JP4877189B2 - Fuel injection system - Google Patents

Description

  The present invention relates to a fuel injection control device that injects fuel directly into a combustion chamber of an internal combustion engine and in a plurality of times for one combustion.

  Sensors are attached to the internal combustion engine, that is, the engine, and the ECU controls the amount of fuel injected by the fuel injection device and the ignition timing according to information from the sensors.

In order to cope with individual differences and deterioration with time of the fuel injection device and the sensor, the variation in the measured value and the fuel injection amount by the sensor is learned, and the fuel injection amount and the injection period are corrected using the learning value obtained thereby. The configuration is known (Patent Document 1).
JP 2001-98991 A

  However, if individual differences and deterioration with time of the fuel injection device and the sensor increase, there is a possibility that the range that can be corrected by the learning value is exceeded. In this case, the fuel injection device cannot be properly controlled, a desired air-fuel ratio cannot be obtained, the emission may be deteriorated, and the engine may not exhibit a predetermined performance.

  The present invention has been made in view of this problem, and even if the individual difference and deterioration with time of the fuel injection device and sensor increase, the fuel injection system that suppresses the deterioration of the emission and exhibits the predetermined performance of the engine. And to get the engine.

  A fuel injection system according to a first invention of the present application is an air-fuel ratio measuring means attached to an exhaust system of an internal combustion engine, and a fuel that injects fuel directly into a combustion chamber of the internal combustion engine and divided into a predetermined number of times per combustion. Injection means, and a learning value calculation means for calculating a learning value used to correct the fuel injection amount so as to reduce the air-fuel ratio error between the target air-fuel ratio and the actual air-fuel ratio measured by the air-fuel ratio measuring means, The fuel injection means reduces the predetermined number of times when the learned value deviates from a normal range. The fuel injection means injects the fuel a plurality of times in any one or a plurality of strokes from the intake stroke to the exhaust stroke of the internal combustion engine. When fuel is injected divided into a predetermined number of times, the individual difference of the fuel injection device and the sensor and the error of the fuel injection amount due to deterioration with time increase, but according to the first invention of this application, the individual of the fuel injection device and the like Even if the difference and the deterioration with time increase, it is possible to suppress the deterioration of the engine emission and obtain a predetermined performance.

  The fuel injection means preferably sets the predetermined number of times once when the learning value exceeds a specified value. It is possible to minimize errors in the fuel injection amount due to individual differences in fuel injection devices and sensors and deterioration with time, to suppress deterioration in engine emissions, and to ensure that predetermined performance is obtained.

  A spark ignition direct injection internal combustion engine according to a second invention of the present application is characterized by comprising the above fuel injection system. As a result, a spark ignition type direct injection internal combustion engine capable of suppressing deterioration of engine emission and exhibiting predetermined performance even when individual differences and deterioration with time of the fuel injection device and sensor become large is obtained. Can do.

  According to the present invention, a fuel injection system and an engine in which deterioration of engine emission is suppressed and the engine exhibits predetermined performance even when the individual difference and deterioration with time of the fuel injection device and sensor increase are obtained.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a view showing a spark ignition direct injection internal combustion engine (hereinafter referred to as an engine) to which an embodiment of a fuel injection system according to the present invention is applied.

  Air sucked through the air cleaner 131 is sucked into a combustion chamber 141 formed in the engine 110 main body. An air flow meter 134 is attached to the air cleaner 131, and the air flow rate is measured and transmitted to the ECU 112. Fuel is injected from the fuel injection device 111 into the combustion chamber 141. Air is mixed with fuel in the combustion chamber 141. A spark plug 142 is provided at the top of the combustion chamber 141 and ignites the fuel / air mixture in accordance with a signal from the ECU 112. After the air-fuel mixture burns, it becomes exhaust gas and is discharged to the exhaust pipe 151. The exhaust gas is purified by the catalyst 152 and then released to the atmosphere. An A / F sensor 113 is attached to the exhaust pipe 151, detects the air-fuel ratio from the exhaust gas, and transmits it to the ECU.

