JP6447823B2 - Fuel supply device - Google Patents

Description

  The present invention relates to a fuel supply device that supplies fuel to an addition valve that adds fuel to an exhaust passage of an internal combustion engine.

  Conventionally, an addition valve for adding fuel to the exhaust passage for the purpose of regeneration processing of a diesel particulate filter (DPF) provided in the exhaust passage of the internal combustion engine or reduction processing of NOx stored in the NOx storage reduction catalyst has been provided. A system provided is known (see, for example, Patent Document 1). In this type of system, fuel is boosted using a mechanical or electric feed pump, and fuel is added by supplying the boosted fuel to an addition valve. Patent Document 1 discloses a system in which fuel is supplied from a fuel supply pump as a feed pump to a fuel injection valve (addition valve).

JP 2010-203396 A

  By the way, it is necessary to add fuel to the addition valve at an optimum pressure according to the operation state of the internal combustion engine, the state of the exhaust gas, and the processing content in the aftertreatment device (DPF, NOx storage reduction catalyst, etc.). For example, in the reduction treatment of the NOx storage reduction catalyst, it is necessary to make a rich atmosphere in a short time, so it is preferable to add fuel at a high injection pressure. However, the conventional method of boosting the fuel supplied to the addition valve using a feed pump has a problem that it is difficult to add fuel in a wide pressure range because there is a limit to the pressure that can be boosted.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a fuel supply device that supplies fuel to an addition valve that can perform fuel addition in a wide pressure range.

(First invention)
In order to solve the above problems, a fuel supply device according to a first aspect of the present invention provides:
A fuel is supplied from a common rail that stores high-pressure fuel supplied to an injector that injects fuel into a cylinder of the internal combustion engine, and a reservoir that stores the fuel;
Adjusting means for adjusting the fuel pressure of the reservoir to a predetermined pressure level smaller than the fuel pressure of the common rail;
Supplying fuel in the reservoir to an addition valve for adding fuel to an exhaust passage of the internal combustion engine ;
The adjusting means includes
A pressure reducing valve provided on the common rail, for releasing the fuel of the common rail to the outside of the common rail when the valve is opened;
A sensor for detecting the pressure in the reservoir;
Control means for controlling opening and closing of the pressure reducing valve,
The reservoir stores fuel released from the pressure reducing valve,
The control means includes determination means for determining whether a detection value of the sensor satisfies the pressure level, and the pressure reducing valve so as to satisfy the pressure level when the detection value is less than the pressure level. It is characterized by opening .
(Second invention)
The fuel supply device according to the second invention is
A fuel is supplied from a common rail that stores high-pressure fuel supplied to an injector that injects fuel into a cylinder of the internal combustion engine, and a reservoir that stores the fuel;
Adjusting means for adjusting the fuel pressure of the reservoir to a predetermined pressure level smaller than the fuel pressure of the common rail;
Supplying fuel in the reservoir to an addition valve for adding fuel to an exhaust passage of the internal combustion engine;
The reservoir is provided in contact with the fuel in the reservoir, and has an expansion / contraction part that expands and contracts under the pressure of the fuel in the reservoir,
The expansion / contraction part is provided above the inlet and outlet of the reservoir provided separately, in the gravity direction.

  According to the present invention, the fuel from the common rail that stores the high-pressure fuel for in-cylinder injection is supplied to the reservoir, and the fuel in the reservoir is supplied to the addition valve. That is, fuel addition is performed using the common rail fuel through the reservoir. This makes it possible to add fuel at a higher injection pressure, that is, to add fuel in a wide pressure range as compared with the conventional method using fuel boosted by a pump. Further, the fuel pressure of the common rail is set for in-cylinder injection and is not preferably used as it is as the pressure of the fuel added to the exhaust passage. However, in the present invention, the fuel pressure of the reservoir is smaller than the fuel pressure of the common rail. Since the adjusting means for adjusting to a predetermined pressure level is provided, the fuel can be added to the exhaust passage at an appropriate pressure.

It is a block diagram of an engine system. It is the figure which illustrated the internal structure of the pressure-reduction valve. 3 is a flowchart of reservoir pressure control and addition valve fuel addition control executed by an ECU. It is a timing chart of each parameter relevant to the processing of FIG. It is the figure which showed the relationship between the volume elastic modulus of the fuel in a reservoir, the pressure difference in the reservoir before and after injection of the addition valve, and the reservoir volume. It is the figure which showed the example which enclosed gas in the reservoir | reserver. It is the figure which showed the example which enclosed the damper structure in the reservoir | reserver. It is the figure which showed the relationship between the damper function in a reservoir, an air mixing rate, and the volume elastic modulus of the fuel in a reservoir.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a configuration diagram of a common rail engine system 1 to which a fuel supply device of the present invention is applied. The engine system 1 includes a multi-cylinder diesel engine (hereinafter simply referred to as an engine) that is mounted on a vehicle and drives the vehicle, and controls the operation of the engine or exhausts exhausted from the engine. This system purifies gas. First, the configuration of the engine system 1 will be described.

