JP2010084726A - Rail pressure control device for common rail type diesel engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rail pressure control device for a common rail type diesel engine reducing electric power consumption of a pressure reducing valve for preventing abnormal rise of rail pressure and keeping deterioration of fuel economy caused by the same at the minimum. <P>SOLUTION: In normal time when rail pressure Prail does not abnormally rises, valve opening pressure Pset of the pressure reducing valve for system protection is controlled to normal set pressure Pnml at high pressure side by offset quantity Pofst from target rail pressure tgtPrail and electric power consumption of the pressure reducing valve is reduced, and the valve opening pressure Pset of the pressure reducing valve is increased to upper limit set pressure Plmtl and the pressure reducing valve is opened when rail pressure Prail reaches the upper limit set pressure Plmtl if abnormal rise of the rail pressure is determined. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a common rail type diesel engine, and more particularly to a rail pressure control device for reducing the pressure by leaking fuel in a common rail by opening a pressure reducing valve when the rail pressure rises abnormally.

  In order to respond to the recent tightening of exhaust gas regulations, a common rail type diesel engine in which high pressure fuel supplied from a fuel pump is accumulated in a common common rail and supplied to the fuel injection valve of each cylinder has been put into practical use. In this type of diesel engine, the accuracy of the fuel injection amount and the injection timing can be improved, or various purpose fuel injections such as pilot injection and post injection can be arbitrarily added before and after the conventional main injection. One of the requirements for making the best use of the features is to control the rail pressure appropriately with respect to the operating state of the engine.

Therefore, for example, an intake amount adjusting valve is provided on the suction side of the fuel pump, the amount of fuel sucked into the fuel pump is limited according to the opening of the intake amount adjusting valve, and the amount of fuel discharged from the fuel pump is set accordingly. By adjusting, the actual rail pressure is controlled to the target rail pressure obtained from the operating state of the engine.
Various countermeasures have been conventionally taken for appropriate rail pressure control. For example, the technique of Patent Document 1 can be cited. The technique of Patent Document 1 focuses on the fact that a tracking delay occurs in the actual rail pressure with respect to the target rail pressure during a pressure transient in which the rail pressure is changed following the change in the operating state of the engine. A pressure reducing valve is connected to the common rail, and the internal fuel leaks to the fuel tank side when the valve is opened. The pressure is reduced on condition that the actual rail pressure is higher than the target rail pressure by a predetermined value or more. The valve is opened and the common rail is depressurized due to fuel leakage to reduce the delay in tracking the rail pressure.

The method of using the pressure reducing valve connected to the common rail is not limited to the above-mentioned Patent Document 1, and is also used for protecting a common rail system, for example. Specifically, rail pressure rises abnormally when the fuel pump becomes uncontrolled and the fuel supply to the common rail becomes excessive due to troubles such as the open adjustment of the intake pressure adjusting valve for rail pressure control. As a result, the common rail system may be damaged. Therefore, for example, when the actual rail pressure exceeds the preset upper limit set pressure in consideration of the pressure limit of the common rail system, damage is avoided by opening the pressure reducing valve to reduce the pressure in the common rail.
JP 2002-371940 A

  By the way, when a pressure reducing valve is used to prevent an abnormal increase in rail pressure, it is necessary to control and hold the valve opening pressure of the pressure reducing valve at the above-described upper limit set pressure in preparation for the abnormal increase in rail pressure. There are various types of pressure reducing valves.For example, when using a normally open pressure reducing valve that keeps the valve open at the time of de-energization and increases the valve opening pressure according to an increase in the duty ratio of the drive current, It is always necessary to supply a current having a large duty ratio corresponding to the upper limit set pressure to the pressure reducing valve. The increase in power consumption caused by this causes an increase in the power generation load of the alternator, which in turn causes a problem that fuel consumption deteriorates due to an increase in engine load.

  The present invention has been made to solve such a problem, and an object of the present invention is to reduce the power consumption of the pressure reducing valve for preventing an abnormal increase in rail pressure, thereby resulting in fuel consumption. It is an object of the present invention to provide a rail pressure control device for a common rail type diesel engine that can suppress deterioration to a minimum.

