, the port injection valve injects fuel so that the target air-fuel ratio required by the internal combustion engine is corrected to the lean side until the internal combustion engine has completed a predetermined period of time. This allows oxygen to be stored in the exhaust purification device (catalyst), allowing the fuel (HC) injected by the waste injection to be treated (oxidized).

(4) In some embodiments, in the configuration described in (1) or (2) above, when the internal combustion engine is operating at a low load, the port injection valve injects fuel until the end of the predetermined period so as to achieve a corrected air-fuel ratio obtained by correcting the target air-fuel ratio required by the internal combustion engine to the lean side, and when the internal combustion engine is operating at a high load, the port injection valve injects fuel until the end of the predetermined period so as to achieve the target air-fuel ratio required by the internal combustion engine.

According to the configuration (4) above, when the internal combustion engine is operating at low load, the port injection valve injects fuel to achieve a corrected air-fuel ratio that is a leaner correction of the target air-fuel ratio required by the internal combustion engine until the end of a predetermined period. This allows oxygen to be stored in the exhaust purification device (catalyst) and the fuel (HC) injected by the waste injection can be processed (oxidized). Furthermore, when the internal combustion engine is operating at high load, the port injection valve injects fuel to achieve the target air-fuel ratio required by the internal combustion engine until the end of a predetermined period. This allows the internal combustion engine to maintain high load operation even when fuel injection is switched from port injection mode to direct injection mode while the internal combustion engine is operating.

At least one embodiment of the present invention makes it possible to prevent misfires in an internal combustion engine even when fuel injection is switched from port injection mode to direct injection mode while the internal combustion engine is operating.

1 is a diagram schematically illustrating an internal combustion engine according to an embodiment. 2 is a block diagram showing the port injection valve and the in-cylinder injection valve shown in FIG. 1 and a control device for controlling them. FIG. 3 is a time chart showing the operation of the port injection valve and the in-cylinder injection valve controlled by the control device shown in FIG. 2, and showing the operation when fuel injection is switched from the port injection valve to the in-cylinder injection valve during operation of the internal combustion engine.

Embodiments will be described below with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described in the embodiments or shown in the drawings are not intended to limit the scope of the present invention and are merely illustrative examples.

Figure 1 is a diagram showing a schematic diagram of an internal combustion engine according to an embodiment. Figure 2 is a diagram showing the port injection valve and in-cylinder injection valve shown in Figure 1, as well as a control device that controls them. Figure 3 is a time chart showing the operation of the port injection valve and in-cylinder injection valve controlled by the control device shown in Figure 2, and is a time chart showing the operation when fuel injection is switched from the port injection valve to the in-cylinder injection valve while the internal combustion engine is operating.

As shown in FIG. 1, the internal combustion engine 1 according to the embodiment includes a cylinder block 10 and a cylinder head 12. The cylinder block 10 includes a cylinder 16 in which a piston 14 reciprocates, and a cylinder head 12 is fixed to the cylinder block 10. The cylinder head 12 includes a spark plug 18, and a combustion chamber 20 is formed between the cylinder head 12 and the piston 14. The cylinder head 12 includes an intake port 22 and an exhaust port 24. An exhaust pipe is connected to the exhaust port 24, and an exhaust purification device is provided in the exhaust pipe. The exhaust purification device may be, for example, a three-way catalyst. For example, two intake ports 22 and two exhaust ports 24 are provided for each combustion chamber 20, but this is not limited to this. The intake port 22 includes an intake valve 26 that opens and closes the intake port 22, and the exhaust port 24 includes an exhaust valve 28 that opens and closes the exhaust port 24. The intake port 22 includes a port injection valve 30 for injecting fuel into the intake port 22. Additionally, the cylinder block 10 or cylinder head 12 is provided with an in-cylinder injection valve 32 for injecting fuel into the combustion chamber 20. These port injection valves 30 and in-cylinder injection valves 32 are controlled by a control device 34, as shown in FIG. 2.

