JP2007255362A - Fuel injection device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To maintain pressure control performance in low temperature areas and protect a system. <P>SOLUTION: In this fuel injection device for an internal combustion engine, the pressure of an accumulated fuel detected by a pressure sensor 7 is so controlled as to match an instruction pressure. An instruction pressure guard value is set based on the temperature of the pressure sensor 7. When the instruction pressure is equal to or more than the instruction pressure guard value, the instruction pressure is reduced to the instruction pressure guard value or below. The instruction pressure guard value when the temperature of the pressure sensor 7 is low is set lower than the instruction pressure guard value when the temperature of the pressure sensor 7 is high. By this, the pressure control performance can be maintained by reducing the effect of pressure deviation on the pressure sensor 7 in low temperature areas. Even when the output of the pressure sensor 7 is smaller than the actually accumulated fuel pressure in the low temperature areas, the system can be surely protected. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel injection device for an internal combustion engine that controls an accumulated fuel pressure so that the accumulated fuel pressure in the accumulator matches a command pressure.

  A conventional fuel injection device for an internal combustion engine detects an accumulated fuel pressure in an accumulator with a pressure sensor, calculates a command pressure of the accumulated fuel pressure based on an operating state of the internal combustion engine, and the accumulated fuel pressure becomes the command pressure. The accumulated fuel pressure is controlled so as to match (see, for example, Patent Document 1).

In recent years, with the tightening of exhaust gas regulations, increasing the pressure of accumulated pressure fuel (for example, 200 MPa or more) has been studied as one means for realizing this. In order to cope with this increase in pressure, pressure resistance performance of an accumulator, a pressure sensor and the like is being improved.
Japanese Patent No. 3058227

  However, as shown in FIGS. 7 and 8, a general pressure sensor has a characteristic that the pressure deviation (variation) increases as the temperature becomes lower and the pressure becomes higher. Therefore, the pressure controllability deteriorates in a low temperature and high pressure region where the pressure deviation is particularly large.

  Also, if the output of the pressure sensor is smaller than the actual accumulated fuel pressure, excessive pressure may be applied to the system (accumulator, pressure sensor, etc.), especially in the low temperature and high pressure region, and the system may not be protected. There is.

  An object of this invention is to provide the apparatus which can maintain the pressure controllability in a low temperature area | region and can protect a system in view of the said point.

  The present invention relates to a fuel injection device for an internal combustion engine that controls an accumulated fuel pressure so that an accumulated fuel pressure detected by a pressure sensor (7) matches a command pressure, based on the temperature of the pressure sensor (7). The pressure guard value is set, and when the command pressure is equal to or greater than the command pressure guard value, command pressure limiting means (S104 to S108) for limiting the command pressure to be equal to or less than the command pressure guard value is provided. -S108) are characterized in that the command pressure guard value is set to be lower when the temperature of the pressure sensor (7) is lower than when the temperature of the pressure sensor (7) is high.

  In this way, it is possible to maintain the pressure controllability by reducing the influence of the pressure deviation of the pressure sensor (7) in the low temperature region. Further, even when the output of the pressure sensor (7) is output smaller than the actual accumulated fuel pressure in the low temperature region, the system can be reliably protected.

  In this case, the command pressure limiting means (S104 to S108) can set the command pressure guard value low as the temperature of the pressure sensor (7) decreases.

  Further, the command pressure limiting means (S104 to S108) can set the command pressure guard value continuously low as the temperature of the pressure sensor (7) decreases.

  Further, the command pressure limiting means (S104 to S108) can set the command pressure guard value stepwise lower as the temperature of the pressure sensor (7) becomes lower.

      Furthermore, when the temperature of the pressure sensor (7) is in a certain temperature range, the command pressure limiting means (S104 to S108) continuously outputs the command pressure guard value as the temperature of the pressure sensor (7) decreases. When the temperature of the pressure sensor (7) is in another temperature range, the command pressure guard value can be set to a constant value.

  In addition, the code | symbol in the bracket | parenthesis of each means described in a claim and this column shows the correspondence with the specific means as described in embodiment mentioned later.