  In order to achieve the above object, according to the first aspect of the present invention, the high pressure fuel supplied from the fuel pump is accumulated in the common rail, the rail pressure is controlled to the target rail pressure corresponding to the operating state of the engine, and the fuel in the common rail is controlled. A common rail diesel engine that is supplied to the fuel injection valve of each cylinder and injects into the cylinder, and has a characteristic of increasing the valve opening pressure in response to an increase in supply power, and when the rail pressure reaches the valve opening pressure. When an abnormal rise is determined by a pressure reducing valve that can open and leak the fuel in the common rail to depressurize, a rail pressure abnormal increase determination means that determines an abnormal increase in rail pressure, and a rail pressure abnormal increase determination means Then, the valve opening pressure of the pressure reducing valve is controlled to the upper limit set pressure set in advance based on the pressure limit of the common rail, and when the abnormal increase is not determined by the rail pressure abnormal increase determining means, the pressure is decreased. It is obtained by a pressure reducing valve control means for controlling the valve opening pressure of the valve to a normal set pressure which is set to the low pressure side than the upper limit set pressure.

  Therefore, when the rail pressure rises abnormally, the valve opening pressure of the pressure reducing valve is controlled to the upper limit set pressure set based on the pressure limit of the common rail. Therefore, when the abnormally increased rail pressure reaches the upper limit set pressure, the pressure is reduced. The valve is opened and the common rail is depressurized due to fuel leakage, preventing system damage. On the other hand, at the normal time when the rail pressure does not rise abnormally, the valve opening pressure of the pressure reducing valve is controlled to the normal set pressure lower than the upper limit set pressure. With a pressure reducing valve that increases the valve opening pressure in response to an increase in power supply, it is necessary to increase the power supply to increase the valve opening pressure, so the valve opening pressure of the pressure reducing valve during normal operation is reduced. This leads to a reduction in the power supplied to the pressure reducing valve, that is, the power consumption. Therefore, the power generation load of the alternator is reduced, and the deterioration of the fuel consumption is suppressed to the minimum due to the reduction in the engine load.

According to a second aspect of the present invention, in the first aspect, when the pressure reducing valve control means determines that the abnormal increase is not determined by the rail pressure abnormal increase determination means, the pressure is controlled in advance from the target rail pressure or the rail pressure controlled based on the target rail pressure. A normal set pressure is set on the high pressure side by the set offset, and the valve opening pressure of the pressure reducing valve is controlled based on the normal set pressure.
Therefore, the actual rail pressure is controlled following the target rail pressure set according to the operating state of the engine, and the normal set is set on the high pressure side by an offset amount relative to this target rail pressure or actual rail pressure. The valve opening pressure of the pressure reducing valve is controlled so as to be a pressure. As a result, at normal times when the rail pressure does not rise abnormally, the normal set pressure is always controlled to a value slightly higher than the rail pressure, the rail pressure reaches the normal set pressure, and the pressure reducing valve is opened carelessly. In addition, the power consumption of the pressure reducing valve can be reduced to the maximum by controlling the normal set pressure to the minimum required low pressure side.

  A third aspect of the present invention provides the fuel temperature correlation value detecting means for detecting a value correlated with the temperature of the fuel flowing through the pressure reducing valve when the valve is opened, wherein the pressure reducing valve control means has a rail pressure abnormality. In order to compensate for the influence of the temperature of the fuel flowing through the pressure reducing valve on the relationship between the control amount of the pressure reducing valve and the opening pressure of the pressure reducing valve when an abnormal rise is not determined by the rise determining means, the normal set pressure is the fuel temperature correlation value. Correction is made based on the fuel temperature correlation value detected by the detection means, and the valve opening pressure of the pressure reducing valve is controlled based on the corrected normal set pressure.

Therefore, since the influence of the fuel temperature is compensated by correcting the normal set pressure based on the fuel temperature correlation value detected by the fuel temperature correlation value detecting means, the valve opening pressure of the pressure reducing valve is based on the appropriate normal rail pressure. Is controlled, and further reduction of power consumption is achieved while preventing inadvertent opening of the pressure reducing valve.
According to a fourth aspect of the present invention, in the first to third aspects, when the pressure reducing valve control means determines that the rail pressure abnormal increase determination means determines an abnormal increase, the upper limit set pressure is used as a feedforward component, The valve opening pressure of the pressure reducing valve is fed back based on the P term and I term set as feedback terms from the deviation from the rail pressure.

  Therefore, the upper limit set pressure is applied as a feedforward component simultaneously with the determination of the abnormal rise by the rail pressure abnormal rise judgment means, and the valve opening pressure is controlled to increase stepwise up to the upper limit set pressure. In contrast, it is possible to quickly reduce the pressure in the common rail by opening the pressure reducing valve without delay, and after that, feedback based on the P term and the I term can accurately maintain the valve opening pressure at the upper limit set pressure. Become.

