JP5902443B2 - Common rail decompression control device - Google Patents

Description

  The present invention relates to a common rail pressure reduction control device that reduces the common rail pressure after a key switch is turned off.

In the common rail system, the fuel increased in pressure by the supply pump is temporarily stored in the common rail, which is the accumulator chamber, and the electronic control system controls the opening and closing of the injector nozzles. The required amount of fuel can be injected. Application of the common rail enables ultra-high pressure injection and multistage injection of fuel, and the ultra-high pressure injection makes the fuel atomized and well mixed with air, making it difficult to generate PM (particulate matter) in the exhaust gas. In addition, NO _x (nitrogen oxide) in the exhaust gas can be reduced and noise can be reduced by multi-stage injection.

Japanese Patent Laid-Open No. 10-318028

  By the way, in the common rail system, since the fuel accumulated in the common rail is maintained in a high pressure state even after the engine is stopped, the fuel in the common rail may be ejected when performing maintenance of the common rail system. For this reason, after the engine is stopped, the fuel in the common rail is removed and the pressure is reduced.

  For example, in Patent Document 1, when the key switch is turned off, the solenoid coil of the injector is switched at a fine cycle so that the injector is in the non-injection region, the fuel pressure in the common rail is back leaked in the injector, The pressure is reduced.

  Here, in the electronic control system, when the key switch is turned off, there is a control unit energization time in which the energized state is maintained for a certain time in order to retain various information. Therefore, when the common rail decompression process is performed, it is necessary to perform the control unit energization time after the key switch is turned off. Furthermore, since the common rail in recent years is maintained in an ultra-high pressure state, it takes time for the decompression process. As a result, in the pressure reduction control using the conventional injector in the non-injection region, there is a problem that the fuel pressure in the common rail may not be reliably reduced after the key switch is turned off.

  The present invention has been made in view of the above, and an object of the present invention is to provide a common rail pressure reduction control device capable of reducing the fuel pressure in the common rail in a short time after the key switch is turned off.

In order to solve the above-described problems and achieve the object, a common rail pressure reducing control device according to the present invention includes a pressure reducing valve for reducing the pressure in the common rail by causing the fuel to flow out, and a pressure sensor for detecting the pressure in the common rail. A key switch for driving and stopping the engine, and after the key switch is turned off, the initial drive duty is determined from the pressure detected by the pressure sensor when the key switch is turned off, and the drive duty with the passage of time thereafter is gradually increased. And a control unit that opens the pressure reducing valve at the determined initial driving duty and the determined driving duty with the passage of time thereafter .

  In the common rail pressure-reducing control device according to the present invention, in the above invention, the control unit determines the drive duty as time elapses, the control unit energization time from when the key switch is turned off to when the control unit is turned off. The pressure in the common rail is determined to be a predetermined reduced pressure value.

  In the common rail pressure reduction control device according to the present invention, in the above invention, the control unit predetermines a relationship between a pressure when the key switch is turned off, a maximum allowable discharge amount per driving cycle, and the initial driving duty. The initial drive duty is determined with reference to the held relationship.

  In the common rail pressure reduction control device according to the present invention as set forth in the invention described above, the control unit determines a drive duty associated with the passage of time from a pressure detected by the pressure sensor for each drive cycle for opening and closing the pressure reduction valve. It is characterized by doing.

  In the common rail pressure reduction control device according to the present invention, in the above invention, the control unit determines a final drive duty from the predetermined pressure reduction value, and sets the drive duty within the control unit energization time with respect to time. The drive duty is increased as a linearly approximated drive duty.

  In the common rail pressure reduction control device according to the present invention as set forth in the invention described above, the control unit makes a driving cycle for opening and closing the pressure reducing valve constant.

  In the common rail pressure reducing control device according to the present invention as set forth in the invention described above, the control unit determines a driving cycle for opening and closing the pressure reducing valve in accordance with a pressure when the key switch is turned off.