  An embodiment of the present invention will be described. FIG. 1 is a diagram showing an overall configuration of a fuel injection device for an internal combustion engine according to an embodiment of the present invention.

  An internal combustion engine (not shown) (more specifically, a diesel engine) provided with this fuel injection device is mounted on a vehicle (not shown). This fuel injection device includes a substantially cylindrical accumulator 1 for accumulating high-pressure fuel, and the accumulator 1 is connected to a plurality of fuel injection valves 2 provided for each cylinder of the internal combustion engine. The high pressure fuel accumulated in the vessel 1 is injected from each fuel injection valve 2 into the corresponding cylinder. The valve opening timing and valve opening time of the fuel injection valve 2 are controlled by an electronic control unit (hereinafter referred to as ECU) (not shown).

  The ECU includes a known microcomputer including a CPU, a ROM, a RAM, and the like, and sequentially executes various processes stored in the microcomputer. Then, the ECU receives information such as an output signal from an outside air temperature sensor 10 described later, an engine speed, and a depression amount of an accelerator pedal (not shown), and the ECU, based on the information, The operation of a pressure feed amount control valve 6 and a pressure reducing valve 9 to be described later is controlled.

  High pressure fuel is pumped from the fuel pump 3 to the accumulator 1, and the high pressure fuel is accumulated in the accumulator 1. As the fuel pump 3, a variable discharge high-pressure pump having a known structure is used, and the low-pressure fuel supplied from the fuel tank 4 serving as the low-pressure portion via the feed pump 5 is pressurized to a high pressure. The fuel pump 3 is provided with a pressure feed control valve 6 that controls the amount of low-pressure fuel supplied to the fuel pump 3.

  The pressure accumulator 1 is equipped with a pressure sensor 7 that detects the pressure of the fuel in the accumulator 1 (hereinafter referred to as a pressure accumulating fuel pressure). Then, the ECU calculates the command pressure of the accumulated fuel pressure based on the operating state of the internal combustion engine, and controls the accumulated fuel pressure so that the accumulated fuel pressure detected by the pressure sensor 7 matches the command pressure. Specifically, the pressure feed amount control valve 6 is driven to control the amount of low-pressure fuel supplied to the fuel pump 3, and thus the fuel pressure feed amount from the fuel pump 3 to the pressure accumulator 1 is controlled.

  The pressure accumulator 1 is connected to the fuel tank 4 via a leak pipe 8 that constitutes a discharge flow path. Further, a pressure reducing valve 9 that opens and closes the discharge flow path is attached to one end side in the longitudinal direction of the pressure accumulator 1. The pressure reducing valve 9 is controlled by the ECU in accordance with the operating state of the internal combustion engine, and when the valve is opened, the high pressure fuel in the pressure accumulator 1 is returned to the fuel tank 4 through the discharge flow path, whereby the accumulated fuel pressure is reduced to the target value. It is to reduce.

  Further, an outside air temperature sensor 10 for detecting the outside air temperature is provided. The outside air temperature sensor 10 corresponds to the temperature detecting means of the present invention.

  Next, a method for setting the command pressure in the pressure accumulation fuel pressure control for matching the pressure accumulation fuel pressure with the command pressure will be described. FIG. 2 is a flowchart showing a command pressure setting process in the pressure accumulation fuel pressure control executed by the ECU. This process is started when the ECU is turned on by operating the key switch, and is executed at a predetermined cycle, for example, until the power is turned off.

  As shown in FIG. 2, first, in step S101, the outside air temperature detected by the outside air temperature sensor 10 is read.

  Next, in step S102, a command pressure PFIN for the accumulated fuel pressure is obtained from a map stored in the ROM of the ECU based on the engine speed and the fuel injection amount. The command pressure PFIN for the accumulated fuel pressure increases as the engine speed increases, and increases as the fuel injection amount increases.

  Next, in step S103, a command pressure guard value PGRD for limiting the upper limit of the command pressure PFIN is obtained from a map stored in the ROM of the ECU based on the engine speed. The command pressure guard value PGRD increases as the engine speed increases.