  According to a fifth aspect of the present invention, there is provided the fuel temperature correlation value detecting means for detecting a value correlated with the temperature of the fuel flowing through the pressure reducing valve when the valve is opened. In order to compensate for the influence of the temperature of the fuel flowing through the pressure reducing valve on the relationship between the control amount of the pressure reducing valve and the opening pressure of the pressure reducing valve when an abnormal rise is determined by the rise determining means, the upper limit set pressure is correlated with the fuel temperature. Correction is performed based on the fuel temperature correlation value detected by the value detection means, and the valve opening pressure of the pressure reducing valve is controlled based on the corrected upper limit set pressure.

  Therefore, since the influence of the fuel temperature is compensated by correcting the upper limit set pressure based on the fuel temperature correlation value detected by the fuel temperature correlation value detecting means, the valve opening pressure of the pressure reducing valve is based on the appropriate upper limit set pressure. Is controlled to reliably prevent system damage.

As described above, according to the rail pressure control device of the common rail diesel engine of the first aspect of the present invention, the power consumption of the pressure reducing valve for preventing the abnormal increase in rail pressure can be reduced, and the fuel consumption caused by this can be reduced. Can be minimized.
According to the rail pressure control device of the common rail type diesel engine of the invention of claim 2, in addition to claim 1, the rail pressure is not abnormally increased by setting the target rail pressure or the normal set pressure following the rail pressure. The power consumption of the pressure reducing valve can be reduced to the maximum while reliably preventing unnecessary opening of the pressure reducing valve at normal times.

According to the rail pressure control device for the common rail type diesel engine of the third aspect of the invention, in addition to the first or second aspect, by compensating for the influence of the fuel temperature, the rail pressure is not increased abnormally. The power consumption of the pressure reducing valve can be reduced to the maximum while reliably preventing the necessary pressure reducing valve from opening.
According to a rail pressure control device for a common rail type diesel engine according to a fourth aspect of the invention, in addition to the first to third aspects, the valve opening pressure of the pressure reducing valve is set to the upper limit set pressure by feedback control using the upper limit set pressure as a feedforward component. Therefore, the system can be more appropriately controlled, and the system damage when the rail pressure is abnormally increased can be prevented more reliably.

  According to the rail pressure control device of the common rail type diesel engine of the fifth aspect of the invention, in addition to the first to fourth aspects, by compensating for the influence of the fuel temperature, the system damage at the time when the rail pressure is abnormally increased is further reduced. It can be surely prevented.

Hereinafter, an embodiment of a rail pressure control device for a common rail type diesel engine embodying the present invention will be described.
FIG. 1 is an overall configuration diagram showing a rail pressure control device of a common rail type diesel engine according to the present embodiment.
Each cylinder of the diesel engine 1 is provided with a fuel injection valve 2, and each fuel injection valve 2 is connected to a common common rail 3. The common rail 3 is connected to a supply pump 6 (fuel pump) through a pair of supply fuel passages 5 each having a check valve 4, and the supply pump 6 has a filter 7 and a feed fuel having an electromagnetic intake amount adjusting valve 8. The feed pump 10 is connected to the fuel tank 12 through the tank fuel path 11.

Although FIG. 1 shows the supply pump 6 and the feed pump 10 separately, the actual pumps 6 and 10 are integrated and connected by a common drive shaft 13 and are not shown in the figure. Although not shown, both pumps 6 and 10 are driven by the engine 1 via the drive shaft 13.
The fuel in the fuel tank 12 is pumped up by the feed pump 10 and supplied to the supply pump 6 through the tank fuel path 11 and the feed fuel path 9, and further pressurized by the supply pump 6 to the common rail 3 through the supply fuel path 5. Supplied. The fuel intake amount of the supply pump 6 is limited according to the opening of the intake amount adjustment valve 8, and the fuel discharge amount of the supply pump 6 is controlled accordingly, so that the fuel pressure (rail pressure) in the common rail 3 will be described later. Adjusted to rail pressure. Thus, the high-pressure fuel accumulated in the common rail 3 is always supplied to the fuel injection valve 2 of each cylinder, and the fuel injection valve 2 is opened at a predetermined crank angle near the compression top dead center of each cylinder. Fuel is injected into the cylinder for combustion.

  One side of the common rail 3 is connected to the fuel tank 12 via a leak fuel path 14, and a pressure reducing valve 15 is provided in the leak fuel path 14. The pressure reducing valve 15 closes the leak fuel passage 14 with a predetermined valve opening pressure to block the fuel flow. When the rail pressure rises and exceeds the valve opening pressure of the pressure reducing valve 15, the pressure reducing valve 15 opens. Then, the fuel in the common rail 3 is leaked to the fuel tank 12 side through the leak fuel passage 14. The pressure reducing valve 15 is configured as a so-called normally open type that is maintained in an open state when no drive current is supplied and is adjusted to increase the valve opening pressure in accordance with an increase in the duty ratio of the drive current when the current is supplied. .

