EP1726809A1

EP1726809A1 - Internal combustion engine with a plurality of cylinder pressure sensors per cylinder

Info

Publication number: EP1726809A1
Application number: EP06114164A
Authority: EP
Inventors: Ryo Suenaga
Original assignee: Denso Corp
Current assignee: Denso Corp
Priority date: 2005-05-19
Filing date: 2006-05-18
Publication date: 2006-11-29
Anticipated expiration: 2026-05-18
Also published as: DE602006014468D1; JP4148238B2; EP1726809B1; JP2006322402A

Abstract

A fuel injection system (5) for an engine (10) with a chamber (12) is disclosed. The fuel injection system (5) includes a plurality of pressure sensors (11) for detecting a plurality of pressure values within the chamber (12). The fuel injection system (5) also includes an ECU (20) that receives the plurality of pressure values detected by the plurality of pressure sensors (11). The ECU (20) generates a distribution of characteristic dispersion of a sensor simplex based on the plurality of pressure values detected by the plurality of pressure sensors (11). Also, the ECU (20) processes the distribution of characteristic dispersion to generate a distribution result that is within the distribution of characteristic dispersion. Moreover, the ECU (20) obtains a pressure result based on the distribution result.

Description

FIELD OF THE INVENTION

The present invention relates to a fuel injection system and, more particularly, relates to a fuel injection system that more accurately detects pressure based on pressure values from a plurality of pressure sensors.

BACKGROUND OF THE INVENTION

Fuel injection systems with fuel rails (i.e., "common rail type fuel injection systems" or "rail-type fuel injection systems") are known. In these systems, pressurized fuel accumulates within the fuel rail, and the fuel is supplied to an engine via a fuel injection valve.
Typically, a pressure sensor is included in this type of fuel injection system. The pressure sensor is used to detect a pressure value within the fuel rail, and feedback control of a fuel pump occurs to bring the fuel pressure in the fuel rail up to a target pressure. More specifically, the fuel injection system controls the amount of fuel pumped to the fuel rail according to the difference between the detected pressure value and the target fuel pressures.
In many cases, the pressure sensor exhibits a certain amount of error when detecting fuel pressure (i.e., the detected fuel pressure values have characteristic dispersion). The dispersion can detrimentally affect the performance of the engine.
Fuel injection systems have been proposed in partial response to this problem. For instance, Japanese Patent Application A-2003-161225 discloses a rail-type fuel injection system that includes a plurality of fuel pressure sensors. By including a plurality of fuel pressure sensors, the fuel pressure can be more accurately detected. Specifically, the fuel pressure sensors each individually detect a fuel pressure value, and these values are averaged in order to more accurately detect the fuel pressure within the system.
However, even in these systems, dispersion of the detected fuel pressure values may detrimentally affect the fuel injection performance. For instance, the dispersion may cause the detected fuel pressure value to be skewed negatively, such that the detected fuel pressure is too low. As a result, the fuel injection system may supply too much fuel to the fuel rail and damage the system. Conversely; the dispersion may cause the detected fuel pressure value to be skewed positively, such that the detected fuel pressure is too high. As a result, the fuel injection system may supply too little fuel to the fuel rail (e.g., when the engine is started, etc.).

SUMMARY OF THE INVENTION

Accordingly, a method of detecting pressure within a chamber of an engine is disclosed. The method includes detecting a plurality of pressure values of the chamber with a plurality of pressure sensors. The method also includes generating a distribution of characteristic dispersion of a sensor simplex based on the plurality of pressure values detected by the plurality of pressure sensors. In addition, the method includes processing the distribution of characteristic dispersion to generate a distribution result that is within the distribution of characteristic dispersion. Also, the method includes obtaining a pressure result based on the distribution result.
Furthermore, a fuel injection system for an engine with a chamber is disclosed. The fuel injection system includes a plurality of pressure sensors for detecting a plurality of pressure values within the chamber. The fuel injection system also includes an ECU that receives the plurality of pressure values detected by the plurality of pressure sensors. The ECU generates a distribution of characteristic dispersion of a sensor simplex based on the plurality of pressure values detected by the plurality of pressure sensors. Also, the ECU processes the distribution of characteristic dispersion to generate a distribution result that is within the distribution of characteristic dispersion. Moreover, the ECU obtains a pressure result based on the distribution result.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic illustration of one embodiment of a rail type fuel injection system disclosed herein;
Fig. 2 is a graphical illustration of results of operation of the fuel injection system of Fig. 1;
Fig. 3 is a graphical illustration of results of operation of the fuel injection system of Fig. 1;
Fig. 4 is a flow chart illustrating a method of operating the fuel injection system of Fig. 1;
Fig. 5 is a graphical illustration of results of operation of the fuel injection system of Fig. 1; and
Fig. 6 is a graphical illustration of results of operation of the fuel injection system of Fig. 1.