  Fuel is injected into the common rail 115 by a fuel pump 114 from a fuel tank (not shown) and pressurized. The common rail 115 and the fuel injection device 111 are connected by a fuel pipe 116, and pressurized fuel is supplied to the fuel injection device 111. A fuel pressure sensor 117 for measuring the fuel pressure accumulated in the common rail 115, that is, a fuel pressure, is attached to the common rail 115, and the fuel pressure value is transmitted to the ECU 112.

  The fuel injection device 111 is provided such that the injection port 118 protrudes from the cylinder head 143 that constitutes the combustion chamber 141. An opening / closing valve 120 is provided inside the injection port 118, and fuel is injected into the combustion chamber 141 by opening / closing the opening / closing valve 120. An EDU (injector drive unit) 119 is connected to the fuel injection device 111. The EDU 119 energizes the fuel injection device 111 in accordance with the fuel injection signal from the ECU 112. The fuel injection device 111 injects fuel for the energization time during which power is supplied from the EDU 119. The fuel injection device 111 performs multi-injection. The multi-injection is to inject fuel a plurality of times in any one of the strokes from the intake stroke to the exhaust stroke of the engine 110. By performing multi-injection when the engine is operating at a high load, the homogeneity of the fuel in the combustion chamber is improved. For example, fuel is injected at BTDC 320 °, 300 °, 280 °.

  Since the on-off valve 120 provided in the fuel injection device 111 is mechanically operated, for example, is constituted by a solenoid valve, it requires a valve transition period from a completely closed state to a fully opened state or vice versa. . Since this valve transition period occupies a non-negligible ratio relative to the opening period from when the on-off valve 120 starts to open until it completely closes, there is a time lag between the energization period of the fuel injection device 111 and the actual fuel injection period. Occurs. Furthermore, since it is physically impossible for the on-off valve 120 to open and close completely following energization, the energization start timing, the on-off valve 120 opening timing, the energization end timing, and the on-off valve 120 closing There is also a time lag between the start time. That is, an injection amount error between the actual fuel injection amount actually injected and the desired target fuel injection amount occurs due to the period and the timing difference. The ECU 112 cannot obtain a desired fuel injection amount at a desired time unless fuel injection is performed in consideration of these periods and time lags. The opening period and timing of the valve are determined by the fuel injection amount and the fuel pressure in the common rail 115. The ECU 112 has a map that determines the opening period and timing in consideration of the valve transition period from the fuel injection amount and the fuel pressure value, and transmits a fuel injection signal corresponding to the opening period and timing calculated from this map to the EDU 119. Ensure proper fuel injection.

  The fuel pressure in the direct injection fuel injection device that directly injects fuel into the combustion chamber 141 of the internal combustion engine is higher than the fuel pressure of the port injection fuel injection device that injects fuel into the intake port of the internal combustion engine. Therefore, when both inject the same amount of fuel, the opening period of the direct injection type fuel injection device is shorter than the opening period of the port injection type fuel injection device. When the opening period is shortened, the ratio of the valve transition period to the opening period is increased. That is, in the direct injection type fuel injection device, the influence of the period and the timing shift is larger than that of the port injection type fuel injection device.

  On the other hand, an air-fuel ratio error may occur between the target air-fuel ratio and the actually measured air-fuel ratio due to changes in operating conditions. At this time, the ECU calculates an A / F feedback value from the air-fuel ratio error, corrects the fuel injection amount so that the measured air-fuel ratio becomes the target air-fuel ratio by eliminating the air-fuel ratio error. The A / F feedback value is a correction value of the fuel injection amount calculated by the ECU in correlation with the difference between the actually measured air-fuel ratio and the target air-fuel ratio at a constant time interval.