The pressure reducing valve 15 does not necessarily need to be kept fully open when the valve is not energized as long as the valve opening pressure is increased according to an increase in the duty ratio of the drive current. The pressure reducing valve 15 whose valve opening pressure is set to a predetermined value (for example, 30 MPa) may be used.
On the other hand, an input / output device (not shown), a storage device (ROM, RAM, etc.) for storing control programs and control maps, a central processing unit (CPU), a timer counter, etc. Control unit) is installed. On the input side of the ECU 21, a rail pressure sensor 22 (rail pressure abnormal rise determination means) that detects the rail pressure Prail, a rotation speed sensor 23 that detects the rotation speed Ne of the engine 1, and a leak fuel passage 14 are installed in the pressure reducing valve. Various sensors such as a fuel temperature sensor 24 (fuel temperature correlation value detecting means) for detecting the fuel temperature Tf leaked from the fuel tank 15 and an accelerator sensor 25 for detecting the accelerator opening θacc of the vehicle are connected. Various devices such as the fuel injection valve 2, the intake amount adjustment valve 8, and the pressure reducing valve 15 are connected to the output side of the ECU 21.

  The ECU 21 sets the target value of the fuel injection amount and the injection timing by the fuel injection valve 2 based on various information about the engine operating state such as the accelerator opening θacc detected by the accelerator sensor 25 and the rotational speed Ne detected by the rotational speed sensor 23. The target rail pressure tgtPrail and the like of the common rail 3 are set, for example, the fuel injection valve 2 is driven and controlled based on the target value of the fuel injection amount and injection timing, and the intake amount adjusting valve 5 is opened based on the target rail pressure tgtPrail. The actual rail pressure Prail is feedback-controlled to the target rail pressure tgtPrail, thereby operating the engine 1.

  The control of the pressure reducing valve 15 is executed for the purpose of protecting the common rail system, and basically the rail pressure Prail is controlled by controlling the valve opening pressure of the pressure reducing valve 15 to the upper limit set pressure Plmt in consideration of the system pressure limit. In order to solve the problem of power consumption of the pressure reducing valve 15 described in [Problems to be Solved by the Invention] At normal times when the rail pressure Prail does not rise abnormally, the control mode of the pressure reducing valve 15 based on another valve opening pressure is executed. Therefore, the control of the valve opening pressure of the pressure reducing valve 15 will be described in detail according to the control block diagram shown in FIG.

First, the target rail pressure tgtPrail applied in the rail pressure control and the preset offset amount Pofst are input to the adding unit 31. The adding unit 31 calculates the normal set pressure Pnml by adding the offset amount Pofst to the target rail pressure tgtPrail, and the calculated normal set pressure Pnml is input to the F / F amount switching unit 32 and the deviation calculating unit 33, respectively.
By the rail pressure control based on the target rail pressure tgtPrail, the rail pressure Prail is controlled following the target rail pressure tgtPrail set according to the engine operating state. The rail pressure Prail always has an error on the high pressure side or the low pressure side with respect to the target rail pressure tgtPrail. The offset amount Pofst is set as a value slightly larger than the maximum error of the rail pressure Prail that can be generated at this time, so that the normal set pressure Pnml is set at a normal time when the rail pressure Prail does not rise abnormally. It is always set as a value slightly higher than the rail pressure Prail, and the rail pressure Prail does not exceed this normal set pressure Pnml.

  In the deviation calculating unit 33, a deviation ΔP1 (= Pnml−Prail) between the normal set pressure Pnml and the actual rail pressure Prail detected by the rail pressure sensor 22 is calculated. The calculated deviation ΔP1 is input to the mode command unit 34. When the mode command unit 34 compares the deviation ΔP1 with 0 and determines that it is a positive value (ΔP1> 0), the normal time control mode is selected. When it is determined that the deviation ΔP1 is 0 or a negative value (ΔP1 ≦ 0), it is considered that the rail pressure Prail is abnormally increased, and the abnormal time control mode is selected, and the selected control mode is the F / F amount switching unit 32. And it outputs to the F / B amount switching part 39 mentioned later. In FIG. 2, switching of the F / F amount switching unit 32 and the F / B amount switching unit 39 to the normal time control mode is represented by +, and switching to the abnormal time control mode is represented by-.

