JPH109073A - Property learning device for fuel pressure sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the accuracy of a fuel pressure sensor, and improve the engine starting performance. SOLUTION: The detected value MPSS and engine speed Ne of a fuel pressure sensor detecting the delivery pressure of a high pressure fuel pump, are read in (S1), the value MPSS detected is stored as MPL when the engine speed Ne after 50ms has elapsed since a low pressure fuel pump was driven, is in an almost suspended condition, and the value MPSS when the engine speed Ne is greater than an idling engine speed Ni, is also stored as MPH (S2 through S5, S7 to S8), based on both respective values MPML and MPMH after averaging has been processed and set values PL and PH having been adjusted by a low and a high pressure regulator when they were detected, a property formula is set up (S6 and S9 to S10) which indicates the relation of actual fuel pressure PSS with respect to the detected value MPSS.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge pressure of a high pressure fuel pump for correcting a fuel injection amount at the time of starting in a spark ignition direct injection type engine or the like in which fuel discharged by a high pressure fuel pump is directly injected into a combustion chamber. TECHNICAL FIELD The present invention relates to a technique for compensating detection accuracy of a fuel pressure sensor that detects a pressure.

[0002]

2. Description of the Related Art In recent years, in a spark ignition type engine such as a gasoline engine, research has been conducted on a system in which an injection hole of a fuel injection valve is installed facing a combustion chamber and fuel is directly injected into the combustion chamber by the fuel injection valve. According to the spark ignition type direct injection internal combustion engine, compared to a premixed spark ignition engine having a fuel injection valve at an intake port, the transient operation characteristics are deteriorated due to fuel transport delay and the exhaust gas composition is reduced. There is an advantage that the deterioration of can be suppressed.

In this type of engine, a high-pressure fuel pump is provided in the middle of a fuel supply passage as a method for increasing the fuel injection pressure in order to enhance the atomization effect of the fuel (Japanese Patent Laid-Open No. Hei 5 (1993)).
-321783 etc.).

[0004]

In the high-pressure fuel pump of the internal combustion engine, the fuel pressure does not increase to the pressure adjusted by the pressure regulator at the time of starting, and the fuel injection amount control according to the adjusted pressure does not increase the fuel pressure. Insufficient injection volume. For this reason, it has been considered to control the fuel injection amount by detecting the fuel pressure with a fuel pressure sensor and correcting the injection time (pulse width) of the fuel injection valve with the fuel pressure.

However, the region where the fuel pressure at the time of starting is low is a region where the accuracy of the fuel pressure sensor is originally poor, so that there is a problem that the accuracy cannot be obtained by correcting the fuel injection amount based on the detection value of the fuel pressure sensor. . That is, since a fuel pressure sensor generally has a full-scale error (offset error),
As shown in FIG. 4, the error increases as the pressure decreases. For example, when the pressure value regulated by the high pressure regulator 16 is 5 MPa,
An error of 3% results in an error of ± 30% at a low pressure of 0.3 MPa regulated by the low-pressure regulator 13 immediately after starting or the like.

[0006] The discharge pressure of a high-pressure pump such as a direct injection engine, when the pump rotation speed is sufficiently increased (300 to 500 rpm or more), is determined by an upper limit pressure (5 to 8M) determined by a pressure regulator.
(Pa), the fuel pressure is determined with high accuracy by the pressure regulator. However, as described above, the fuel pressure does not increase to the upper limit pressure of the pressure regulator at the start of rotation at the time of starting, etc. If an attempt is made to use the values, the accuracy is not obtained because of the influence of the above error. Further, if a fuel pressure sensor that can obtain high accuracy even at a low pressure is used, the cost increases.

SUMMARY OF THE INVENTION The present invention has been made in view of such a conventional problem. By learning using a pressure regulator to compensate for the accuracy of a fuel pressure sensor, the initial performance is not so high and the cost is low. It is an object of the present invention to enable a fuel pressure to be detected with sufficiently high accuracy even when a fuel pressure sensor is used. It is another object of the present invention to improve the starting performance by compensating the accuracy of the fuel pressure sensor to increase the accuracy of correcting the fuel injection amount at the time of starting.

