Method and device for controlling injection timing of a direct-injection spark-ignition internal combustion engine

Abstract

To make the suppression of the number of exhaust particulates and the best fuel consumption operation compatible.SOLUTION: An injection timing control device of a cylinder direct injection spark ignition internal combustion engine is equipped with a cooling-down injection timing map that assigns a basic injection timing that minimizes the number of exhaust particulates at the time of cooling-down, and a warming-up injection timing map that assigns a basic injection timing that minimizes the number of exhaust particulates at the time of warming-up. At the time of cooling-down, the basic injection timing read out from the cooling-down injection timing map is corrected to an advance side so as to approach a knocking best injection timing to be a target injection timing within a range in which the number of exhaust particulates detected by a PN sensor does not exceed a predetermined permissible level. At the time of warming-up, the basic injection timing read out from the warming-up injection timing map is corrected to a delay side so as to approach the knocking best injection timing to be a target injection timing within a range in which the number of exhaust particulates does not exceed the predetermined permissible level.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to injection timing control for a direct injection spark ignition internal combustion engine, taking into consideration exhaust particulate number (PN) and knocking. [Background technology]

[0002] In direct-injection spark-ignition internal combustion engines, the number of exhaust particulates is generally a greater problem than in port-injection spark-ignition internal combustion engines. The number of exhaust particulates emitted by vehicle internal combustion engines is regulated by law in many countries. Meanwhile, with the recent trend toward higher compression ratios, even direct-injection spark-ignition internal combustion engines are prone to knocking. When knocking occurs, ignition timing is retarded as a knock suppression control, resulting in less than optimal fuel economy.

[0003] In a direct-injection spark-ignition internal combustion engine, the amount of exhaust particulates and the occurrence of knocking are affected by the injection timing. Therefore, in many practical engines, the injection timing that provides an appropriate compromise between the number of exhaust particulates and knocking is pre-assigned to a map using engine speed and load as parameters, and the injection timing is controlled using this map. In this invention, "injection timing" refers to the injection start timing, and in the case of multiple injections, it refers to the injection start timing of the first injection.

[0004] Patent Document 1 discloses that in a direct-injection spark-ignition internal combustion engine, when the fuel is heavy fuel, the injection timing is advanced to ensure a long atomization time until the ignition timing, thereby improving drivability and exhaust emissions. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-232575 Summary of the Invention [Problem to be solved by the invention]

[0006] The above-mentioned conventional technology simply advances the injection timing depending on the degree of heaviness of the fuel, and does not control the injection timing taking into account the occurrence of knocking (in other words, retarding the ignition timing) or the relationship with the engine temperature. [Means for solving the problem]

[0007] The present invention provides an injection timing control method for a direct injection spark ignition internal combustion engine, comprising: a cold-engine injection timing map allocating basic injection timings corresponding to engine speeds and loads so that the number of exhaust particulates is minimized under conditions where the temperature of the internal combustion engine is relatively low, and a warm-engine injection timing map allocating basic injection timings corresponding to engine speeds and loads so that the number of exhaust particulates is minimized under conditions where the temperature of the internal combustion engine is relatively high, The number of exhaust particles emitted from an internal combustion engine is directly detected or estimated from the fuel properties, Under conditions where the temperature of the internal combustion engine is relatively low, the basic injection timing read from the cold-engine injection timing map is corrected to the advance side so as to approach the best injection timing for preventing knocking, which minimizes the amount of ignition timing retard due to knocking of the internal combustion engine, within a range in which the number of exhaust particulates does not exceed a predetermined allowable level, and the target injection timing is set as the corrected injection timing; Under conditions where the temperature of the internal combustion engine is relatively high, the basic injection timing read from the warm-up injection timing map is corrected to the retard side so as to approach the best injection timing for knocking, which minimizes the amount of ignition timing retard due to knocking of the internal combustion engine, within a range in which the number of exhaust particulates does not exceed a predetermined allowable level, and is set as the target injection timing.