  According to the present invention, after the key switch is turned off, the fuel discharge amount from the pressure reducing valve becomes the maximum allowable discharge amount per driving cycle based on the pressure detected by the pressure sensor when the key switch is turned off. In this way, the initial drive duty is determined, and the drive duty with the passage of time thereafter is determined to increase the drive duty with the passage of time below the maximum allowable discharge amount per one drive cycle. Since the pressure reducing valve is opened at a driving duty including an initial driving duty, the fuel pressure in the common rail can be reduced in a short time after the key switch is turned off.

FIG. 1 is a schematic diagram showing a schematic configuration of a common rail decompression control device according to an embodiment of the present invention. FIG. 2 is a flowchart showing a pressure reducing valve control processing procedure by the pressure reducing valve control unit shown in FIG. FIG. 3 is a time chart for explaining the opening time of the drive duty with time. FIG. 4 is a time chart showing the time change of the drive duty of the pressure reducing valve within the controller energization time T0 after the key switch is turned off. FIG. 5 is a diagram showing a flow of outputting the open time t by the input of the common rail pressure P. FIG. 6 is a diagram showing the relationship between the common rail pressure and the opening time of the pressure reducing valve. FIG. 7 is a flowchart showing a pressure reducing valve control processing procedure by the pressure reducing valve control unit of the first modification.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a schematic diagram showing a schematic configuration of a common rail decompression control device according to an embodiment of the present invention. In FIG. 1, this common rail pressure reduction control device includes an engine 1, a common rail 2, a fuel tank 3, and a supply pump 4 that supplies fuel from the fuel tank 3 into the common rail 2 to increase the fuel pressure in the common rail 2. An injector group 5 for injecting high-pressure fuel in the common rail 2 from a plurality of injectors, a pressure sensor 6 for detecting the pressure in the common rail 2, and a pressure-reducing valve 7 for reducing the pressure in the common rail 2 by causing the fuel to flow out. And a controller 8 for controlling the engine 1, the injector group 5, the supply pump 4, and the like, and a key switch 10 for driving and stopping the engine 1. The controller 8 includes a pressure reducing valve controller 9 that controls the pressure reducing valve 7 to reduce the pressure in the common rail 2 based on the pressure in the common rail 2 detected by the pressure sensor 6 after the key switch 10 is turned off. The pressure reducing valve 7 may be disposed close to the common rail 2 or provided in the middle of the piping between the common rail 2 and the fuel tank 3.

  The controller 8 monitors the state of the engine 1, drives the supply pump 4 to maintain the pressure in the common rail 2 at a desired high pressure, and performs super-high pressure injection and multistage injection of fuel by the injector group 5. The drive control is performed.

  The pressure reducing valve controller 9 performs a pressure reducing valve control process according to the flowchart shown in FIG. The pressure reducing valve control unit 9 first determines whether or not the key switch 10 is turned off (step S101). If the key switch 10 is turned off (step S101, Yes), the initial value corresponding to the common rail pressure P detected by the pressure sensor 6 is determined. Is determined (step S102). The driving duty is a ratio of the opening time t of the pressure reducing valve 7 to the driving cycle T, which is a cycle for sending a command to open the pressure reducing valve 7 from the pressure reducing valve control unit 9, and the driving cycle T is constant. Corresponds to the opening time t of the pressure reducing valve 7. Therefore, the initial drive duty is t1 / T when the initial opening time t1 of the pressure reducing valve 7 is set as shown in FIG. This initial drive duty is determined by the maximum allowable discharge amount Qmax per drive cycle and the common rail pressure P, as will be described later. The relationship between the initial drive duty (open time t), the maximum allowable discharge amount Qmax per drive cycle, and the common rail pressure P is determined in advance and stored as a function or a map. Therefore, based on this relationship, the initial drive duty (open time t) corresponding to the common rail pressure P detected by the pressure sensor 6 is uniquely determined. Since the drive duty is equivalent to the open time t if the drive cycle is the same, the drive duty will be described below as the open time t instead of the drive duty.