DETAILED DESCRIPTION

Fig. 1 schematically illustrates one embodiment of a rail-type fuel injection system 5 for an engine 10. In one embodiment, engine 10 is a diesel engine 10; however, it will be appreciated that the engine 10 could be of any suitable type.
As shown, the fuel injection system 5 includes a plurality of fuel injectors 11, such as electromagnetic-type fuel injectors 11. Each injector 11 is in communication with a cylinder of the engine 10, and supplies fuel thereto. The injectors 11 are also in communication with a chamber, such as a fuel rail 12 (i.e., an accumulating pressure pipe, etc.).
A pump 13 is in communication with the fuel rail 12. Fuel is accumulated in the fuel rail 12 in accordance with the operation of the high pressure pump 13. The pump 13 includes a suction metering valve 13 (SCV), such as an electromagnetic valve. Fuel is pumped from a fuel tank 15 by a feed pump 14 and moves into the pump 13 through the suction metering valve 13a.
In one embodiment, for example, the target fuel pressure within the fuel rail 12 is about 180 MPa, and the resisting pressure of the fuel rail 12 is about 200 MPa.
The fuel injection system 5 also includes a plurality of pressure sensors 16, 17. It will be appreciated that the fuel injection system 5 could include any number of pressure sensors 16, 17. The pressure sensors 16, 17 are each able to individually detect the fuel pressure (i.e., the pressure value) within the fuel rail 12. The pressure sensors 16, 17 then generate signals correlating to the detected pressure values.
Also, in one embodiment, the fuel injection system 5 includes a relief valve (not shown). The relief valve can be of any suitable type, such as an electromagnetic valve or a mechanical valve. When the detected fuel pressure value is too high, the relief valve is opened to thereby reduce the pressure within the fuel rail 12.
The fuel injection system 5 further includes an ECU 20. The ECU 20 is an electronic control unit having a known microcomputer with a CPU, ROM, RAM, EEPROM, etc. The ECU 20 is in communication with the pressure sensors 16, 17, and the ECU 20 receives the signals generated by the pressure sensors 16, 17. Then, by processing the signals in a manner to be described in greater detail below, the ECU 20 generates a "pressure result," which accurately correlates to the actual pressure within the fuel rail 12.
The ECU 20 also receives other signals from various sensors (not shown) in the engine 10, such as a rotating speed sensor, an acceleration aperture sensor, etc., to detect an operating condition of the engine 10. The ECU 20 also determines an appropriate target pressure value of the fuel rail 12 based on the particular operating condition of the engine 10. Then, ECU 20 feedback-controls the pump 13 to change the pressure within the fuel rail 12 such that the "pressure result" detected within the fuel rail 12 approximately equals the target pressure of the fuel rail 12. Thus, the fuel injection from the injectors 11 to the respective combustion chambers is controlled.
The operation of the ECU 20 will now be discussed in more detail. The pressure values detected by the pressure sensors 16, 17 are averaged. Each of the pressure sensors 16, 17 has characteristic dispersion such that the pressure values are dispersed by this characteristic dispersion. However, the dispersion of this common rail pressure can be statistically set to, for example, 1/√2 by averaging the two sensor detecting values.
Generally, if the number of sensors is N and the characteristic dispersion (i.e., allowance tolerance) of the sensor simplex is ±α, then the averaging processing is performed (i.e., the distribution of characteristic dispersion is generated and the districution result is generated) based on the detecting signal of each sensor 16, 17, and the characteristic dispersion statistically becomes ±α/√n. Accordingly, the dispersion amount is reduced, and the fuel injection system 5 is able to reduce detecting error.
As shown in Fig. 5, an example of the distribution of the characteristic dispersion in the sensor simplex is provided and labeled as the line P1. The distribution result generated by processing the distribution of characteristic dispersion is shown by a dotted line labeled P2. Accordingly, as represented in Fig. 5, the detecting accuracy of the fuel injection system 5 is improved over that of the prior art.
Also, in one embodiment, the distribution result is offset. In one embodiment, for instance, the distribution result is offset positively such that an upper limit of the distribution result is approximately equal to an upper limit of the distribution of characteristic dispersion. As such, it is unlikely that the calculated pressure result will be lower than the actual fuel pressure. Thus, it is unlikely that the fuel system will be overpressurized.
More specifically, as shown in Fig. 6, when the number of sensors is N and the characteristic dispersion (i.e., the allowance tolerance) of the sensor simplex is ±α [MPa], the difference between the upper limit value of the characteristic dispersion of the sensor simplex and the upper limit value of the distribution result is α-αl√N. Thus, the distribution result is correspondingly offset positively as shown by the line labeled P3 in Fig. 6.
Also, in one embodiment, the distribution result is offset negatively in the same manner. For instance, the distribution result is offset negatively such that a lower limit of the distribution result is approximately equal to the lower limit of the distribution of characteristic dispersion. As such, the distribution result can be offset negatively at engine start or at another suitable time. Accordingly, the rise in pressure of the fuel rail 12 will be hastened by offsetting the distribution result negatively, thereby improving fuel injection at the engine starting time or other suitable time.
Referring now to Fig. 2, another embodiment is illustrated having a dispersion of ±5 MPa as simplex characteristics. The solid line A in Fig. 2 shows the characteristic dispersion of the sensor simplex. The characteristic dispersion of the sensor simplex is distributed within the range of ±5 Mpa. Thus, the upper limit value is 5 MPa, and the lower limit value is -5 MPa.
When the averaging processing is executed (i.e., when the distribution result is generated), the dispersion statistically becomes: $\pm 5 / \sqrt{2} \approx \pm 3.5355 MPa$