  In the engine system 1, a fuel tank 4 that stores fuel to be injected into the cylinder of the engine, an electric feed pump 5 that pumps fuel from the fuel tank 4, and an electric pump drive driver 6 that drives the electric feed pump 5. Is provided. The fuel pumped up by the electric feed pump 5 is sent to the supply pump 9 through the pipe 7. A fuel filter 8 for removing foreign matters in the fuel is provided in the middle of the pipe 7. The pressure of the fuel passing through the pipe 7 is several hundred kPa, for example.

  A fuel pressure sensor 11 for detecting the pressure of the fuel is provided in the pipe 7 between the fuel filter 8 and the supply pump 9. The ECU 28 controls the rotation of the electric feed pump 5 so that the pressure detected by the fuel pressure sensor 11 becomes a predetermined pressure. In addition, when controlling the electric feed pump 5 by fixed rotation, the fuel pressure sensor 11 does not need to be provided.

  In the present embodiment, an example in which the feed pump 5 is provided at the position of the fuel tank 4 has been described. However, a feed pump may be provided in the supply pump 9 instead of or in addition to the feed pump 5. . In a system in which a feed pump is also provided in the supply pump 9, the pressure of the fuel pumped up by the electric feed pump 5 is increased by the feed pump in the supply pump 9. In this case, the electric feed pump 5 and the pipe 7 connected thereto function as a low pressure portion having a lower pressure than the feed pump in the supply pump 9 and the fuel in the common rail 2. Further, the feed pump in the supply pump 9 functions as an intermediate pressure unit that boosts the fuel at a pressure lower than the fuel pressure of the common rail 2. Further, the common rail 2 functions as a high-pressure portion that accumulates and holds high-pressure fuel.

  A return pipe 10 connected to the tank modules 4 and 5 is branched into a pipe 7 between the fuel filter 8 and the supply pump 9. The return pipe 10 is provided with a relief valve 12. The relief valve 12 is a check valve (check valve) that allows the flow of fluid in the direction from the pipe 7 to the tank modules 4 and 5 and prohibits the flow in the opposite direction. When the fuel in the pipe 7 is at a predetermined pressure or higher, the relief valve 12 is opened so that a part of the fuel flowing through the pipe 7 returns to the tank modules 4 and 5 via the return pipe 10.

  A supply pump 9 is provided downstream of the fuel filter 8. The supply pump 9 is a variable discharge high-pressure pump having a known structure. After the fuel supplied from the electric feed pump 5 through the fuel filter 8 is pressurized to the feed pressure by the built-in feed pump, the suction adjustment valve is used. To suck a predetermined amount into the plunger chamber, pressurize and discharge. The supply pump 9 may not include a feed pump. The supply pump 9 is driven using an engine crank as a power source. From the supply pump 9, high-pressure fuel pressurized to, for example, several tens of MPa to several hundreds of MPa is discharged. A return pipe 13 is connected to the supply pump 9. In the supply pump 9, cooling is performed by using a part of the supplied fuel, and the fuel used for cooling returns to the tank modules 4 and 5 via the return pipe 13.

  The high pressure fuel discharged from the supply pump 9 is supplied to the common rail 2 via the high pressure pipe 14. The common rail 2 accumulates (accumulates pressure) the high-pressure fuel supplied from the supply pump 9 while maintaining the pressure. The pressure accumulated in the common rail 2 corresponds to the fuel injection pressure of the injector 3. A fuel pressure sensor 15 that detects a fuel pressure (common rail pressure) accumulated in the common rail 2 is provided on one end side of the common rail 2.

  A pressure reducing valve 17 for reducing the common rail pressure is provided on the other end side of the common rail 2. FIG. 2 is a diagram illustrating the internal structure of the pressure reducing valve 17. As shown in FIG. 2, the pressure reducing valve 17 is an electromagnetic valve that is driven by, for example, a solenoid. Specifically, the pressure reducing valve 17 is provided so as to be slidable in the axial direction of the coil 18 inside the coil 18. A movable iron core 19, a spring 20 provided on one end side of the movable iron core 19 and energizing the movable iron core 19 in a direction in which the movable iron core 19 protrudes from the inside of the coil 18, and a fixed shape on the other end side of the movable iron core 19 And an opening / closing part 21 for opening / closing a return passage 2b formed in the common rail 2.

  When the coil 18 is not energized, the movable iron core 19 is urged by the spring 20 in a direction protruding from the coil 18, whereby the opening / closing part 21 closes (seal) the return passage 2 b, that is, the fuel storage space of the common rail 2. 2a and the return passage 2b are cut off. When the coil 18 is energized, the movable iron core 19 overcomes the urging force of the spring 20 by the electromagnetic force generated by the energization and is drawn inside the coil 18. With this pull-in, the opening / closing part 21 moves away from the position where the return passage 2b is closed (sealed), and the fuel accumulation space 2a and the return passage 2b are electrically connected. The fuel storage space 2a and the return passage 2b are connected via a small diameter portion 2c (orifice). The small diameter portion 2 c may be provided in the pressure reducing valve 17 or may be provided in the common rail 2. When the fuel storage space 2a and the return passage 2b are conducted, the fuel stored in the fuel storage space 2a is discharged to the outside of the common rail 2 through the return passage 2b. The discharge reduces the common rail pressure. Thus, the pressure is quickly reduced to the injection pressure corresponding to the vehicle running state, and the valve is opened when the fuel pressure in the common rail 2 becomes excessive, and also serves as a pressure limiter that releases the fuel at once.