  When the initial opening time t1 is determined, the initial opening time t1 and the final opening time t1 are determined by linear approximation from the initial opening time t1 and the predetermined opening time tn of the control unit energization time T0. The open time t with the passage of time, which is sandwiched between the open time tn and the open time tn, is determined (step S103). Thereafter, drive control for opening the pressure reducing valve 7 at the determined opening time t is performed (step S104), and this process is terminated.

  That is, as shown in FIG. 3, when the initial opening time t is t1, the opening time tn corresponding to the desired reduced pressure value at the end point Tb of the control unit energization time T0 is determined. The open time t1 is connected by a straight line L1 and linear approximation (linear interpolation) is performed with respect to time so that the open time t with the passage of time can be easily obtained. Therefore, the open time t increases linearly and monotonously. If the pressure of the common rail 2 after the key switch is turned off is low and the initial opening time t is t3, the opening time tn and the opening time t3 are approximated by a straight line L3 as shown in FIG. The accompanying open time t is simply obtained. Note that the approximation is not limited to linear approximation, and any approximation can be applied as long as it increases monotonously.

  FIG. 4 is a time chart showing the change over time in the drive duty (opening time of the pressure reducing valve) for opening the pressure reducing valve 7 within the controller energization time T0 after the key switch is turned off. As shown in FIG. 4, the pressure reducing valve 7 is driven at the driving cycle T, and when the initial driving duty t1 / T is determined, the driving duty gradually increases with time, as shown in FIG. To be larger. Therefore, as time elapses, the opening times t1 to tn of the pressure reducing valve 7 have a relationship of t1 <t2 <t3 <t4 <.

  Here, the relationship between the initial opening time t1, the maximum allowable discharge amount Qmax per driving cycle, and the common rail pressure P will be described. In step S102, when the common rail pressure P is input, the initial opening time t1 is determined. This determination process is determined according to the flow shown in FIG.

  As shown in FIG. 5, first, the common rail pressure P is input to a map M <b> 1 indicating the safety characteristics of the pressure reducing valve 7. A map M1 shows the dependency of the maximum allowable discharge amount Qmax per driving cycle on the common rail pressure P, and is represented by a characteristic curve La. That is, Qmax = La (P). The maximum permissible discharge amount Qmax per driving cycle is determined by the mechanical use or thermal use of the pressure reducing valve 7, which decreases as the common rail pressure P increases. Therefore, when the common rail pressure P = P1 is input to the map M1, the maximum allowable discharge amount Qmax = Qmax (P1) per driving cycle is determined by the characteristic curve La.

  Qmax (P1) determined by clearing this safety characteristic and P1 input are input to a map M2 indicating the general discharge performance of the pressure reducing valve 7. The map M2 shows the dependence of the maximum allowable discharge amount Qmax per driving cycle and the common rail pressure P on the initial opening time t, and is indicated by a characteristic curved surface Sa. Expressed by a mathematical formula, t = Sa (Qmax, P). Here, since Qmax (P1) and P1 are input to the map M2, the initial opening time t is uniquely determined. That is, t1 = Sa (Qmax (P1), P1) is determined and output.

  FIG. 6 is a graph showing the relationship between the elapsed time after the key switch is turned off and the corresponding changes in the opening time t of the pressure reducing valve 7 and the common rail pressure P. As shown in FIG. 6, the opening time t increases with time, and accordingly, the common rail pressure P also gradually decreases from P1, and a time point before time point Tb when the control unit energization time T0 ends. The desired pressure reduction value PL is obtained.

  In this embodiment, after the key switch is turned off, an initial driving duty (initial opening time t1) that satisfies the maximum allowable discharge amount Qmax per driving cycle corresponding to the initial common rail pressure P is determined. Since the drive duty with the passage of time is simply determined by linear approximation from the drive duty (open time t1) and the final drive duty (open time tn), the common rail pressure P can be reduced easily and reliably in a short time. be able to. In other words, in this embodiment, the drive duty with the passage of time is increased by linear approximation, and the flow rate from the pressure reducing valve 7 is increased as much as possible even after the passage of time. P can be depressurized.