  However, even if correction using the A / F feedback value is performed, there is a possibility that accurate fuel pressure and air flow rate may not be obtained due to individual differences or deterioration with time of the fuel pressure sensor 117 and the air flow meter 134. Even if an accurate value is obtained, a desired fuel injection amount may not be obtained due to individual differences or deterioration of the fuel injection device. In order to prevent this, the ECU 112 corrects the map according to the air-fuel ratio. This correction is performed using the learning value, and the learning value is obtained by learning value calculation processing. That is, the learning value is a correction value for correcting a difference between the target fuel injection amount and the actually measured fuel injection amount due to individual differences of the fuel injection devices 111 or the like or the occurrence of deterioration with time.

The fuel injection amount Q is determined by the following equation using the A / F feedback value faf and the learned value faf_learn.
Q = q × k × (1 + faf + faf_learn)
Here, q is an intake air amount, and k is a coefficient for calculating the fuel injection amount from the intake air amount.

  The A / F feedback value faf is 0 when the target air-fuel ratio matches the actually measured air-fuel ratio, and the learning value faf_learn is 0 when there is no individual difference or deterioration with time of the fuel injection device or the like. At this time, the fuel injection amount Q is obtained by multiplying the intake air amount q by a coefficient k.

  On the other hand, when an air-fuel ratio error occurs, the A / F feedback value faf is added to 1, and the fuel injection amount Q is obtained by multiplying the intake air amount q by coefficients k and 1 + faf. Thereby, the fuel injection amount is corrected so that the actually measured air-fuel ratio becomes the target air-fuel ratio. In addition to this, when individual differences or deterioration with time of the fuel injection device or the like occurs, the learning value faf_learn is added to the A / F feedback value faf, and the fuel injection amount Q multiplies the intake air amount q by a coefficient k and 1 + faf + faf_learn. Is required. Thereby, the difference between the target fuel injection amount and the actually measured fuel injection amount due to the individual difference of the fuel injection device or the like or the occurrence of deterioration with time is corrected.

  A learning value calculation process for calculating a learning value will be described with reference to FIG.

  The learned value calculation process is executed by the ECU at regular time intervals when the ECU operates. The initial value of the learning value faf_learn is set to 0. In step S21, it is determined whether the engine control is in the learning operation region. The determination depends on whether the engine speed and load and the engine coolant temperature are within a certain range. When it is not in the learning driving region, the process ends. When it is in the learning driving region, the process proceeds to step S22.

  In step S22, an average value fafav of the A / F feedback value is obtained. The average value fafav is obtained by taking an arithmetic average of A / F feedback values obtained during a certain period. For example, when there is no individual difference or deterioration with time of the fuel injection device and the sensor, the average value fafav becomes zero. On the other hand, when individual differences or deterioration with time of the fuel injection device and the sensor occurs, the average value fafav takes a non-zero value.

  In the next step S23, it is determined whether or not the average value fafav is equal to or less than the allowable value A. The allowable value A is a value determined in advance and stored in the ECU 112. When the average value fafav is less than or equal to the allowable value A, this process ends without updating the learning value. By determining whether or not to update the learning value using the allowable value A, it is possible to previously determine the individual difference or the degree of deterioration with time of the fuel injection device or the like that should update the learning value. In addition, if the learning value is updated when the average value fafav is small, the learning value may fluctuate frequently and the control may become unstable. This can be prevented.

  In step S24, a guard process for preventing the fluctuation range of the learning value from increasing is performed. The correction of the fuel injection amount is performed by adding the learning value to the A / F feedback value. For example, a value obtained by integrating the average value fafav is used as the learning value. In order to suppress the fluctuation range of the learning value in the guard process, when the average value fafav is larger than the predetermined value t, the learning value is updated with the average value fafav as t, and when the average value fafav is smaller than the predetermined value -t. Then, the learning value is updated by setting the average value fafav to -t. Control can be stabilized by suppressing the fluctuation range of the learning value to t.

  Next, in step S25, the learning value faf_learn is updated. The update is obtained by adding the average value fafav to the current learning value faf_learn. As a result, a learning value fal_learn is calculated, and the ECU corrects the map using the learning value.