[0008]

Therefore, according to the first aspect of the present invention, as shown in FIG. 1, a low-pressure fuel pump for discharging fuel at a relatively low pressure and a low-pressure fuel pump discharged from the low-pressure fuel pump are provided. A high-pressure fuel pump that draws in fuel and discharges the fuel at a relatively high pressure; a low-pressure regulator that adjusts the fuel pressure when the discharge fuel pressure from the low-pressure fuel pump is sufficiently increased to a low-pressure set value; A high-pressure regulator that adjusts the fuel pressure when the fuel pressure discharged from the fuel pump is sufficiently increased to a high-pressure set value, and supplies fuel whose fuel pressure has been adjusted by the high-pressure regulator to the engine by a fuel injection valve, A fuel pressure sensor for detecting a fuel pressure discharged from the fuel pump for fuel, a fuel pressure sensor for detecting a rising fuel pressure of the high-pressure fuel pump, and correcting a fuel injection amount based on the detected fuel pressure. In the fuel system of the internal combustion engine provided with the injection amount correcting means, when the discharge pressure of the low-pressure fuel pump is sufficiently increased and the high-pressure fuel pump is substantially in a non-driving state, the detection of the fuel pressure sensor is performed. A value corresponding to a low pressure set value adjusted by the low pressure regulator, and a detection value of the fuel pressure sensor when the discharge pressure of the high pressure fuel pump is sufficiently increased is set to a high pressure adjusted by the high pressure regulator. A sensor characteristic learning means for performing learning corresponding to the values and learning the relationship between the detected value of the fuel pressure sensor and the actual fuel pressure based on the two detected values and the set values. It is characterized by.

(Operation / Effect) After the engine is started, the discharge pressure of the low-pressure fuel pump rises sufficiently to reach the low-pressure set value adjusted by the low-pressure regulator. When in the non-drive state, the fuel pressure is adjusted to a low pressure set value by the low pressure regulator.

Therefore, learning is performed to make the value detected by the fuel pressure sensor in the above state correspond to the adjusted set value for low pressure. After the discharge pressure of the high-pressure fuel pump has sufficiently increased, the fuel pressure is adjusted to a high-pressure set value by the high-pressure regulator. Therefore, learning is performed to make the value detected by the fuel pressure sensor correspond to the adjusted set value for high pressure in the above state.

Since the characteristic variation of the fuel pressure sensor is mainly due to an offset error and the linearity is extremely good, the detected value of the fuel pressure sensor is determined based on the learned value and the set value of the fuel pressure sensor at the two points. And the actual fuel pressure can be learned, the fuel pressure can be accurately detected based on the learned characteristics of the fuel pressure sensor, and the starting performance can be improved by improving the correction accuracy of the fuel injection amount. Can be.

Further, the invention according to claim 2 is characterized in that the low-pressure fuel pump is electrically driven, and the high-pressure fuel pump is driven by an engine. (Operation / Effect) Since the low-pressure fuel pump is electrically driven,
It has the characteristic that the discharge pressure rises quickly after the N operation, but it is difficult to secure large electric power for vehicles and the like, so it is used as a low-pressure fuel pump with a low maximum discharge pressure.

On the other hand, since the high-pressure fuel pump is of an engine driven type, there is a large delay in increasing the discharge pressure after the engine is started.
Used as a high-pressure fuel pump because a large maximum discharge pressure can be obtained. In the invention according to claim 3, the condition for making the detection value of the fuel pressure sensor correspond to a low pressure set value adjusted by the low pressure regulator is such that the electric low pressure fuel pump is in an ON state, and The engine speed is lower than a predetermined low speed.

(Operation / Effect) As described above, after the ON operation of the electric low-pressure fuel pump, the discharge pressure rapidly increases,
Since the discharge pressure of the engine-driven high-pressure fuel pump does not increase when the engine speed is low, the fuel pressure is regulated to the low-pressure set value. Therefore, in this state, the accuracy on the low pressure side is ensured by performing learning to make the detection value of the fuel pressure sensor correspond to the set value for low pressure.