As shown in Fig. 2, this distribution result is distributed as shown by a dotted line B, and the values of the upper and lower limits of the dispersion respectively become B1 = 3.5355 MPa and B2 = -3.5355 MPa. Thus, the dispersion amount can be reduced about 30 percent. The pressure result is obtained based on this distribution result, thereby allowing the fuel injection system 5 to detect pressure more accurately.
Also, when the averaging processing is executed by using three sensors, the dispersion after the averaging processing statistically becomes: $\pm 5 / \sqrt{3} \approx \pm 2.8868 MPa$

In Fig. 2, the dispersion result is distributed as shown by a two-dotted chain line (labeled C), and the values of the upper and lower limits of the dispersion result respectively become C1 = 2.8868 MPa and C2 = -2.8868 MPa. Thus, the dispersion amount can be reduced 40 percent or more. It will be appreciated that as the number of sensors is increased, the dispersion amount can be reduced, but its effect appears by a square root. Therefore, it is considered that a reducible ratio is gradually reduced.
Further, if dispersion occurs and the pressure result obtained by ECU 20 (i.e., the detected pressure of the fuel rail 12) is value lower than the actual pressure of the fuel rail 12, the ECU 20 may excessively raise the fuel pressure. This could negatively impact the operation of the engine 10 and/or cause damage to the fuel injection system 5.
Therefore, in one embodiment, the distribution result is offset positively. For instance, as shown in Fig. 3, the processing results of such a system are shown. In this embodiment, the fuel injection system 5 includes two pressure sensors 16, 17 having the dispersion of ±5 MPa as simplex characteristics. The characteristic dispersion of the sensor simplex is shown by a solid line labeled A', and the distribution result is shown by a dotted line labeled B'. The distribution result is offset positively as shown by a two-dotted chain line labeled B".
In the embodiment shown, the offset amount is "A1 - B1" at a maximum. Using the numerical values given above, the offset amount is: $5 - 3.5355 = 1.4645 MPa$

This is shown by the curve B" in Fig. 3. Also, the lower limit is shifted from point B2 to point X. Thus, X is expressed as: $X = - 3.5355 + 1.4645 = - 2.071 MPa$