The control device 34 is composed of a processor (not shown) consisting of an arithmetic unit, registers for storing instructions and information, and peripheral circuits, memory (not shown) such as ROM (Read Only Memory) and RAM (Random Access Memory), and an input interface (not shown).

The control device 34 can switch between a mode in which the internal combustion engine 1 is driven by fuel injection from the port injection valve 30 (hereinafter referred to as the "port injection mode") and a mode in which the internal combustion engine 1 is driven by fuel injection from at least the in-cylinder injection valve 32 (hereinafter referred to as the "in-cylinder injection mode"). The in-cylinder injection mode may be one in which the internal combustion engine 1 is driven by fuel injection from both the in-cylinder injection valve 32 and the port injection valve 30, as long as the internal combustion engine 1 is driven by fuel injection from at least the in-cylinder injection valve 32, or one in which the internal combustion engine 1 is driven by fuel injection from only the in-cylinder injection valve 32.

As shown in FIG. 3 , when switching from port injection mode to in-cylinder injection mode, the control device 34 injects fuel from the port injection valve 30 and performs a throw-in injection, in which fuel is injected from the in-cylinder injection valve 32 at a timing that does not contribute to combustion in the internal combustion engine 1, until the end of a predetermined period of time in the internal combustion engine 1. After the throw-in injection, the control device 34 switches to in-cylinder injection mode. Note that the throw-in injection, in which fuel is injected from the in-cylinder injection valve 32 at a timing that does not contribute to combustion in the internal combustion engine 1, is referred to as the throw-in injection mode. Microscopically, switching from port injection mode to in-cylinder injection mode can be visualized as switching between port injection mode, throw-in injection mode, and in-cylinder injection mode in that order. That is, when a command to switch to in-cylinder injection mode is issued during port injection mode, the control device switches to the throw-in injection mode, injects fuel from the port injection valve 30 to maintain engine operation, and injects fuel from the in-cylinder injection valve 32 at a timing that does not contribute to combustion in the internal combustion engine 1. After performing the waste injection mode for a predetermined period of time, the waste injection mode ends and the system transitions to in-cylinder injection mode, in which fuel is injected from the in-cylinder injection valve 32 at a timing that contributes to combustion in the internal combustion engine 1. Note that Figure 3 shows an example of the in-cylinder injection mode in which the internal combustion engine 1 is driven by fuel injection only from the in-cylinder injection valve 32.

Times that do not contribute to fuel combustion are times that are not converted into rotational torque of the internal combustion engine 1, such as times other than the intake stroke and compression stroke of the internal combustion engine 1.

The predetermined period can be set arbitrarily, but for example, it can be set in units of the number of cycles of the internal combustion engine 1. When the predetermined period is set in units of the number of cycles of the internal combustion engine 1, the predetermined period can be set to the time until the internal combustion engine 1 completes the predetermined number of cycles. The predetermined cycle can be set arbitrarily, and can be one cycle or several cycles, for example, two to three cycles.

The control device 34 injects fuel from the port injection valve 30 until the end of a predetermined period of time when the internal combustion engine 1 is in operation, so as to achieve a corrected air-fuel ratio obtained by correcting the target air-fuel ratio required by the internal combustion engine 1 to the lean side (lean side). As a result, the target air-fuel ratio for fuel injection from the port injection valve 30 in the discard injection mode is leaner than the target air-fuel ratio before switching from port injection mode to direct injection mode. In port injection mode and direct injection mode, the fuel injection amount is set to achieve the target air-fuel ratio set based on the vehicle's driving conditions, etc. When fuel is injected from the port injection valve 30 in the discard injection mode, the fuel injection amount is set to achieve a corrected air-fuel ratio obtained by correcting the target air-fuel ratio in the port injection mode immediately before switching to the discard injection mode to the lean side. For example, if the injection time from the port injection valve 30 before the switching command is set to t1 and the injection time after the switching command is set to t2, the air-fuel ratio after the switching command will be leaner than the air-fuel ratio before the switching command by setting the injection time before the switching command t1 to be greater than the injection time after the switching command t2.