Further, the invention according to claim 4 is characterized in that the fuel injection valve directly injects fuel into a combustion chamber of a spark ignition type engine. (Operation / Effect) As described above, in an engine that directly injects fuel into the combustion chamber, the fuel injection pressure must be sufficiently high.
Accordingly, it is necessary to sufficiently increase the discharge pressure of the high-pressure fuel pump, so that a delay in the rise of the discharge pressure tends to be prolonged. The effect is great, and the effect of improving startability is high.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 shows an overall system configuration according to an embodiment of the present invention. In FIG. 2, an engine 1 has an electromagnetic fuel injection valve 2 arranged with its injection hole facing the combustion chamber 3, and suctioned into the combustion chamber 3 via an intake port 4 and an intake valve 5. This is a spark-ignition direct-injection engine in which fuel is injected from the fuel injection valve 2 to form air-fuel mixture, and the air-fuel mixture is ignited by spark ignition by a spark plug 6.

The exhaust gas of the engine 1 is discharged from the fuel chamber 3 through an exhaust valve 7 and an exhaust port 8, and is discharged into the atmosphere through an exhaust purification catalyst and a muffler (not shown). The fuel in the fuel tank 9 is discharged at a relatively low pressure by an electric low-pressure fuel pump 10 and the low-pressure side fuel passage 11
After being filtered by the filter 12 interposed in A, the fuel pressure is adjusted to a constant low-pressure set value, for example, 0.3 MPa by a low-pressure regulator 13 provided in the low-pressure fuel passage 11B downstream of the filter 12 by bypass. The discharged fuel is sent to a high-pressure fuel pump 14 for high pressure.

The high-pressure fuel pump 14 for high pressure is driven directly by the crankshaft or camshaft of the engine 1 or indirectly via gears or belts, and pressurizes and discharges the low-pressure fuel to a high pressure. The fuel discharged from the high-pressure pump 14 is:
The high pressure regulator 16 provided in the high pressure side fuel passage 15 bypasses the high pressure fuel passage 15 so that the fuel pressure is constant at a high pressure set value, for example, 5M.
It is adjusted to Pa.

The fuel injection valve 2 is controlled to open in response to a pulse signal of a predetermined width corresponding to the engine operating state sent from the control unit 17 containing a microcomputer at a predetermined injection timing to adjust the fuel pressure to the predetermined fuel pressure. The fuel thus injected is injected into the combustion chamber 3. The control unit 17 is provided for detecting the engine rotational speed for the fuel injection control, and for controlling the fuel injection.
Detection signals from various sensors, such as a crank angle sensor 18 also for detecting the rotation speed of the air, an air flow meter 19 for detecting the intake air flow rate, and a fuel pressure sensor 20 for detecting the fuel pressure in the high-pressure side fuel passage 15 are input. It has become.

Here, the control unit 17 controls the pulse width of the injection pulse signal, and starts the output of the injection pulse signal, that is, the fuel injection valve 2.
Controls the fuel injection period. As described above, after the start, while the increase in the discharge pressure of the high-pressure fuel pump 14 is delayed, the fuel injection period of the fuel injection valve 2 is corrected by the fuel pressure detected by the fuel pressure sensor 20.

A detection characteristic learning routine of the fuel pressure sensor 20 by the control unit 9 will be described. This routine constitutes the sensor characteristic learning means. FIG.
Shows the state of the engine rotational speed Ne and the fuel pressure in the high-pressure side fuel passage 15 after the start, and an electric low-pressure fuel pump
While the discharge pressure of 10 rises immediately after the ON operation,
High-pressure setting value slower the engine speed Ne is increased in the discharge pressure of the high pressure fuel pump 14 is the fuel pressure from when a predetermined idle rotational speed Ni or is restricted by the high pressure regulator 16 P _H
(For example, 5 MPa). A description will be given according to the flowchart of FIG. 3 with reference to FIG.