  The A / F feedback value is calculated when there is a difference between the actually measured air-fuel ratio and the target air-fuel ratio, and the learning value is obtained by adding the average value of the A / F feedback values. The increase indicates that the injection amount error between the actual fuel injection amount actually injected in the fuel injection device 111 and the desired target fuel injection amount has increased. When multi-injection is performed while the learning value is increasing, an injection amount error is accumulated every time fuel injection is performed due to a period and a time lag, and the error between the actually measured air-fuel ratio and the target air-fuel ratio increases. In order to prevent this, an error between the actually measured air-fuel ratio and the target air-fuel ratio is minimized by performing the injection number reduction process described below to minimize the period and timing deviation.

  Next, the injection frequency reduction process according to the present embodiment will be described with reference to FIG.

  The injection frequency reduction process is repeatedly executed by the ECU at a certain time interval after the ignition switch of the vehicle is turned on.

  First, in step S31, it is determined whether the learning value is equal to or less than a specified value B. When it is equal to or less than the prescribed value B, the engine can be controlled using the learning value, and thus this process ends. When the learning value is larger than the specified value B, the process proceeds to the next step S32.

  In step S32, it is determined whether the fuel injection device is performing multi-injection. When the multi-injection is not performed, this process ends. If multi-injection is being performed, the process proceeds to step S33.

  In step S33, multi-injection is stopped and the number of injections is set to one. At this time, the total amount of fuel injected by all the injections is injected at a time. In the multi-injection, the error of the fuel injection amount increases as the learning value increases. However, according to the injection number reduction process, the fuel injection amount required by the engine 110 is ensured and the period and timing deviation in the fuel injection are minimized. Thus, the error between the actual air-fuel ratio and the desired air-fuel ratio can be minimized.

  Moreover, you may reduce the frequency | count of injection in step S33. At this time, the fuel is injected by the number of times obtained by reducing the total amount of fuel injected by all the injection times. As a result, even when the learning value increases, the fuel injection amount required by the engine 110 is ensured, while the period and timing deviation in the fuel injection are suppressed, and the error between the actual air-fuel ratio and the desired air-fuel ratio is minimized. It becomes possible to suppress.

  In the above-described embodiment, the multi-injection injects the fuel a plurality of times in the intake stroke. However, the present invention is not limited to this, and the fuel is injected a plurality of times in another stroke of the engine 110 or over a plurality of strokes. You may inject. That is, for example, fuel may be injected a plurality of times in the compression stroke, the expansion stroke, and the exhaust stroke after being injected in the intake stroke.

It is the figure which showed typically the fuel-injection system connected to the spark ignition type direct injection internal combustion engine. It is the flowchart which showed the learning value calculation process in a fuel-injection system. It is the flowchart which showed the injection frequency reduction process in a fuel-injection system.

Explanation of symbols

110 Engine 111 Fuel injection device 112 ECU
113 A / F sensor 114 Fuel pump 115 Common rail 117 Fuel pressure gauge 118 Injection port 119 EDU (Injector drive unit)
120 On-off valve 134 Air flow meter

Claims (3)

An air-fuel ratio measuring means attached to the exhaust system of the internal combustion engine;
Fuel injection means for injecting fuel directly into the combustion chamber of the internal combustion engine and divided into a predetermined number of times per combustion;
Learning value calculation means for calculating a learning value used to correct the fuel injection amount so as to reduce the air-fuel ratio error between the target air-fuel ratio and the actual air-fuel ratio measured by the air-fuel ratio measurement means;
The fuel injection system, wherein the fuel injection means decreases the predetermined number of times when the learning value deviates from a normal range.   The fuel injection system according to claim 1, wherein the fuel injection unit sets the predetermined number of times to 1 when the learning value exceeds a specified value. A spark ignition direct injection internal combustion engine comprising the fuel injection system according to claim 1.

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