  Returning to the description of FIG. 1, the high-pressure fuel accumulated in the common rail 2 is supplied to an injector 3 provided for each cylinder. That is, the common rail 2 (fuel accumulation space 2a) and each injector 3 are always connected by the pipe 29 in a conductive state.

  The injector 3 is a device for injecting fuel sent from the common rail 2 into the cylinder from an injection hole formed in the cylinder tip that is provided in the cylinder head constituting the upper part of the cylinder so that the tip is exposed in the cylinder. is there. The injector 3 has a known piezo-type or solenoid-type on-off valve structure. Specifically, an actuator (piezo actuator or solenoid actuator) is provided in the housing of the injector 3, and a nozzle body is provided on the front end side of the housing. A needle that is slidable in the axial direction (vertical direction) of the nozzle body is provided in the nozzle body. The space between the nozzle body and the needle is a flow passage through which fuel flows.

  When the actuator is not energized, the needle closes the tip of the nozzle body, and in this state, fuel is not injected. When the actuator is energized, a valve provided on the upper side of the needle opens, and fuel on the upper side of the needle flows into the return pipe 16 (see FIG. 1) via the valve. Along with this, the pressure on the upper side of the needle decreases, and the needle moves upward. Along with this movement, the tip of the nozzle body opens and fuel is injected from the tip. The fuel that has flowed into the return pipe 16 is returned to the tank modules 4 and 5.

  The fuel released from the common rail 2 when the pressure reducing valve 17 is opened is supplied to the reservoir 23. That is, the return passage 2b (see FIG. 2) formed in the common rail 2 and the reservoir 23 are connected by the pipe 22. The reservoir 23 is formed with an inlet 23 a connected to the pipe 22, and the inlet 23 a is electrically connected to the space in the reservoir 23. The reservoir 23 is a pressure accumulator that stores fuel released from the common rail 2. The reservoir 23 is provided with a check valve 24 (check valve) that adjusts the fuel pressure in the reservoir 23 to a predetermined maximum pressure or less. Further, the reservoir 23 is provided with a fuel pressure sensor 26 that detects the fuel pressure in the reservoir 23.

  The check valve 24 is provided so that the direction from the inner side to the outer side of the reservoir 23 is a forward direction in which circulation is permitted, and the direction from the outer side to the inner side is a reverse direction in which circulation is prohibited. The check valve 24 is connected to the tank modules 4 and 5 via a return pipe 25. The pressure at which the check valve 24 opens, that is, the maximum pressure that can be accumulated in the reservoir 23 is set to a pressure (for example, several MPa) smaller than the fuel pressure (several tens of MPa or more) of the common rail 2. When the pressure in the reservoir 23 exceeds the opening pressure of the check valve 24, the check valve 24 is opened, and a part of the fuel in the reservoir 23 is discharged out of the reservoir 23 through the check valve 24. Is done. As a result, the pressure in the reservoir 23 is reduced to a predetermined maximum pressure or less. The fuel released from the reservoir 23 is returned to the tank modules 4 and 5 via the return pipe 25.

  A purification unit for purifying exhaust gas is provided in the exhaust passage of the engine. The purification unit includes an oxidation catalyst that oxidizes and purifies HC and CO in the exhaust gas, a DPF that is provided downstream of the oxidation catalyst and collects PM in the exhaust gas, and a lean atmosphere that is provided downstream of the oxidation catalyst. And NOx storage reduction catalyst (LNT: Lean NOx Trap) for reducing and purifying NOx stored in a rich atmosphere. The oxidation catalyst and the DPF may be an integrated type, that is, a DPF with an oxidation catalyst. Further, instead of the NOx storage reduction catalyst, an SCR catalyst (SCR: Selective Catalytic Reduction) that selectively reduces NOx with urea may be provided.

  An addition valve 27 for adding fuel to the exhaust passage is provided in the exhaust passage upstream of the purification section. Fuel addition by the addition valve 27 is performed, for example, for a regeneration process in which PM collected in the DPF is burned and removed to regenerate the DPF, or a reduction process in which a rich atmosphere is created to reduce the NOx stored in the LNT. The The addition valve 27 has the same structure as the injector 3, that is, has a needle and an actuator that drives the needle, and the needle moves upward by the actuator, and fuel is injected from the tip of the nozzle along with the movement. To do.

  The fuel in the reservoir 23 is always supplied to the addition valve 27 via the pipe 31. That is, the reservoir 23 is formed with an outlet 23 b for letting out fuel in the reservoir 23. One end of the pipe 31 is connected to the outlet 23 b, and the other end of the pipe 31 is connected to the addition valve 27. ing. The fuel pressure in the addition valve 27, the piping 31, the reservoir 23, and the piping 22 is the same pressure (pressure in the reservoir 23).

  The engine system 1 is provided with an ECU 28 (Electronic Control Unit). The ECU 28 controls fuel injection (fuel injection amount, injection timing, injection pressure, etc.) by the injector 3 based on detection values of sensors (engine speed sensor, accelerator pedal sensor, etc.) provided in the engine system 1. Yes (controls engine operation). Further, the ECU 28 controls the rotation of the electric feed pump 5 (controls the electric pump driver 6) so that the pressure detected by the fuel pressure sensor 11 becomes a predetermined pressure. Further, the ECU 28 adjusts the discharge amount of high-pressure fuel discharged to the supply pump 9 so that the common rail pressure detected by the fuel pressure sensor 15 becomes a predetermined pressure, or drives the pressure reducing valve 17 to reduce the common rail pressure. .