[0008] That is, when the temperature of the internal combustion engine is relatively low, i.e., when the engine is cold, the injection timing that minimizes the number of exhaust particulates (i.e., the basic injection timing) is retarded from the best knocking injection timing. Therefore, by correcting the basic injection timing to the advance side so that it approaches the best knocking injection timing within a range in which the number of exhaust particulates does not exceed an allowable level, it is possible to obtain an injection timing that is as close as possible to the best knocking injection timing while keeping the number of exhaust particulates within an allowable level. In this case, the target injection timing is obtained on the retard side from the best knocking injection timing.

[0009] On the other hand, when the temperature of the internal combustion engine is relatively high, i.e., when the engine is warmed up, the injection timing that minimizes the number of exhaust particulates (in other words, the basic injection timing) is more advanced than the best injection timing against knocking. Therefore, by correcting the basic injection timing to the retard side so that it approaches the best injection timing against knocking within a range in which the number of exhaust particulates does not exceed an allowable level, it is possible to obtain an injection timing that is as close as possible to the best injection timing against knocking while keeping the number of exhaust particulates within an allowable level. In this case, the target injection timing is obtained more advanced than the best injection timing against knocking. [Effects of the Invention]

[0010] According to this invention, the number of exhaust particulates can be kept within an acceptable level both when the internal combustion engine is cold and when it is warmed up, while the injection timing can be set as close as possible to the best injection timing for preventing knocking, thereby achieving both suppression of the number of exhaust particulates and improvement of fuel efficiency. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is an explanatory diagram showing the configuration of an internal combustion engine according to an embodiment; [Figure 2] A characteristic diagram showing the characteristics of (a) compression end temperature, (b) fuel uniformity, and (c) MB50 with respect to the injection timing during warm-up. [Figure 3] This is a characteristic diagram showing the PN characteristics with respect to the injection timing during warm-up. [Figure 4] A characteristic diagram showing the characteristics of (a) wall-attached PN and (b) tip soot PN with respect to the injection timing. [Figure 5] A characteristic diagram showing the change in the ratio of wall-attached PN and tip soot PN with respect to wall temperature. [Figure 6] A characteristic diagram showing the characteristics of (a) compression end temperature, (b) fuel uniformity, and (c) MB50 with respect to injection timing during cold engine operation. [Figure 7] This is a characteristic diagram showing the PN characteristics with respect to the injection timing when the engine is cold. [Figure 8] A characteristic diagram showing the relationship between fuel properties during warm-up and the allowable PN level. [Figure 9] A characteristic diagram showing the relationship between fuel properties when cold and the allowable PN level. DETAILED DESCRIPTION OF THE INVENTION

[0012] An embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

[0013] 1 shows the system configuration of a direct-cylinder injection spark-ignition internal combustion engine 1 according to one embodiment. This internal combustion engine 1 is a four-stroke spark-ignition internal combustion engine having a pair of intake valves 4 and a pair of exhaust valves 5 arranged on the ceiling wall of a combustion chamber 3, with an ignition plug 6 arranged in the center surrounded by these intake valves 4 and exhaust valve 5. Also arranged adjacent to the spark plug 6 is a fuel injection valve 7 that injects fuel directly into the combustion chamber 3. This fuel injection valve 7 is an electromagnetic or piezoelectric injection valve that opens when a drive pulse signal is applied, and injects an amount of fuel that is substantially proportional to the pulse width of the drive pulse signal.

[0014] An electronically controlled throttle valve 13, the opening of which is controlled by a control signal from the engine controller 8, is installed upstream of the collector section 12 in the intake passage 11 connected to the intake port 10. An air flow meter 14, which detects the amount of intake air, is disposed upstream of the throttle valve 13, and an air cleaner 15 is disposed further upstream.

[0015] A catalytic device 18 consisting of a three-way catalyst is installed in an exhaust passage 17 connected to the exhaust port 16, and an air-fuel ratio sensor 19 for detecting the air-fuel ratio and a PN sensor 20 for detecting the number of exhaust particulates contained in the exhaust are disposed upstream of the catalytic device 18. Various types and styles of PN sensors 20 are available, but any type and style may be used in the present invention.

[0016] The internal combustion engine 1 is also provided with a water temperature sensor 21 at an appropriate position that detects the coolant temperature as a temperature parameter that represents the engine temperature. Note that other parameters, such as lubricating oil temperature, may also be used as the temperature parameter that represents the engine temperature. Furthermore, a knocking sensor 22 for detecting knocking is provided at an appropriate position, such as in the cylinder block of the internal combustion engine 1. Note that knocking may also be detected using an in-cylinder pressure sensor.