Step (S in the figure; the same applies hereinafter) 1
Then, the detection value of the fuel pressure sensor 20 is A / D converted and MP
In addition to reading as ss, the engine rotation speed Ne calculated based on the signal from the crank angle sensor 18 is read. In step 2, the electric low-pressure fuel pump 10
It is determined whether or not N is set.

When it is determined that the low-pressure fuel pump 10 is ON, the routine proceeds to step 3, where the low-pressure fuel pump 10 is turned on.
After the ON operation of 10, the process proceeds to step 4 after a lapse of a set time, for example, 50 ms. When the set time has elapsed, the discharge pressure from the low-pressure fuel pump 10 is sufficiently increased,
The set time is set so as to be adjusted to the set value for low pressure regulated by the regulator for low pressure.

In step 4, the engine speed Ne is set to approximately 0
That is, it is determined whether or not the vehicle is substantially stopped. This determination is to determine whether the discharge pressure is less than the low pressure set value while the high pressure fuel pump 14 is in a substantially non-driven state.
Therefore, the determination condition may be that the engine speed is equal to or lower than the engine speed _NL set to a low speed so that this condition is satisfied.

If it is determined in step 4 that the engine is substantially stopped, that is, if it is determined that the fuel pressure is being adjusted to a constant low pressure set value (see FIG. 4a), the process proceeds to step 5. storing the detected value MPss of the fuel pressure sensor 20 read in step 1 as the value MP _L corresponding to the set value P _L for the low pressure. In step 6, the MP _L
Is averaged by a weighted average or the like, and the low-pressure side learning value _MPML is obtained.

On the other hand, if it is determined in step 4 that the engine is rotating, the routine proceeds to step 7, where the engine speed Ne is determined.
Is greater than or equal to a predetermined idle speed Ni.
If it is determined that Ne ≧ Ni, it is determined that the discharge pressure of the high-pressure fuel pump 14 has been sufficiently increased and adjusted to the high-pressure set value (see FIG. 4B). storing the detected value MPss of the fuel pressure sensor 20 as a value MP _H corresponding to the high-pressure setting value.

[0027] In step 9, the high-pressure side learning value MP _MH latest value and the value of the past multiple times of the MP _L and averaging process by a weighted average or the like. In step 10, the detected value MPss detected by the current fuel pressure sensor 20, the low-pressure side learning value MP _ML corresponding thereto and low pressure set value P _L, a high-pressure setting value P _H
And based on by the high-pressure side learning value MP _MH correspondence thereto, the characteristic equation for calculating the actual fuel pressure Pss corresponding to the detection value MPss of the fuel pressure sensor 20 are set as follows.

Pss = P _L + (P _H −P _L ) · (MPss−
_{MP ML) / (MP MH -MP} ML) For example, P _L = 0.3 MPa, in the case of _{P H = 5.0 MPa, Pss =} 0.3 +4.7 × (MPss-MP ML) / (MP MH -M
P _ML ) [MPa]. That is, since the offset error is the main cause of the deterioration of the accuracy of the fuel pressure sensor, as shown in FIG. 5, the detected value MPss of the fuel pressure sensor 20 in a state where the actual fuel pressure is adjusted to P _L and P _H is shown. Vary, but their detected values
If (output voltage) is learned, the linearity of the output characteristic of the fuel pressure sensor during that period, that is, the characteristic in which the sensor output changes proportionally to the change in fuel pressure, is good. It is possible to accurately detect the fuel pressure of the discharge pressure of the high-pressure fuel pump after the start until the fuel pressure rises from the low-pressure set value to the high-pressure set value.

FIG. 6 shows a flowchart of a routine for correcting the fuel injection amount at the start and immediately after the start. This routine constitutes the fuel injection amount correction means. In step 11, the detected value MPss of the fuel pressure detected by the fuel pressure sensor 20
Read. In step 12, the fuel pressure Pss is calculated from the detected value MPss of the fuel pressure sensor 20 and the characteristic equation of the fuel pressure sensor set in FIG.