  Further, the ECU 28 controls fuel addition by the addition valve 27 and controls the fuel pressure in the reservoir 23 by controlling driving of the pressure reducing valve 17 and the supply pump 9 in relation to the addition valve control. Hereinafter, the pressure control of the reservoir 23 and the fuel addition control of the addition valve 27 by the ECU 28 will be described in detail. FIG. 3 shows a flowchart of pressure control and fuel addition control executed by the ECU 28. FIG. 4 is a timing chart of each parameter related to the processing of FIG. 3, and shows the pressure of the reservoir 23, the drive of the addition valve 27, the flow rate of the supply pump 9, and the flow rate of the pressure reducing valve 17 from the top. . Further, (1) to (5) shown on the time axis of FIG. 4 correspond to the respective processes of FIG. 3, and specifically, (1) corresponds to the processes of S1 to S5. 2) corresponds to the process of S6, (3) corresponds to the processes of S6 and S7, (4) corresponds to the process of S8, and (5) corresponds to the end of the process of FIG. The process shown in FIG. 3 is started at the same time as the engine is started, for example, and thereafter repeatedly executed at a predetermined cycle.

  When the processing of FIG. 3 is started, the ECU 28 first determines whether or not the pressure of the reservoir 23 detected by the fuel pressure sensor 26 is less than a predetermined pressure (S1). This predetermined pressure may be changed according to the situation, or may be a predetermined constant value. 4 shows a line 101 for a predetermined pressure and a line 102 for the opening pressure of the check valve 24. The predetermined pressure of S1 is set to a value lower than the valve opening pressure of the check valve 24 (see FIG. 4).

  When changing the predetermined pressure of S1, for example, the ECU 28 operates the engine (for example, the engine speed, engine load (injection amount command value of the injector 3), etc.), exhaust gas state (exhaust temperature, exhaust flow rate). And a predetermined pressure is set based on what kind of processing is performed in the purification unit. For example, since the fuel injected from the addition valve 27 is difficult to evaporate when the exhaust temperature is low, the fuel is evaporated by increasing the minimum pressure (predetermined pressure) of the reservoir 23 and increasing the injection pressure of the addition valve 27. It can be done easily. In addition, for example, when the NOx reduction process is performed in the LNT as the purification unit, it is necessary to make the atmosphere rich in a short time, so the minimum pressure (predetermined pressure) of the reservoir 23 is increased and the injection of the addition valve 27 is performed. Increase the rate (injection amount per unit time).

  When the pressure in the reservoir 23 is equal to or higher than the predetermined pressure (S1: No), it is not necessary to increase the pressure in the reservoir 23, and the process proceeds to S7. On the other hand, when the pressure in the reservoir 23 is less than the predetermined pressure (S1: Yes), the pressure in the reservoir 23 is increased by the processes in S2 to S6. FIG. 4 shows an example in which the pressure in the reservoir 23 is less than a predetermined pressure.

  In increasing the pressure of the reservoir 23, first, the target pressure of the reservoir 23 (target injection pressure of the addition valve 27) is set, and the pressure difference between the target pressure and the detected value of the fuel pressure sensor 26 (pressure of the reservoir 23). ΔP is calculated (S2). Here, when a predetermined pressure corresponding to the situation is set in S1, the predetermined pressure is set as the target pressure in S2. When the predetermined pressure in S1 is a constant value, in S2, the target pressure is set based on, for example, the operating state of the engine, the state of exhaust gas, and what kind of processing is performed in the purification unit. In this embodiment, the example in which the target pressure is changed according to the situation has been described. However, the target pressure may be a predetermined constant value.

Next, based on the pressure difference ΔP and Equation 1 shown below, the amount of fuel required to increase the pressure in the reservoir 23 by the pressure difference ΔP obtained in S2 (the required pressure increase amount) is calculated (S3). ). Expression 1 is an expression obtained from a known relational expression (P = E · ΔV / V) between the pressure P and the strain (ΔV / V). In Expression 1, ΔV indicates the volume change amount of the fuel in the reservoir 23, that is, the boosting required amount. V indicates the volume of the fuel in the reservoir 23, and E indicates the volume elastic modulus of the fuel in the reservoir 23. ΔP indicates the pressure change amount of the fuel in the reservoir 23, that is, the pressure difference obtained in S2. The bulk modulus is obtained by dividing the increased pressure by the volume reduction ratio accompanying the pressure applied to the object, and is the reciprocal of the compressibility.
ΔV = V × ΔP / E (Formula 1)

  Equation 1 means that when the pressure in the reservoir 23 is increased by ΔP, the fuel volume decreases by ΔV. This means that the pressure is increased by ΔP by supplying fuel to the reservoir 23 by ΔV and forcibly reducing the volume of the fuel before the supply by ΔV.