  Next, in step S104, it is determined whether or not the temperature of the pressure sensor 7 is in a low temperature region. Specifically, the outside air temperature read in step S101 is regarded as the temperature of the pressure sensor 7, and if the outside air temperature is equal to or lower than the reference temperature, it is determined that the temperature of the pressure sensor 7 is in a low temperature region (step S104: YES). The process proceeds to step S105. Incidentally, the reference temperature is set to 0 ° C. in this embodiment.

  In step S105, a low temperature command pressure guard value PLOW for limiting the upper limit of the command pressure PFIN in the low temperature region is calculated based on the outside air temperature. This low temperature command pressure guard value PLOW is set lower than the command pressure guard value PGRD employed when the outside air temperature exceeds the reference temperature (0 ° C.).

  Here, a setting example of the low temperature command pressure guard value PLOW will be described. FIG. 3 is a diagram showing the relationship between the total pressure deviation of the pressure sensor 7 (that is, the sum of the pressure deviation shown in FIG. 7 and the pressure deviation shown in FIG. 8, the absolute value) and the temperature of the pressure sensor 7. , Line a is a pressure deviation when the actual pressure is 100 MPa, line b is a pressure deviation when the actual pressure is 180 MPa, and line c is a pressure deviation allowable in the system.

  The pressure satisfying the sum of the pressure deviations of the pressure sensor 7 ≦ the pressure deviation allowable in the system is the low temperature command pressure guard value PLOW, and the sum of the pressure deviations and the temperature of the pressure sensor 7 are in the relationship of FIG. In this case, the low temperature command pressure guard value PLOW is set as shown in FIG. Specifically, the low temperature command pressure guard value PLOW is set to continuously decrease as the temperature of the pressure sensor 7 decreases, in other words, as the outside air temperature decreases.

  Next, in step S106, the low temperature command pressure guard value PLOW is set as the value of the command pressure guard value PGRD.

  Next, in step S107, the command pressure PFIN is compared with the command pressure guard value PGRD set in step S106. If the command pressure PFIN is equal to or greater than the command pressure guard value PGRD (step S107: YES), the process proceeds to step S108.

  In step S108, the command pressure guard value PGRD set in step S106 is set as the command pressure PFIN. Then, the command pressure setting process is temporarily ended. Steps S104 to S108 constitute command pressure limiting means of the present invention.

  If NO is determined in step S107, that is, if the command pressure PFIN is less than the command pressure guard value PGRD, the command pressure setting process is temporarily ended without changing the command pressure PFIN.

  As described above, when it is determined that the temperature of the pressure sensor 7 is in the low temperature region (step S104: YES), the guard value of the command pressure PFIN is the value when the temperature of the pressure sensor 7 is in the middle / high temperature region. It is set lower than the guard value.

  In this way, it is possible to reduce the influence of the pressure deviation of the pressure sensor 7 in the low temperature region and maintain the controllability of the accumulated fuel pressure. Further, even when the output of the pressure sensor 7 is output smaller than the actual accumulated fuel pressure in the low temperature region, the system can be reliably protected.

  On the other hand, if NO is determined in step S104, that is, if the temperature of the pressure sensor 7 is in the middle / high temperature region, steps S105 and 106 are skipped and the process proceeds to step S107, so the command pressure guard value PGRD is set to step S103. The guard value obtained in the above is adopted.

(Other embodiments)
In the above embodiment, the outside air temperature is regarded as the temperature of the pressure sensor 7, and it is determined based on the outside air temperature whether the temperature of the pressure sensor 7 is in the low temperature region, and the low temperature command pressure guard value PLOW is determined as the outside air temperature. The temperature sensor for detecting the temperature of the fuel in the fuel pump 3 is provided, the fuel temperature detected by the temperature sensor is regarded as the temperature of the pressure sensor 7, and the temperature of the pressure sensor 7 is in the low temperature range. It may be determined whether or not there is a low temperature based on the fuel temperature, and the low temperature command pressure guard value PLOW may be calculated based on the fuel temperature.

  When both the outside air temperature sensor 10 and the temperature sensor for detecting the temperature of the fuel in the fuel pump 3 are provided, the temperature of the pressure sensor 7 is in the low temperature region when the outside air temperature and the fuel temperature are both lower than the reference temperature. You may make it determine.