However, when the internal combustion engine 1 is operating under high load, the target air-fuel ratio is not corrected to the lean side until the internal combustion engine 1 has completed a predetermined period of time, as described above, and fuel is injected from the port injection valve 30 so as to achieve the target air-fuel ratio required by the internal combustion engine 1. High load operation of the internal combustion engine 1 includes, for example, when the vehicle is traveling at high speeds (e.g., 60 km/h or more), when the vehicle is traveling in an uphill lane, or when the accelerator is depressed above a predetermined level.

Therefore, fuel is injected from the port injection valve 30 so as to achieve a corrected air-fuel ratio that is the target air-fuel ratio required by the internal combustion engine 1 corrected to the lean side only when the internal combustion engine 1 is operating at a low load (other than when it is operating at a high load). Examples of when the internal combustion engine 1 is operating at a low load include when the internal combustion engine 1 is idling or when the vehicle is operating at low speeds in urban areas.

It is preferable that the amount of fuel injected from the in-cylinder injection valve 32 when performing a waste injection be as small as possible. For example, the cycle of the internal combustion engine 1 in which fuel is injected from the in-cylinder injection valve 32 at a timing that does not contribute to fuel combustion is one cycle.

Fuel injected from the in-cylinder injection valve 32 at a timing that does not contribute to fuel combustion is the minimum amount that can be injected from the in-cylinder injection valve 32. The minimum amount that can be injected from the in-cylinder injection valve 32 is determined by the performance of the in-cylinder injection valve 32, and is the minimum amount within the range in which the fuel injection amount can be accurately controlled by the in-cylinder injection valve 32. The minimum amount that can be injected from the in-cylinder injection valve 32 may be determined by experiment, or may be determined by calculation from the diameter of the injection port of the in-cylinder injection valve 32, the fuel injection pressure of the in-cylinder injection valve 32, etc. Note that the specified period and fuel injection amount when performing a waste injection are not limited to those described above. For example, the specified period and fuel injection amount may be set so that all of the high-temperature fuel inside the in-cylinder injection valve 32 can be injected.

The timing of fuel injection from the in-cylinder injection valve 32 when performing a waste injection may be changed according to specified conditions. For example, when the temperature of the internal combustion engine 1 is below a predetermined temperature, the timing at which fuel is injected from the in-cylinder injection valve 32 and does not contribute to fuel combustion is the exhaust stroke of the internal combustion engine 1. When the temperature of the internal combustion engine 1 is equal to or higher than the predetermined temperature, the timing at which fuel is injected from the in-cylinder injection valve 32 and does not contribute to fuel combustion is the latter part of the combustion stroke of the internal combustion engine 1.

For example, the predetermined temperature is the temperature at which a catalyst built into an exhaust purification device located downstream of the exhaust port 24 becomes activated. Therefore, for example, if the temperature of the internal combustion engine 1 is below the temperature at which the catalyst becomes activated, fuel is injected from the in-cylinder injection valve 32 during the exhaust stroke of the internal combustion engine 1; if the temperature is above the temperature at which the catalyst becomes activated, fuel is injected from the in-cylinder injection valve 32 during the latter part of the combustion stroke of the internal combustion engine 1.

According to the fuel injection system for the internal combustion engine 1 according to the embodiment described above, when switching from port injection mode to in-cylinder injection mode, the control device 34 injects fuel from the port injection valve 30 and performs a throw-off injection, in which fuel is injected from the in-cylinder injection valve 32 at a timing that does not contribute to combustion in the internal combustion engine 1, until the end of a predetermined period of time in the internal combustion engine 1, and then switches to in-cylinder injection mode after the throw-off injection. This allows high-temperature fuel to be discharged from the in-cylinder injection valve 32 when fuel injection is switched from port injection mode to in-cylinder injection mode while the internal combustion engine 1 is operating, thereby preventing misfires in the internal combustion engine 1. At this time, fuel can be discharged from the in-cylinder injection valve 32 while injecting fuel from the port injection valve 30 to maintain operation of the internal combustion engine 1, without significantly affecting the operation of the internal combustion engine 1.