Also, the upper limit value of the distribution result is approximately equal to the upper limit value of distribution of the characteristic dispersion.
In one embodiment, the maximum pressure usable in the system is be raised by the difference between point A2 and point X (e.g., 5 - 2.071 ≈ 2.9 MPa). The maximum pressure of the fuel rail 12 is controlled by the distribution result on the negative side due to feedback control. Thus, it is necessary to have a limit (i.e., a limit with respect to the resisting pressure) in the fuel rail maximum pressure in accordance with the dispersion amount on the negative side. In one embodiment, the limit of the fuel rail pressure is relaxed by changing the lower limit value of the distribution result as mentioned above (namely, by the changing B2 → X in Fig. 3) so that the maximum pressure is raised. Further, in this embodiment, the upper limit value of the distribution result on the positive side is not changed. Therefore, the system is more reliable. If the same margin degree is set, the usable pressure can be increased.
Fig. 4 is a flow chart showing the method of operating the fuel injection system 5. The ECU 20 repeatedly executes this method of operation in a predetermined angle period (or time period).
As shown in Fig. 4, the method begins in step S101, in which the ECU 20 receives the plurality of pressure values (e.g., A/D values) detected by the pressure sensors 16, 17. Then, in step S102, the ECU 20 generates and processes the distribution of characteristic dispersion to thereby generate the distribution result as described above.
Next, in step S103, the distribution result is offset either positively or negatively as described above. In one embodiment, the offset amount is "α-α/√N" when the tolerance of one side of the simplex dispersion is ±α and the number of used common rail pressure sensors is N. Thus, if α is equal to 5 MPa and N is equal to 2, the offset amount is equal to approximately: $5 - 5 / \sqrt{2} = 1.4645$

Thus, the distribution result is offset by this amount, and the pressure result obtained is based on the offset distribution result.
Thereafter, in step S104, a target pressure of the fuel rail 12 is determined according to the current operating condition of the engine. In one embodiment, the ECU 20 references one or more look-up tables to thereby determine the target pressure of the fuel rail 12. Then, in step S105, the ECU 20 feedback controls the fuel pump 13 such that the pressure result approximately equals the target pressure.
Accordingly, the accuracy of the fuel injection amount of the injector 11 can be improved due to the improved pressure detecting accuracy of the fuel injection system 5. Furthermore, the maximum pressure of the fuel rail 12 can be increased without reducing the operating life of the fuel injection system 5.
As mentioned above, an allowance level of the characteristic dispersion can be relaxed as the sensor simplex by improving the detecting accuracy of the common rail pressure by averaging the plurality of pressure values detected by the pressure sensors 16, 17. Therefore, a reduction in yield of the common rail pressure sensor can be restrained.
Furthermore, the distribution result can be offset such that the upper limit value of the distribution result is approximately equal to an upper limit of the distribution of characteristic dispersion. However, it will be appreciated that the distribution result could be offset such that the upper limit values are not equal. For example, in one embodiment, the distribution result is offset such that the upper limit value of the distribution result is less than the upper limit of the distribution of characteristic dispersion. In such a case, the detecting accuracy of the fuel injection system 5 can be improved and the maximum pressure of the fuel rail 12 can be increased.
Moreover, when the pressure of the fuel rail 12 is raised (e.g., at an engine starting time), the detected pressure values obtained from the pressure sensors 16, 17 may exceed the actual pressure of the fuel rail 12, and the fuel pressure may not be raised quickly enough. Thus, as described above, the distribution result can be offset negatively at engine start or at another suitable time. Accordingly, the rise in pressure of the fuel rail 12 will be hastened by offsetting the distribution result negatively, thereby improving fuel injection at the engine starting time or other suitable time.
Also, in one embodiment, it is possible to switch whether or not the distribution result is offset based on the operating state of the engine 10, etc. Further, it is possible to switch whether the distribution result is offset positively or offset negatively based on the operating state of the engine 10, etc.
The present invention has been described in an illustrative manner. It is to be understood that the terminology, which has been used, is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings. Therefore, within the scope of the appended claims, the present invention may be practiced other than as specifically described.
A fuel injection system (5) for an engine (10) with a chamber (12) is disclosed. The fuel injection system (5) includes a plurality of pressure sensors (11) for detecting a plurality of pressure values within the chamber (12). The fuel injection system (5) also includes an ECU (20) that receives the plurality of pressure values detected by the plurality of pressure sensors (11). The ECU (20) generates a distribution of characteristic dispersion of a sensor simplex based on the plurality of pressure values detected by the plurality of pressure sensors (11). Also, the ECU (20) processes the distribution of characteristic dispersion to generate a distribution result that is within the distribution of characteristic dispersion. Moreover, the ECU (20) obtains a pressure result based on the distribution result.