  The F / F amount switching unit 32 is inputted with the above-mentioned normal set pressure Pnml and the upper limit set pressure Plmt set in advance in consideration of the system pressure limit, and the F / F amount switching unit 32 receives the mode command unit 34. The normal set pressure Pnml is output to the duty ratio converter 35 as the valve opening pressure Pset when the switch to the normal time control mode is commanded, and the upper limit when the switch to the abnormal time control mode is commanded. The set pressure Plmt is output to the duty ratio converter 35 as the valve opening pressure Pset. The fuel temperature Tf detected by the fuel temperature sensor 24 is input to the duty ratio conversion unit 35 together with the valve opening pressure Pset, and is supplied to the pressure reducing valve 15 from a predetermined map based on the valve opening pressure Pset and the fuel temperature Tf. The duty ratio of the drive current is calculated and input to the adder 36.

  The reason why the fuel temperature Tf is reflected in the duty ratio calculation process is to compensate for the influence of the fuel temperature Tf on the valve opening pressure Pset of the pressure reducing valve 15. That is, the inventor changes the fuel temperature Tf flowing through the pressure reducing valve 15 and changes the duty ratio of the drive current supplied to the pressure reducing valve 15 (in other words, the control amount of the pressure reducing valve 15) and the valve opening of the pressure reducing valve 15. A test for measuring the pressure Pset was performed, and it was confirmed that the valve opening pressure Pset was different when the fuel temperature Tf was changed even at the same duty ratio. The cause is that the operating state of the fuel pressure on the pressure reducing valve 15 slightly changes depending on the viscosity of the fuel. As a result, even if the pressure reducing valve 15 is controlled with the same duty ratio, the pressure reducing valve 15 opens at different pressures. It is estimated that a phenomenon will occur.

  Therefore, in view of such valve opening characteristics of the pressure reducing valve, in other words, the influence of the fuel temperature Tf on the relationship between the duty ratio (control amount) of the pressure reducing valve 15 and the valve opening pressure Pset of the pressure reducing valve 15 can be compensated. In this case, the map characteristic of the duty ratio converter 35 is set based on the test result so that the same valve opening pressure Pset can always be achieved at the same duty ratio regardless of the fuel temperature Tf.

  On the other hand, the upper limit set pressure Plmt and the actual rail pressure Prail are input to the deviation calculating section 37, and the deviation calculating section 37 calculates a deviation ΔP2 (= Plmt−Prail) between the upper limit set pressure Plmtl and the actual rail pressure Prail. The calculated deviation ΔP2 is input to the F / B amount calculation unit 38, and the F / B amount calculation unit 38 calculates P and I terms as feedback terms for the valve opening pressure Pset of the pressure reducing valve 15 based on the deviation ΔP2. . The calculated P term and I term are input to the F / B amount switching unit 39, and when the F / B amount switching unit 39 is instructed to switch from the mode command unit 34 to the normal time control mode, 0 is output. Is output to the adder 36 as the F / B amount, and when the switch to the abnormal time control mode is commanded, the P term and the I term are output to the adder 36 as the F / B amount.

In the adding unit 36, the duty ratio of the drive current input from the duty ratio converting unit 35 and the 0 or P term and I term input from the F / B amount switching unit 39 are added, and the final duty after addition is added. The ratio is applied to the valve opening pressure control of the pressure reducing valve 15.
Next, the control status of the valve opening pressure Pset of the pressure reducing valve 15 based on the duty ratio of the drive current calculated by the processing of the ECU 21 will be described in detail according to the time chart shown in FIG.

  A period before the abnormality determination in FIG. 3 indicates a normal time when the rail pressure Prail is not abnormally increased. At this time, due to feedback based on the target rail pressure tgtPrail in the rail pressure control, the actual rail pressure Prail (shown by a thick solid line in FIG. 3) changes with the target rail pressure tgtPrail (see FIG. 3) corresponding to the engine operating state. 3, and a normal set pressure Pnml (indicated by a thick one-dot chain line in FIG. 3) is set on the high pressure side by an offset amount Pofst from the target rail pressure tgtPrail. ing.

  Since the normal rail pressure Prail does not exceed the normal set pressure Pnml, the normal command mode is selected by the mode command unit 34, and the F / F amount switching unit 32 opens the valve in response to this control mode command. The normal set pressure Pnml is selected as the pressure Pset, the duty ratio is calculated by the duty ratio converter 35 based on the normal set pressure Pnml, and is input to the adder 36. On the other hand, 0 is input from the F / B amount switching unit 38 to the adding unit 36 based on the command in the normal control mode, and as a result, the drive current supplied to the pressure reducing valve 15 corresponds to the normal set pressure Pnml. It is controlled to a duty ratio (indicated by a thick one-dot chain line in FIG. 3), and the valve opening pressure Pset of the pressure reducing valve 15 is kept at the normal set pressure Pnml (pressure reducing valve control means).