(Modification 1)
In the above-described embodiment, the open time t with the passage of time is determined by linear approximation of the initial open time t1 and the final open time tn. Each time t is also determined by the same determination as the initial opening time t1.

  FIG. 7 is a flowchart showing a pressure reducing valve control processing procedure by the pressure reducing valve control unit of the first modification. As shown in FIG. 7, first, the pressure reducing valve control unit 9 determines whether or not the key switch 10 is turned off (step S201). When the key switch is off (step S201), the common rail pressure detected by the pressure sensor 6 is acquired (step S202), and the drive duty (open) satisfying the maximum allowable discharge amount Qmax per drive cycle corresponding to the common rail pressure is obtained. Time t) is determined (step S203). Then, drive control is performed to open the pressure reducing valve 7 at the determined drive duty (open time t) (step S204). Thereafter, it is determined whether or not it is within the control unit energization time T0 (step S205). When it is within the control unit energization time T0 (step S205, Yes), in order to further determine the drive duty in the next drive cycle T, the above-described processing of steps S202 to S204 is repeated, and the control unit energization time T0 is determined. If not (No in step S205), the process ends.

  In this modification 1, since the common rail pressure is detected and the drive duty is determined for each drive cycle, the drive duty can be determined and the pressure reducing valve 7 can be controlled with high accuracy and in a short time. The common rail pressure can be reduced.

  In the above-described embodiment and Modification 1, the drive duty is determined with the drive cycle T being constant. However, the present invention is not limited to this. For example, an ON / OFF switching loss, an electromagnetic valve, etc. In consideration of heat generation associated with continuous energization, the driving cycle T may be changed each time based on the common rail pressure after the key switch is turned off.

  Further, in this embodiment and the first modification, the pressure reducing valve 7 is provided independently from the injector group 5, so that the maximum per driving cycle which is the ability of the pressure reducing valve 7 without affecting the injector function. The allowable discharge amount can be set freely.

DESCRIPTION OF SYMBOLS 1 Engine 2 Common rail 3 Fuel tank 4 Supply pump 5 Injector group 6 Pressure sensor 7 Pressure reducing valve 8 Controller 9 Pressure reducing valve control part 10 Key switch

Claims (7)

A pressure reducing valve for reducing the pressure in the common rail by letting the fuel flow out;
A pressure sensor for detecting the pressure in the common rail;
A key switch to drive and stop the engine,
After the key switch is turned off, the initial drive duty is determined from the pressure detected by the pressure sensor when the key switch is turned off, and the drive duty is gradually increased with the passage of time thereafter. A control unit that opens the pressure reducing valve at a drive duty and a drive duty associated with the determined subsequent time passage ; and
A common rail pressure-reducing control device.   The control unit determines a drive duty over time so that the pressure in the common rail becomes a predetermined reduced pressure value within a control unit energization time from when the key switch is turned off until the energization of the control unit is turned off. The common rail pressure-reducing control device according to claim 1.   The control unit holds in advance a relationship among the pressure when the key switch is off, the maximum allowable discharge amount per driving cycle, and the initial driving duty, and refers to the held relationship to determine the initial driving duty. The common rail pressure-reducing control device according to claim 1, wherein the common rail pressure-reducing control device is determined.   The said control part determines the drive duty accompanying time passage from the pressure which the said pressure sensor detects for every drive period which opens and closes the said pressure reduction valve, It is any one of Claims 1-3 characterized by the above-mentioned. The common rail decompression control device described. The control unit determines a final drive duty from the predetermined reduced pressure value, and increases the drive duty as a drive duty that linearly approximates the drive duty within the control unit energization time with respect to time. The common rail decompression control device according to claim 2 .   The common rail pressure-reducing control device according to claim 1, wherein the control unit makes a driving cycle for opening and closing the pressure-reducing valve constant.   The common rail pressure-reducing control device according to any one of claims 1 to 6, wherein the control unit determines a driving cycle for opening and closing the pressure-reducing valve according to a pressure when the key switch is turned off.

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