  The volume V in Equation 1 may be a value determined in advance as the volume of the reservoir 23. ΔP may be the value obtained in S2. The bulk modulus tends to increase as the pressure increases. Therefore, the relationship between the bulk modulus and the pressure in the reservoir 23 is examined in advance and stored in the memory in the ECU 28, and the bulk modulus E corresponding to the detected value of the fuel pressure sensor 26 is obtained from the relationship. The bulk modulus E may be a predetermined constant value.

  After obtaining the pressure increase required amount ΔV from the equation 1, next, based on the pressure increase required amount ΔV, the amount of fuel to be discharged from the common rail 2 via the pressure reducing valve 17 (pressure reduction flow rate) is calculated (S4). Here, the required pressure increase ΔV obtained in S3 is set as the reduced pressure flow as it is.

  Next, the fuel discharge amount (pump discharge amount) of the supply pump 9 is calculated based on the required pressure increase ΔV (pressure reduction flow rate) (S5). Specifically, the discharge amount that cancels the decrease in the common rail pressure when the required pressure increase ΔV is released from the common rail 2 to the discharge amount determined by the injection of the injector 3 (the discharge amount that compensates the injection of the injector 3), that is, The pump discharge amount is calculated by adding the required pressure increase ΔV.

  Next, the pressure reducing valve 17 and the supply pump 9 are driven to increase the pressure of the reservoir 23 (S6). Specifically, the pressure reducing valve 17 is opened by energization of the coil 18 (see FIG. 2), and the fuel corresponding to the pressure reducing flow rate obtained in S4 is released (released) from the common rail 2 (time in FIG. 4). (Refer to the figure of the pressure reducing valve flow rate in (2)). At this time, since the common rail pressure is higher than the pressure of the reservoir 23, fuel can flow from the common rail 2 toward the reservoir 23, and fuel corresponding to the reduced pressure flow rate is introduced into the reservoir 23. Can do. By introducing this fuel, the pressure of the reservoir 23 can be increased to a predetermined pressure or more as shown by the time of (2) in FIG. Also, if the valve opening pressure of the check valve 24 is exceeded (when overshooting), the check valve 24 immediately opens, so that as shown in the time (2) of FIG. The pressure can be suppressed below a predetermined maximum pressure defined by the check valve 24 (the valve opening pressure of the check valve 24).

  Note that the amount of fuel discharged from the pressure reducing valve 17 per unit time varies depending on the common rail pressure. Therefore, the relationship between the common rail pressure and the fuel amount per unit time released from the pressure reducing valve 17 is stored in a memory in the ECU 28. In S6, the amount of fuel discharged from the pressure reducing valve 17 per unit time is obtained from the relationship and the current common rail pressure. The opening time of the pressure reducing valve 17 is set from the fuel amount per unit time and the pressure reducing flow rate obtained in S4.

  Further, in S6, the fuel corresponding to the pump discharge amount obtained in S5 is discharged from the supply pump 9 (see the supply pump flow rate at time (2) in FIG. 4). As a result, the common rail pressure can be kept at a predetermined pressure while suppressing the common rail pressure from being reduced.

  The supply pump 9 uses the engine crank as a power source. However, when the pressure of the reservoir 23 cannot be increased to a desired pressure by a single pressure increase process (processes S4 to S6), such as when the engine speed is low. The process of S4 to S6 may be executed by reducing the reduced pressure flow rate per one time or the pump discharge amount, and the process of S4 to S6 may be repeated until the pressure of the reservoir 23 is increased to a desired pressure. .

  In S6, the pressure reducing valve 17 may be driven based on the detected value while monitoring the detected value of the fuel pressure sensor 26. In this case, the calculation of the required pressure increase in S3 and the reduced flow rate in S4 can be omitted. Similarly, in S6, the supply pump 9 may be driven based on the detected value while monitoring the detected value of the fuel pressure sensor 15. In this case, it is possible to omit the calculation of the required pressure increase (the process of S3) and the calculation of the pump discharge amount according to the required pressure increase (the process of S6).

  Note that the ECU 28, the pressure reducing valve 17, and the check valve 24 that execute the processes of S1 to S6 correspond to the adjusting means of the present invention. The ECU 28 that executes the processes of S1 to S6 corresponds to the control means of the present invention. Further, the check valve 24 corresponds to the decompression means of the present invention. Further, the pressure between the lines 101 and 102 in FIG. 4 corresponds to the predetermined pressure level of the present invention.

  After increasing the pressure of the reservoir 23, or when the pressure of the reservoir 23 is originally equal to or higher than the predetermined pressure (S1: No), next, it is determined whether or not the addition valve 27 can add fuel (S7). Specifically, for example, when the amount of PM collected in the DPF is estimated from the differential pressure before and after the DPF and the amount of PM reaches a predetermined amount, it is assumed that the regeneration process of the DPF is necessary. The addition is judged as “OK”. On the other hand, when the PM amount is less than the predetermined amount, it is determined that the fuel addition is “NO” because it is not necessary to perform the DPF regeneration process yet. Further, for example, when the NOx purification rate of the LNT is estimated from the NOx amounts before and after the LNT and the NOx purification rate falls below a predetermined value, it is necessary to reduce the NOx stored in the LNT. It is determined that fuel addition is possible. On the other hand, when the NOx purification rate exceeds the predetermined value, it is determined that the reduction process is not yet required, and the fuel addition is determined as “No”.