[0017] The engine controller 8 receives detection signals from the air flow meter 14, air-fuel ratio sensor 19, PN sensor 20, water temperature sensor 21, and knocking sensor 22, as well as detection signals from a number of other sensors, such as a crank angle sensor 25 for detecting engine speed and an accelerator pedal position sensor 26. Based on these input signals, the engine controller 8 optimally controls the amount and timing of fuel injection by the fuel injection valve 7, the ignition timing by the spark plug 6, the opening of the throttle valve 13, and the like.

[0018] For example, with regard to the ignition timing, the engine controller 8 performs known ignition timing retard control based on the knocking detection by the knocking sensor 22. In other words, if no knocking is occurring, the ignition timing is gradually advanced so as to approach the MBT point as much as possible, and if knocking is detected, the ignition timing is retarded, for example, by a certain amount. As a result, the ignition timing is controlled so as to maintain a weak knocking state. From the standpoint of fuel economy, the best fuel economy is generally achieved when the ignition timing is near the MBT point.

[0019] Next, the injection timing control, which is a main part of the present invention, will be described. The engine controller 8 is provided with a cold-engine injection timing map that allocates basic injection timings corresponding to the engine speed and load so as to minimize the number of exhaust particulates when the temperature of the internal combustion engine 1 is relatively low, and a warm-up injection timing map that allocates basic injection timings corresponding to the engine speed and load so as to minimize the number of exhaust particulates when the temperature of the internal combustion engine 1 is relatively high.

[0020] Then, under conditions where the temperature of the internal combustion engine 1 is relatively low (i.e., when the engine is cold), the basic injection timing read from the cold injection timing map is corrected to the advance side so as to approach the best injection timing for knocking, which minimizes the amount of ignition timing retard due to knocking of the internal combustion engine 1, within a range in which the number of exhaust particulates detected by the PN sensor 20 does not exceed a predetermined allowable level, and this is set as the target injection timing.

[0021] In addition, under conditions where the temperature of the internal combustion engine is relatively high (i.e., when the engine is warmed up), the basic injection timing read from the warm-up injection timing map is corrected to the retard side so as to approach the best injection timing for knocking, which minimizes the amount of ignition timing retard due to knocking of the internal combustion engine 1, within a range in which the number of exhaust particulates detected by the PN sensor 20 does not exceed a predetermined allowable level, and is used as the target injection timing.

[0022] The cold start and warm up periods can be distinguished, for example, by an appropriate threshold temperature. For example, the coolant temperature after warm up is about 70 to 90°C, and the coolant temperature at cold start is about 30°C or less, so an appropriate threshold temperature can be set between these values.

[0023] Figure 2 is a characteristic diagram showing the characteristics of (a) compression end temperature, (b) fuel uniformity, and (c) MB50, which are related to knocking, with the horizontal axis representing the injection timing, and particularly shows the characteristics during warm-up. Note that the characteristics shown in Figures 2 to 10 are all somewhat simplified for the purpose of explanation, and are shown at a certain operating point (rotation speed and load). Furthermore, although no specific numerical values ​​are given for the injection timing on the horizontal axis in each diagram, it corresponds to a section of approximately 360° CA spanning from the intake stroke (piston downstroke) after intake top dead center to the compression stroke (piston upstroke).

[0024] (a) The compression end temperature is the combustion chamber gas temperature at the ignition timing, but due to the influence of the heat of vaporization of the fuel spray, the later the injection timing, as shown in the figure, the lower it becomes, which is advantageous in terms of knocking. (b) Fuel uniformity indicates the uniformity of the fuel components within the combustion chamber 3, but in order to ensure time until the ignition timing, the earlier the injection timing, as shown in the figure, the better it becomes, which is advantageous in terms of knocking.

[0025] Therefore, due to these two characteristics, knocking is less likely to occur at crank angles near the middle (roughly corresponding to the intake valve closing timing), but is more likely to occur at crank angles both further advanced and further retarded.