  The rail pressure Prail does not exceed the normal set pressure Pnml unless it rises abnormally. However, if the supply pump 6 falls into an uncontrolled state due to troubles such as open sticking of the intake amount adjusting valve 8 that controls the rail pressure. The fuel supply to the common rail 3 becomes excessive, and an abnormal increase in the rail pressure Prail occurs. The period after the abnormality determination in FIG. 3 indicates the abnormal rise of the rail pressure Prail. At this time, when the abnormally increased rail pressure Prail reaches the normal set pressure Pnml, the mode command unit 34 determines that the rail pressure Prail is abnormally increased, and the abnormal time control mode is selected instead of the normal time control mode ( Rail pressure abnormality rise determining means), upon receiving this control mode switching command, the F / F amount switching unit 32 selects the upper limit set pressure Plmt as the valve opening pressure Pset, and the duty ratio conversion unit 35 based on the upper limit set pressure Plmt. The duty ratio is calculated and input to the adder 36. On the other hand, based on the switching command to the control mode at the time of abnormality, the P term and the I term are input from the F / B amount switching unit 39 to the adding unit 36, and these P term and I term are based on the duty ratio after addition. The valve opening pressure Pset of the pressure reducing valve 15 is controlled.

  As a result, the upper limit set pressure Plmt is used as a feedforward component, and feedback control of the valve opening pressure Pset is executed based on the P term and I term obtained as a feedback term from the deviation ΔP2 between the upper limit set pressure Plmtl and the actual rail pressure Prail. As a result, the valve opening pressure Pset of the pressure reducing valve 15 is switched from the normal set pressure Pnml to the upper limit set pressure Plmt on the higher pressure side (pressure reducing valve control means). Accordingly, when the abnormally increased rail pressure Prail reaches the upper limit set pressure Plmt, the pressure reducing valve 15 is opened, the inside of the common rail 3 is reduced due to fuel leak, and the system is prevented from being damaged. It is kept at the upper limit set pressure Plmt.

  Note that the valve opening pressure Pset of the pressure reducing valve 15 is controlled to the normal set pressure Pnml before the rail pressure Prail abnormally rises, but at the moment when the rail pressure Prail reaches the normal set pressure Pnml, the valve opening pressure Pset is controlled. Since the upper limit set pressure Plmt on the higher pressure side is switched in response to the mode switching, the pressure reducing valve 15 is not temporarily opened at the moment of the control mode switching. However, the threshold for determining the switching of the control mode is not limited to the normal set pressure Pnml, and may be set to a predetermined value on the lower pressure side.

  As described above, at the normal time when the rail pressure Prail does not rise abnormally, the valve opening pressure Pset of the pressure reducing valve 15 is maintained at the normal set pressure Pnml on the high pressure side by the offset amount Pofst from the target rail pressure tgtPrail. The normal set pressure Pnml at the time is the upper limit set pressure Plmt which is the valve opening pressure Pset at the time of abnormality, in other words, the valve opening pressure at which the conventional pressure reducing valve described in [Problems to be Solved by the Invention] is always controlled. Compared with, the value is significantly lower.

  That is, according to the present invention, it is not always necessary to increase the valve opening pressure Pset of the pressure reducing valve 15 to the upper limit set pressure Plmtl during normal times when the rail pressure Prail is not abnormally increased, so that the rail pressure control is not hindered. It is noted that there is room for further lowering the valve opening pressure Pset as long as it is higher than the control region of the rail pressure Prail. In the normally open pressure reducing valve 15 that is held open when the power is not supplied, the duty ratio of the drive current needs to be increased in order to increase the valve opening pressure Pset. Lowering the valve pressure Pset leads to a reduction in power consumption as well as the duty ratio of the drive current. Controlling the valve opening pressure Pset by providing the common rail 3 with the pressure reducing valve 15 in preparation for the abnormal rise of the rail pressure Prail is unavoidable, but it is inevitable that the electric pressure is reduced in this way. By reducing the power consumption required for driving the valve 15, the power generation load of the alternator driven by the engine 1 can be reduced, and as a result, the engine load can be reduced and deterioration of fuel consumption can be suppressed to a minimum.

  In addition, in the present embodiment, the normal set pressure Pnml is not set to a fixed value, but is controlled to a value on the high pressure side by an offset amount Pofst that always anticipates a control error of the rail pressure Prail with respect to the target rail pressure tgtPrail. Accordingly, it is possible to prevent the pressure reducing valve 15 from being inadvertently opened even if the rail pressure Prail does not rise abnormally, and then to the minimum necessary low pressure side. By controlling the set pressure Pnml, the power consumption can be reduced to the maximum.