Claims

A method of detecting pressure within a chamber (12) of an engine (10) comprising:
detecting a plurality of pressure values of the chamber (12) with a plurality of pressure sensors (11);

generating a distribution of characteristic dispersion of a sensor simplex based on the plurality of pressure values detected by the plurality of pressure sensors (11);

processing the distribution of characteristic dispersion to generate a distribution result that is within the distribution of characteristic dispersion; and

obtaining a pressure result based on the distribution result.
The method of claim 1, further comprising:
determining a target pressure of the chamber (12); and

feedback controlling a fuel pump (13) to change pressure within the chamber (12) such that the pressure result approximately equals the target pressure.
The method of claim 1, wherein a count of the plurality of pressure sensors (11) is N, wherein the characteristic dispersion is ±α, and wherein processing the distribution comprises creating a distribution result that satisfies ±α/√N.
The method of claim 1, further comprising offsetting the distribution result, and wherein the step of obtaining the pressure result comprises obtaining the pressure result based on the offset distribution result.
The method of claim 4, wherein offsetting the distribution result comprises offsetting the distribution result positively such that an upper limit of the distribution result is approximately equal to an upper limit of the distribution of characteristic dispersion.
The method of claim 4, wherein offsetting the distribution result comprises offsetting the distribution result negatively such that a lower limit of the distribution result is approximately equal to a lower limit of the distribution of characteristic dispersion.
The method of claim 4, wherein a count of the plurality of pressure sensors (11) is N, wherein the characteristic dispersion is ±α, and wherein offsetting the result satisfies α - α/√N.
A fuel injection system (5) for an engine (10) with a chamber (12), the fuel injection system (5) comprising:
a plurality of pressure sensors (11) for detecting a plurality of pressure values within the chamber (12); and

an ECU (20) that receives the plurality of pressure values detected by the plurality of pressure sensors (11), wherein:
the ECU (20) generates a distribution of characteristic dispersion of a sensor simplex based on the plurality of pressure values detected by the plurality of pressure sensors (11);

wherein the ECU (20) processes the distribution of characteristic dispersion to generate a distribution result that is within the distribution of characteristic dispersion; and

wherein the ECU (20) obtains a pressure result based on the distribution result.
The fuel injection system (5) of claim 8, wherein the engine (10) further comprises a fuel pump (13) that supplies fuel to the chamber (12), wherein the ECU (20) determines a target pressure of the chamber (12), and wherein the ECU (20) feedback controls the fuel pump (13) to change pressure within the chamber (12) such that the pressure result approximately equals the target pressure.
The fuel injection system (5) of claim 8, wherein a count of the plurality of pressure sensors (11) is N, wherein the characteristic dispersion is ±α, and wherein the ECU (20) processes the distribution of characteristic dispersion to generate a distribution result that satisfies ±α/√N.
The fuel injection system (5) of claim 8, wherein the ECU (20) offsets the distribution result, and the ECU (20) obtains the pressure result based on the offset distribution result.
The fuel injection system (5) of claim 11, wherein the ECU (20) offsets the distribution result positively such that an upper limit of the distribution result is approximately equal to an upper limit of the distribution of characteristic dispersion.
The fuel injection system (5) of claim 11, wherein the ECU (20) offsets the distribution result negatively such that a lower limit of the distribution result is approximately equal to a lower limit of the distribution of characteristic dispersion.
The fuel injection system (5) of claim 11, wherein a count of the plurality of pressure sensors (11) is N, wherein the characteristic dispersion is ±α, and wherein the ECU (20) offsets the distribution result so as to satisfy α - α/√N.