  Further, the temperature of the pressure sensor 7 is estimated from the outside air temperature sensor 10 or a temperature sensor that detects the temperature of the fuel in the fuel pump 3, and when the estimated temperature is equal to or lower than the reference temperature, the temperature of the pressure sensor 7 is low. You may make it determine with there.

  In the above embodiment, when the temperature of the pressure sensor 7 is in the low temperature region, the guard value of the command pressure PFIN is continuously decreased as the temperature of the pressure sensor 7 is decreased. As shown in FIG. 5, the guard value of the command pressure PFIN may be decreased stepwise as the temperature of the pressure sensor 7 decreases.

  Alternatively, as shown in FIG. 6, when the temperature of the pressure sensor 7 is within a certain temperature range (0 ° C. to approximately −20 ° C. in this example), the command pressure is reduced as the temperature of the pressure sensor 7 decreases. The guard value of the command pressure PFIN may be fixed to a constant value in a region where the guard value of the PFIN is continuously lowered and the temperature is further lowered (approximately −20 ° C. or lower in this example).

  Further, contrary to the example of FIG. 6, when the temperature of the pressure sensor 7 is within a certain temperature range, the guard value of the command pressure PFIN is fixed to a certain value, and in the region where the temperature becomes lower, the temperature of the pressure sensor 7. As the value decreases, the guard value of the command pressure PFIN may be continuously decreased.

It is a figure showing the whole fuel injection device for internal-combustion engines concerning one embodiment of the present invention. It is a flowchart which shows the command pressure setting process performed with ECU. It is a figure which shows the relationship between the sum total of the pressure deviation of a pressure sensor, and the temperature of a pressure sensor. It is a figure which shows the example of a setting of the command pressure guard value at the time of low temperature. It is a figure which shows the other example of a setting of the command pressure guard value at the time of low temperature. It is a figure which shows the further another example of setting of the command pressure guard value at the time of low temperature. It is a figure which shows the relationship between the pressure deviation of a pressure sensor, and the temperature of a pressure sensor. It is a figure which shows the relationship between the pressure deviation of a pressure sensor, and an actual pressure.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Accumulator, ..., 7 ... Pressure sensor, 10 ... Outside temperature sensor.

Claims (5)

The pressure accumulation fuel pressure in the pressure accumulator (1) is detected by the pressure sensor (7), the command pressure of the pressure accumulation fuel pressure is calculated based on the operating state of the internal combustion engine, and the pressure accumulation fuel pressure matches the command pressure. In a fuel injection device for an internal combustion engine that controls an accumulated fuel pressure,
Temperature detection means (10) for detecting the temperature of the pressure sensor (7);
The command pressure guard value is set based on the temperature of the pressure sensor (7), and the command pressure is limited to the command pressure guard value or less when the command pressure is equal to or greater than the command pressure guard value. Means (S104 to S108),
The command pressure limiting means (S104 to S108) sets the command pressure guard value to be lower when the temperature of the pressure sensor (7) is higher than when the temperature of the pressure sensor (7) is low. A fuel injection device for an internal combustion engine, characterized by being set. The internal combustion engine according to claim 1, wherein the command pressure limiting means (S104 to S108) sets the command pressure guard value low as the temperature of the pressure sensor (7) decreases. Fuel injection device. The command pressure limiting means (S104 to S108) sets the command pressure guard value continuously low as the temperature of the pressure sensor (7) decreases. Fuel injection device for internal combustion engine. The said command pressure limiting means (S104-S108) sets the said command pressure guard value low stepwise as the temperature of the said pressure sensor (7) becomes low. Fuel injection device for internal combustion engine. When the temperature of the pressure sensor (7) is in a certain temperature range, the command pressure limiting means (S104 to S108) sets the command pressure guard value as the temperature of the pressure sensor (7) decreases. 3. The internal combustion engine for an internal combustion engine according to claim 2, wherein the command pressure guard value is set to a constant value when the pressure sensor (7) is in a different temperature range. Fuel injection device.

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