  However, as is apparent from the above idea of the present invention, it is not always necessary to control the normal set pressure Pnml following the target rail pressure tgtPrail. For example, the actual rail pressure Prail controlled based on the target rail pressure tgtPrail It may be detected by a pressure sensor, and the normal set pressure Pnml may be controlled following the rail pressure Prail. In addition, the normal set pressure Pnml is not variably controlled following the target rail pressure tgtPrail or the rail pressure Prail, for example, slightly higher than the maximum pressure in the control region in which the rail pressure Prail can be controlled by the rail pressure control at the normal time. The normal set pressure Pnml may be set as a fixed value.

  On the other hand, the duty ratio converter 35 calculates the duty ratio from a map reflecting the fuel temperature Tf regardless of whether the normal set pressure Pnml or the upper limit set pressure Plmt is input, and reduces the pressure based on the calculated duty ratio. The drive current of the valve 15 is controlled. As a result, the same valve opening pressure Pset is always achieved regardless of the fuel temperature Tf at both the normal time and the abnormal increase in the rail pressure Prail, and the influence of the fuel temperature Tf is reliably compensated.

  For example, in the normal state shown in FIG. 3, the control state of the valve opening pressure Pset of the pressure reducing valve 15 when the normal set pressure Pnml is set lower based on the duty ratio without considering the fuel temperature Tf is indicated by a thin one-dot chain line. However, in this case, the pressure reducing valve 15 may be inadvertently opened by a slight change in the rail pressure Prail to the high pressure side. Although not shown, conversely, when the normal set pressure Pnml is set high, extra power consumption is required to drive the pressure reducing valve 15. On the other hand, if the valve opening pressure Pset of the pressure reducing valve 15 is controlled based on the duty ratio that does not consider the fuel temperature Tf when the rail pressure Prail is abnormally increased, the system damage cannot be reliably prevented depending on the case by improper control. There is a possibility.

  These concerns can be surely eliminated by setting the duty ratio reflecting the fuel temperature Tf, and in normal times, by setting an appropriate normal set pressure Pnml, the pressure reducing valve 15 can be prevented from being opened carelessly and further consumed. On the other hand, when the rail pressure Prail is abnormally increased, system breakage can be prevented more reliably by feedback control of the valve opening pressure Pset of the pressure reducing valve 15 based on the duty ratio of an appropriate feedforward component. be able to.

  By the way, although the abnormal rise of the rail pressure Prail may occur suddenly, even in that case, when the abnormally increased rail pressure Prail reaches the upper limit set value Plmtl, the upper limit set is already set from the normal set pressure Pnml. It is necessary to open the pressure reducing valve 15 immediately after completing the switching of the valve opening pressure Pset to the value Plmtl. In this embodiment, when the rail pressure Prail increases abnormally, the upper limit set pressure Plmt is used as a feedforward component, and the pressure is reduced based on the P term and I term obtained as a feedback term from the deviation ΔP2 between the upper limit set pressure Plmtl and the actual rail pressure Prail. The valve opening pressure Pset of the valve 15 is feedback controlled. For this reason, the upper limit set pressure Plmt is applied as a feedforward component simultaneously with the switching to the abnormal time control mode (that is, the switching of the F / F amount switching unit 32 from − to +), and the valve opening pressure Pset is set to the upper limit set. The pressure is controlled to increase in a stepwise manner up to the pressure Plmt. Therefore, the pressure reducing valve 15 can be opened without delay and the pressure in the common rail 3 can be quickly reduced without delay when the rail pressure Prail rises abnormally. Thereafter, the pressure reducing valve 15 is opened by feedback based on the P term and the I term. The pressure Pset, and thus the rail pressure Prail, can be accurately maintained at the upper limit set pressure Plmt, and system damage can be more reliably prevented by these factors.

  This is the end of the description of the embodiment, but the aspect of the present invention is not limited to this embodiment. For example, in the above embodiment, the offset amount Pofst is set as a fixed value in consideration of the control error of the actual rail pressure Prail with respect to the target rail pressure tgtPrail. However, the probability that the rail pressure Prail at the normal time exceeds the normal set pressure Pnml varies depending on, for example, the level of the rail pressure Prail and the fluctuation state. Therefore, if the offset amount Pofst is variably controlled, the pressure decreases. The valve opening pressure Pset of the valve 15 can be controlled more appropriately.

  Therefore, for example, an optimal offset amount Pofst may be set in advance as a map according to the operating region of the engine 1, and the normal set pressure Pnml may be set based on the offset amount Pofst read from the map based on the engine operating region. . Further, the larger the amount of change per time when the target rail pressure tgtPrail (or rail pressure Prail) increases, the higher the probability that the rail pressure Prail will exceed the normal set pressure Pnml, and the offset amount Pofst is determined. The normal set pressure Pnml may be set based on the corrected offset amount Pofst.