  When it is determined that the fuel addition is “NO” (S7: No), the process of FIG. 3 is terminated. When it is determined that fuel addition is “permitted” (S7: Yes), as shown by time (4) in FIG. 4, the addition valve 27 is driven to add fuel to the exhaust passage (S8). . Thus, DPF regeneration processing and LNT reduction processing can be performed. As the fuel volume in the reservoir 23 decreases due to the addition of fuel by the addition valve 27, the pressure in the reservoir 23 decreases as shown in FIG. 4, but the next processing in FIG. The pressure is increased to the pressure between the lines 101 and 102. After the process of S8, the process of FIG.

  As described above, according to the present embodiment, the fuel released from the pressure reducing valve 17 of the common rail 2 is accumulated in the reservoir 23 at a pressure level different from the common rail pressure, and the accumulated fuel is supplied to the addition valve 27. To do. Therefore, it is possible to add fuel at a higher pressure than the configuration in which fuel is supplied from the feed pump built in the electric feed pump 5 or the supply pump 9 to the addition valve, and fuel can be added in a wider pressure range. Become. By raising the valve opening pressure of the check valve 24 to a pressure close to the common rail pressure, in principle, the reservoir 23 can store pressure up to a pressure close to the common rail pressure. Further, by adjusting the pressure reducing flow rate of the pressure reducing valve 17, the pressure of the reservoir 23 can be maintained at an arbitrary pressure with the valve opening pressure of the check valve 24 being the upper limit. As described above, fuel can be added in a wide range of pressure, so that the injection pressure of the addition valve 27 can be increased, for example. By making the pressure high, for example, in the reduction treatment of LNT, a rich atmosphere can be obtained in a short time.

  In addition, since the fuel is supplied to the reservoir 23 only when the pressure reducing valve 17 is driven, the amount of fuel returned from the reservoir 23 to the tank modules 4 and 5 via the check valve 24 can be suppressed, that is, to the reservoir 23. The wasteful fuel supply can be suppressed. Further, since the reservoir 23 is provided with the check valve 24, the pressure of the reservoir 23 can be prevented from becoming too high.

  In addition, since the pressure of the common rail 2 is less affected by the engine speed, even when the engine speed is low, the reservoir 23 can quickly accumulate a desired pressure level, and the addition valve 27 can receive fuel at a desired pressure level. Can be supplied quickly. On the other hand, in the configuration in which the fuel in the addition valve 27 is boosted using a feed pump built in the supply pump 9, it is difficult to supply high pressure to the addition valve 27 when the engine speed is low.

  In addition, this invention is not limited to the said embodiment, A various change is possible to the limit which does not deviate from description of a claim. Hereinafter, modifications of the present invention will be described.

(Modification 1)
In the engine system 1 of FIG. 1, when the injection amount of the addition valve 27 is large, the pressure of the reservoir 23 is significantly reduced, and the fuel spray injected from the addition valve 27 is deteriorated due to the significant decrease of the pressure of the reservoir 23 (fuel The diameter of the liquid droplets becomes large), and there is a concern that the performance may deteriorate due to the deterioration of fuel spray. In order to suppress the deterioration of the fuel spray, the injection pressure of the addition valve 27 (the pressure of the reservoir 23 at the time of injection) needs to be equal to or higher than a predetermined minimum pressure (for example, 0.5 MPa). Further, it is necessary to set the volume of the reservoir 23 so that the pressure drop of the reservoir 23 is suppressed so as not to fall below a predetermined minimum pressure when the addition valve 27 is injected. If the volume of the reservoir 23 is increased, the pressure drop of the reservoir 23 can be suppressed, but there is a limit to increasing the volume of the reservoir 23 in consideration of being mounted on a vehicle.

Therefore, here, it is considered to suppress the pressure drop of the reservoir 23 at the time of injection even when the volume of the reservoir 23 is small. When the above formula 1 is transformed into a formula for the volume V, the following formula 2 is obtained. In Equation 2, ΔP means the pressure difference before and after injection as shown in the reservoir pressure diagram of FIG. Further, ΔV means the volume change amount (volume reduction amount) of the fuel in the reservoir 23 due to the fuel injection of the addition valve 27. E means the bulk modulus of fuel in the reservoir 23, and V means the volume of the reservoir 23.
V = (E × ΔV) / ΔP (Expression 2)

  From Equation 2, in order to reduce the volume of the reservoir 23, (1) the volume elastic modulus E is reduced, (2) the volume change amount ΔV (the injection amount of the addition valve 27) is reduced, (3) the pressure difference Three methods of increasing ΔP are conceivable. Among them, the method (2) cannot be performed because if the injection amount of the addition valve 27 is decreased, the regeneration of the DPF and the reduction of NOx are hindered. As described above, as shown in FIG. 5, the smaller the volume elastic modulus E of the fuel in the reservoir 23 or the greater the pressure difference ΔP before and after the injection, the higher the design requirement that the predetermined minimum pressure is maintained during the injection. The volume of the reservoir 23 can be reduced. Regarding the pressure difference ΔP, the pressure difference ΔP can be reduced by increasing the pressure of the reservoir 23 at the start of injection.