In step 13, the calculated fuel pressure Pss is
It is determined whether or not the value is lower than the high pressure set value P _H (= 5 MPa). Pss <When it is determined that the P _H Step 14
Then, the correction coefficient k of the fuel injection amount is calculated by the following equation. k = In (P _H / Pss) ^1/2 Step 15, the fuel injection amount T _I at the start, is calculated by the following equation.

T _I = Te × k + Ts Here, Te is an effective injection pulse width when fuel is injected with the fuel pressure adjusted to the high pressure set value P _H , and Ts corresponds to the battery voltage. Invalid injection pulse width. Further, the process proceeds to step 16 when it is determined that Pss ≒ P _H in step 13, without performing correction by the fuel pressure, and calculates the fuel injection amount T _I by the following equation.

T _I = Te + Ts In this way, even if an inexpensive fuel pressure sensor that is not so accurate is used, the fuel pressure can be detected with high accuracy by performing learning using the adjustment value of the pressure regulator. Accordingly, the fuel injection amount can be accurately corrected based on the fuel pressure when the discharge pressure of the high-pressure fuel pump is increasing immediately after the start and immediately after the start, so that the starting performance can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration and functions of the present invention.

FIG. 2 is a diagram showing an overall system configuration according to an embodiment of the present invention.

FIG. 3 is a flowchart showing a routine for learning characteristics of a fuel pressure sensor in the embodiment.

FIG. 4 is a time chart showing the relationship between the engine speed and the fuel pressure at the time of starting the engine and immediately after the starting.

FIG. 5 is a diagram showing a relationship between a detection value of a fuel pressure sensor and an actual fuel pressure.

FIG. 6 is a flowchart showing a routine for setting a fuel injection amount.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Fuel injection valve 3 Combustion chamber 9 Fuel tank 10 Low pressure fuel pump 13 Low pressure regulator 16 High pressure fuel pump 15 High pressure regulator 17 Control unit 20 Fuel pressure sensor

Claims (4)

[Claims] A low-pressure fuel pump for discharging fuel at a relatively low pressure; a high-pressure fuel pump for sucking fuel discharged from the low-pressure fuel pump and discharging at a relatively high pressure; A low pressure regulator that adjusts the fuel pressure when the fuel pressure discharged from the fuel pump is sufficiently increased to a low pressure set value, and a fuel pressure when the fuel pressure discharged from the high pressure fuel pump is sufficiently increased is adjusted to a high pressure set value. A high-pressure regulator, and a fuel pressure sensor that detects fuel pressure discharged from the high-pressure fuel pump while supplying fuel whose fuel pressure has been adjusted by the high-pressure regulator to an engine through a fuel injection valve; A low-pressure fuel in an internal combustion engine fuel system comprising a fuel injection amount correcting means for detecting a discharge fuel pressure during the rise of the fuel pressure and correcting the fuel injection amount based on the detected fuel pressure. When the discharge pressure of the pump is sufficiently increased, and the high-pressure fuel pump is substantially in a non-driving state, the detection value of the fuel pressure sensor is made to correspond to the low-pressure set value adjusted by the low-pressure regulator, Learning is performed to make the detected value of the fuel pressure sensor when the discharge pressure of the high-pressure fuel pump sufficiently rises correspond to the high-pressure set value adjusted by the high-pressure regulator, and the learned detection values of the two points are A characteristic learning device for a fuel pressure sensor, comprising: sensor characteristic learning means for learning a relationship between a detected value of the fuel pressure sensor and an actual fuel pressure based on each set value. 2. The characteristic learning device for a fuel pressure sensor according to claim 1, wherein the low-pressure fuel pump is electrically driven, and the high-pressure fuel pump is driven by an engine. 3. A condition for making the detection value of the fuel pressure sensor correspond to a low pressure set value adjusted by the low pressure regulator is such that the electric low pressure fuel pump is in an ON state and the engine speed is low. 3. The characteristic learning device for a fuel pressure sensor according to claim 2, wherein the low-speed state is less than a predetermined value. 4. The fuel pump for an internal combustion engine according to claim 1, wherein said fuel injection valve directly injects fuel into a combustion chamber of a spark ignition type engine. Discharge amount estimation device.