In the above embodiment, feedback control using the upper limit set pressure Plmt as a feedforward component when the rail pressure Prail is abnormally increased is performed. However, instead of this, normal PID control may be used.
In the above embodiment, the duty ratio of the drive current is set to reflect the fuel temperature Tf so as to compensate for the influence of the fuel temperature Tf. However, the processing is not necessarily performed. The duty ratio may be set directly from the valve opening pressure Pset.

It is a whole lineblock diagram showing the rail pressure control device of a common rail type diesel engine of an embodiment. It is a control block diagram of ECU for setting the duty ratio of the drive current supplied to the pressure reducing valve. It is a time chart which shows the control condition of the valve opening pressure of the pressure-reduction valve at the time of normal time and the time of an abnormal raise of rail pressure.

Explanation of symbols

1 Engine 2 Fuel Injection Valve 3 Common Rail 6 Supply Pump (Fuel Pump)
15 Pressure reducing valve 21 ECU (Rail pressure abnormality rise determining means, pressure reducing valve control means)
22 Rail pressure sensor (Rail pressure abnormality rise judging means)
24 Fuel temperature sensor (Fuel temperature correlation value detection means)

Claims (5)

The high-pressure fuel supplied from the fuel pump is accumulated in the common rail, the rail pressure is controlled to the target rail pressure according to the operating state of the engine, and the fuel in the common rail is supplied to the fuel injection valve of each cylinder to enter the cylinder In the common rail type diesel engine to be injected,
A pressure-reducing valve having a characteristic of increasing the valve opening pressure in response to an increase in power supply, and capable of opening the rail when the rail pressure reaches the valve opening pressure and leaking fuel in the common rail to reduce the pressure;
Rail pressure abnormality rise determining means for determining an abnormal increase in rail pressure;
When an abnormal increase is determined by the rail pressure abnormal increase determination means, the valve opening pressure of the pressure reducing valve is controlled to an upper limit set pressure set in advance based on the pressure limit of the common rail, and the rail pressure abnormal increase determination A pressure reducing valve control means for controlling the valve opening pressure of the pressure reducing valve to a normal set pressure set to a lower pressure side than the upper limit set pressure when an abnormal rise is not determined by the means. Rail pressure control device for diesel engines.   The pressure reducing valve control means is higher by a preset offset than the target rail pressure or the rail pressure controlled based on the target rail pressure when the abnormal rise is not judged by the rail pressure abnormal rise judging means. The rail pressure control device for a common rail type diesel engine according to claim 1, wherein the normal set pressure is set on the side, and the valve opening pressure of the pressure reducing valve is controlled based on the normal set pressure. A fuel temperature correlation value detecting means for detecting a value correlated with the temperature of the fuel flowing through the pressure reducing valve when the valve is opened;
The pressure reducing valve control means is configured to control a fuel temperature flowing through the pressure reducing valve with respect to a relationship between a control amount of the pressure reducing valve and a valve opening pressure of the pressure reducing valve when an abnormal increase is not determined by the rail pressure abnormality increase determining means. In order to compensate for the influence, the normal set pressure is corrected based on the fuel temperature correlation value detected by the fuel temperature correlation value detecting means, and the valve opening pressure of the pressure reducing valve is controlled based on the corrected normal set pressure. The rail pressure control device of a common rail type diesel engine according to claim 1 or 2, wherein   The pressure reducing valve control means sets the upper limit set pressure as a feedforward component when the abnormal rise is determined by the rail pressure abnormal rise determination means, and sets as a feedback term from a deviation between the upper limit set pressure and the actual rail pressure. 4. The rail pressure control device for a common rail diesel engine according to claim 1, wherein the valve opening pressure of the pressure reducing valve is fed back based on the P term and the I term. A fuel temperature correlation value detecting means for detecting a value correlated with the temperature of the fuel flowing through the pressure reducing valve when the valve is opened;
The pressure reducing valve control means is configured to detect a temperature of a fuel flowing through the pressure reducing valve with respect to a relationship between a control amount of the pressure reducing valve and a valve opening pressure of the pressure reducing valve when an abnormal increase is determined by the rail pressure abnormality increase determining means. The upper limit set pressure is corrected based on the fuel temperature correlation value detected by the fuel temperature correlation value detecting means, and the opening pressure of the pressure reducing valve is adjusted based on the corrected upper limit set pressure. The rail pressure control device for a common rail diesel engine according to any one of claims 1 to 4, wherein the rail pressure control device is controlled.

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