  Hereinafter, a method for reducing the bulk modulus of the fuel in the reservoir 23 will be described. By placing an object (elastic body such as gas or rubber, damper structure, etc.) with a small volume elastic modulus into an object with a large volume elastic modulus (fixed, liquid, etc.) in the same space, the volume of the object with a large volume elastic modulus The elastic modulus can be greatly reduced. That is, as shown in FIG. 6 and FIG. 7, by enclosing a gas 30 or a damper structure 32 having a volumetric modulus smaller than that of the fuel in a space (in the fuel) in the reservoir 23 in contact with the fuel. The bulk modulus of fuel can be lowered.

  In the example of FIG. 6, before the injection of the addition valve 27, the gas 30 is deformed into a contracted state 30 a due to the pressure of the fuel in the reservoir 23. At the time of injection of the addition valve 27, the volume of fuel in the reservoir 23 is reduced by the amount of injection, and the gas 30 is deformed into an expanded state 30b (expanded state) so as to follow the decrease. Due to the elongation deformation of the gas 30, it is possible to suppress a pressure drop due to a change in the volume of the fuel before and after the injection. That is, when the gas 30 is in the extended state 30b, the space occupied by the fuel in the reservoir 23 can be made smaller than before the injection, and the space can be reduced, so that a drop in fuel pressure can be suppressed.

  The gas 30 may be sealed in the reservoir 23 in advance, or air may be supplied to the reservoir 23 together with fuel so that the air is held in the reservoir 23 and the held air may be used as the gas 30. . Note that air may be mixed into the reservoir 23 as the fuel is supplied to the reservoir 23. Therefore, the mixed air may be held in the reservoir 23, or when the air is not mixed or when the mixing amount is small. May intentionally supply air to the reservoir 23.

  In order to hold the air supplied to the reservoir 23 in the reservoir 23, for example, as shown in FIG. 6, the outlet 23 b of the reservoir 23 is provided above the inlet 23 a in the gravity direction, and the upper portion of the reservoir 23 (gravity direction). A holding space for the air supplied to the reservoir 23 is provided. An outlet 23b is provided below the holding space in the gravity direction. According to this, the fuel accumulates from the lower side in the reservoir 23, whereas the air is lighter than the fuel, and therefore proceeds to the upper side of the fuel and accumulates in the holding space above the reservoir 23. Since the outlet 23b is provided below the holding space, the air accumulated in the holding space can hardly flow out of the reservoir 23 from the outlet 23b.

  In the example of FIG. 6, the gas 30 may be a gas other than air, or an elastic body such as rubber may be enclosed in the reservoir 23 instead of the gas 30.

  In the example of FIG. 7, a damper structure 32 having a spring 33 and a movable plate 34 is provided in the reservoir 23. The movable plate 34 is provided at a position above the outlet 23b of the reservoir 23 so as to be movable up and down so as to close the space in which the fuel is accumulated. The spring 33 is provided on the back side (opposite to the fuel) of the movable plate 34 so as to urge the movable plate 34 downward.

  Before the injection of the addition valve 27, the damper structure 32 receives the fuel pressure in the reservoir 23 and the spring 33 is contracted. At the time of injection of the addition valve 27, the volume of the fuel in the reservoir 23 decreases by the amount of injection, and the damper structure 32 (spring 33) extends to follow the decrease, and the movable plate 34 moves downward ( Displacement in the direction of fuel compression). When the movable plate 34 is displaced in the direction in which the fuel is compressed, the space occupied by the fuel in the reservoir 23 can be made smaller than before injection, and the space can be reduced, so that a drop in fuel pressure can be suppressed.

  FIG. 8 shows how the bulk elastic modulus of the fuel in the reservoir 23 depends on the damper function (the damper capacity of the damper structure 32 in FIG. 7) and the air mixing rate (the amount of the gas 30 in FIG. 6). It is the figure which showed whether it changes. As shown in FIG. 8, the larger the damper function and the air mixing rate, the smaller the bulk modulus of the fuel. Since the volume elastic modulus of the fuel can be reduced, the pressure drop in the reservoir 23 before and after injection can be suppressed, and the volume of the reservoir 23 can be reduced (see FIG. 5). As described above, the gas 30 and the damper structure 32 function as an accumulator that accumulates pressure when the fuel pressure in the reservoir 23 is large and reduces the volume in the reservoir 23 based on the accumulated energy when the fuel pressure decreases. .

  The bulk modulus of elasticity of the gas 30 in FIG. 6 and the damper structure 32 (spring 33) in FIG. 7 may be any value as long as it is smaller than the bulk modulus of the fuel, but the smaller the value as shown in FIG. The volume of can be reduced. The gas 30 and the damper structure 32 correspond to the stretchable part of the present invention.

(Other variations)
In the above embodiment, the pressure of the reservoir 23 is adjusted by opening / closing the pressure reducing valve 17 of the common rail 2 and the check valve 24 of the reservoir 23, but the present invention is not limited to this. For example, the common rail 2 and the reservoir 23 may be always connected to each other without using the pressure reducing valve 17. According to this, fuel is always supplied from the common rail 2 to the reservoir 23, but since the check valve 24 is provided in the reservoir 23, the pressure of the reservoir 23 can be maintained below the valve opening pressure of the check valve 24.