Furthermore, for example, the control device 34 causes the port injection valve 30 to inject fuel so as to achieve a corrected air-fuel ratio that is the target air-fuel ratio required by the internal combustion engine 1 corrected to the lean side until the internal combustion engine 1 has completed a predetermined period of time. This allows oxygen to be stored in the exhaust purification device (catalyst) and can process (oxidize) the fuel (HC) injected by the waste injection.

Furthermore, for example, when the internal combustion engine 1 is operating under high load, the control device 34 causes the port injection valve 30 to inject fuel so as to achieve the target air-fuel ratio required by the internal combustion engine 1 until the end of a predetermined period of time. Therefore, the high load operation of the internal combustion engine 1 can be maintained even when fuel injection is switched from port injection mode to direct injection mode while the internal combustion engine 1 is operating.

Furthermore, for example, the cycle of the internal combustion engine 1, in which fuel is injected from the in-cylinder injection valve 32 at a timing that does not contribute to fuel combustion, is one cycle, so the amount of fuel wasted from the in-cylinder injection valve 32 can be reduced.

Furthermore, for example, when the temperature of the internal combustion engine 1 is below a predetermined temperature, fuel is injected from the in-cylinder injection valve 32 during the exhaust stroke of the internal combustion engine 1, so that the fuel burns downstream of the internal combustion engine and activates the exhaust purification device (catalyst). Furthermore, for example, when the temperature of the internal combustion engine 1 is above a predetermined temperature, fuel is injected from the in-cylinder injection valve 32 during the latter part of the combustion stroke of the internal combustion engine 1, so that the exhaust purification device (catalyst) located downstream of the internal combustion engine 1 is prevented from becoming too hot and damage to the catalyst is prevented.

REFERENCE SIGNS LIST 1 Internal combustion engine 10 Cylinder block 12 Cylinder head 14 Piston 16 Cylinder 18 Spark plug 20 Combustion chamber 22 Intake port 24 Exhaust port 26 Intake valve 28 Exhaust valve 30 Port injection valve 32 In-cylinder injection valve 34 Control device

Claims (4)

a port injection valve for injecting fuel into an intake port provided in the internal combustion engine;
an in-cylinder injection valve provided in the internal combustion engine for injecting fuel into a combustion chamber;
a control device for controlling the port injection valve and the in-cylinder injection valve,
The control device
When switching from a port injection mode in which the internal combustion engine is driven by fuel injection from the port injection valve to an in-cylinder injection mode in which the internal combustion engine is driven by fuel injection from at least the in-cylinder injection valve,
switching from the port injection mode to a throw-away injection mode, in which the fuel is injected from the port injection valve and the fuel is injected from the direct injection valve at a timing that does not contribute to combustion in the internal combustion engine, until the internal combustion engine completes a predetermined period of time;
A fuel injection system for an internal combustion engine, which switches to the direct injection mode when the predetermined period ends and the waste injection ends . When the temperature of the internal combustion engine is lower than a predetermined temperature, the timing at which the combustion does not contribute to the combustion of the fuel is an exhaust stroke of the internal combustion engine,
When the temperature of the internal combustion engine is equal to or higher than the temperature, the timing at which the fuel does not contribute to combustion is a later stage of a combustion stroke of the internal combustion engine.
2. A fuel injection system for an internal combustion engine according to claim 1. the port injection valve injects fuel so as to achieve a corrected air-fuel ratio obtained by correcting a target air-fuel ratio required for the internal combustion engine to the lean side until the end of the predetermined period.
3. A fuel injection system for an internal combustion engine according to claim 1 or 2. During low load operation of the internal combustion engine, the port injection valve injects fuel until the end of the predetermined period so as to achieve a corrected air-fuel ratio obtained by correcting a target air-fuel ratio required for the internal combustion engine to the lean side,
During high load operation of the internal combustion engine, the port injection valve injects fuel so as to achieve a target air-fuel ratio required for the internal combustion engine until the end of the predetermined period.
3. A fuel injection system for an internal combustion engine according to claim 1 or 2.