  For example, instead of the check valve 24 having a fixed valve opening pressure, a pressure reducing valve that can be opened and closed by ECU control is provided in the reservoir, similar to the pressure reducing valve 17 of the common rail 2, and the pressure of the reservoir is reduced by the pressure reducing valve. May be adjusted. This also makes it possible to set the pressure of the reservoir to an arbitrary pressure. When the pressure reducing valve is provided in the reservoir, the common rail and the reservoir may be always connected to each other. Moreover, a pressure reducing valve or a check valve for adjusting the pressure in the pipe (corresponding to the pressure of the reservoir) may be provided in the pipe connecting the common rail and the reservoir. Further, a movable wall is provided in the reservoir so as to constitute a part of the peripheral wall of the fuel accumulation space, and the position of the movable wall is controlled to change the volume of the fuel accumulation space, thereby reducing the pressure of the reservoir. You may adjust it.

2 Common rail 3 Injector 17 Pressure reducing valve 23 Reservoir 24 Check valve 27 Addition valve 28 ECU

Claims (11)

A reservoir (23) for storing fuel by supplying fuel from a common rail (2) for storing high-pressure fuel to be supplied to an injector (3) for injecting fuel into a cylinder of an internal combustion engine;
Adjusting means (17, 24, 26, 28, S1 to S6) for adjusting the fuel pressure of the reservoir to a predetermined pressure level smaller than the fuel pressure of the common rail;
Supplying fuel in the reservoir to an addition valve (27) for adding fuel to an exhaust passage of the internal combustion engine ;
The adjusting means includes
A pressure reducing valve (17) provided on the common rail, for releasing the fuel of the common rail to the outside of the common rail when the valve is opened;
A sensor (26) for detecting the pressure in the reservoir;
Control means (28, S1 to S6) for controlling the opening and closing of the pressure reducing valve,
The reservoir stores fuel released from the pressure reducing valve,
The control means includes determination means (S1) for determining whether or not a detection value of the sensor satisfies the pressure level, and satisfies the pressure level when the detection value is less than the pressure level. A fuel supply device that opens the pressure reducing valve .   A reservoir (23) for storing fuel by supplying fuel from a common rail (2) for storing high-pressure fuel to be supplied to an injector (3) for injecting fuel into a cylinder of an internal combustion engine;
  Adjusting means (17, 24, 26, 28, S1 to S6) for adjusting the fuel pressure of the reservoir to a predetermined pressure level smaller than the fuel pressure of the common rail;
  Supplying fuel in the reservoir to an addition valve (27) for adding fuel to an exhaust passage of the internal combustion engine;
  The reservoir is provided in contact with the fuel in the reservoir, and has an expansion / contraction portion (30, 32) that expands and contracts under the pressure of the fuel in the reservoir,
  The fuel supply device according to claim 1, wherein the expansion / contraction part is provided above the inlet (23a) and the outlet (23b) of the reservoir provided separately.   The adjusting means includes
  A pressure reducing valve (17) provided on the common rail, for releasing the fuel of the common rail to the outside of the common rail when the valve is opened;
  A sensor (26) for detecting the pressure in the reservoir;
  Control means (28, S1 to S6) for controlling the opening and closing of the pressure reducing valve,
  The reservoir stores fuel released from the pressure reducing valve,
  The control means includes determination means (S1) for determining whether or not a detection value of the sensor satisfies the pressure level, and satisfies the pressure level when the detection value is less than the pressure level. The fuel supply device according to claim 2, wherein the pressure reducing valve is opened.   The fuel supply apparatus according to claim 1 or 3, wherein the control means sets the pressure level according to a situation.   The control means includes
  Pressure difference calculating means (S2) for calculating a pressure difference between the pressure level and the detected value;
  A required amount calculation means (S3) for calculating a required pressure increase amount that is an amount of fuel required to increase the pressure in the reservoir by the pressure difference;
  The said control means (S4-S6) controls opening and closing of the said pressure reduction valve based on the said pressure increase required amount, when the said detected value is less than the said pressure level. The fuel supply device according to any one of the above.   The required amount calculation means uses the following equation where ΔV is the volume change amount of the fuel in the reservoir, ΔP is the pressure difference, V is the volume of fuel in the reservoir, and E is the volume elastic modulus of the fuel in the reservoir. The fuel supply device according to claim 5, wherein the volume change amount ΔV is calculated as the required pressure increase amount.
  ΔV = V × ΔP / E The fuel supply device according to any one of claims 1 to 6, wherein the adjusting means includes a pressure reducing means (24) for reducing the fuel pressure in the reservoir to the pressure level. 8. The valve according to claim 7 , wherein the pressure reducing means is a valve provided in the reservoir and opened so that fuel is released from the reservoir when the fuel pressure in the reservoir exceeds the pressure level. The fuel supply device described in 1. 2. The fuel according to claim 1 , wherein the reservoir includes an expansion / contraction portion (30, 32) provided in contact with the fuel in the reservoir and extending and contracting under the pressure of the fuel in the reservoir. Feeding device.   The fuel supply device according to claim 9, wherein the expansion / contraction part is provided above the inlet (23a) and the outlet (23b) of the reservoir provided separately.   The fuel supply device according to claim 2 or 10, wherein the expansion and contraction part is a gas (30).

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