[0026] (c) MB50 indicates the so-called combustion center of gravity, which takes into account the ignition timing retard associated with knocking. As shown in the figure, the ignition timing is near the MBT point at an intermediate crank angle where knocking is unlikely to occur, resulting in MB50 being advanced. Therefore, this intermediate crank angle (shown as "Knock best") is the best injection timing for preventing knocking, as it minimizes the amount of ignition timing retard associated with knocking. This is also the injection timing that provides the best fuel economy.

[0027] On the other hand, Figure 3 is a characteristic diagram showing the PN (exhaust particulate count) characteristics with respect to the injection timing during warm-up. As shown in the figure, during warm-up, the number of exhaust particulates is minimum when the injection timing is at a relatively advanced crank angle (shown as "PN best"), which corresponds to the first half of the intake stroke. The number of exhaust particulates increases at both the advanced and retarded crank angles. As an example, the number of exhaust particulates is minimum at around 60 to 80 degrees ATDC.

[0028] Exhaust particulates can be broadly divided into those generated when liquid fuel adhering to the combustion chamber wall is exposed to flame, and those generated when liquid fuel adhering to the tip of the fuel injector 7 is exposed to flame. Here, the number of exhaust particulates resulting from the former is referred to as wall-adhered PN, and the number of exhaust particulates resulting from the latter is referred to as tip soot PN. Figures 4(a) and (b) show the characteristics of these with respect to the injection timing. Wall-adhered PN exhibits a W-shaped characteristic as shown in Figure 4(a), depending on the piston crown position, spray penetration, and other factors. Note that Figure 4(a) shows the characteristics at a relatively low temperature. Tip soot PN increases as the injection timing is delayed, because the later the injection timing, the shorter the time until ignition timing (the time it takes for the fuel adhering to the tip to vaporize).

[0029] Furthermore, as shown in FIG. 5, the lower the wall temperature of the combustion chamber (that is, the temperature of the internal combustion engine 1), the larger the wall adhesion PN becomes, while the tip soot PN does not decrease even when the temperature rises and remains roughly constant.

[0030] Therefore, the influence of wall-attached PN is relatively small during warm-up, resulting in the characteristics shown in Figure 3.

[0031] In the warm-up injection timing map described above, which uses the engine speed and load as parameters, the injection timing at which the number of exhaust particulates is minimized, shown as "PN best" in Figure 3, is assigned as the basic injection timing for each operating point.

[0032] The actual target injection timing is obtained by correcting the basic injection timing read from the warm-up injection timing map to the retard side so as to approach the best injection timing against knocking (crank angle shown as "Knock best") within a range in which the number of exhaust particulates detected by the PN sensor 20 does not exceed a predetermined allowable level. In other words, as is clear from Figures 3 and 2(c), the injection timing that minimizes the number of exhaust particulates is on the advance side of the best injection timing against knocking, so by retarding the injection timing until the number of exhaust particulates reaches an allowable level, it is possible to obtain the injection timing that is closest to the best injection timing against knocking while keeping the number of exhaust particulates within an allowable level.

[0033] For example, by repeating control such as retarding the injection timing by a fixed small amount each cycle and then advancing the injection timing by a fixed amount when the number of exhaust particulates exceeds an acceptable level, it is possible to maintain the number of exhaust particulates near an acceptable level while maintaining the most retarded crank angle position (the crank angle position closest to the best injection timing for preventing knocking).

[0034] Next, Figure 6, like Figure 2, is a characteristic diagram showing the characteristics of (a) compression end temperature, (b) fuel uniformity, and (c) MB50, which are involved in knocking, with the horizontal axis representing the injection timing, and particularly shows the characteristics when the engine is cold.The basic tendency when the engine is cold is the same as when the engine is warm (Figure 2), and the intermediate crank angle (near the intake valve closing timing) is the best injection timing for knocking ("Knock best"), as it minimizes the amount of ignition timing retard associated with knocking.

[0035] Figure 7 is a characteristic diagram showing the PN characteristics with respect to the injection timing when the engine is cold. As shown in Figure 5, when the engine is cold, the wall-adhering PN is large, and as a result, the injection timing (PN best) that minimizes the number of exhaust particulates occurs near a crank angle slightly delayed from the intake bottom dead center, as shown in Figure 7.

[0036] In the cold-engine injection timing map described above, which uses the engine speed and load as parameters, the injection timing at which the number of exhaust particulates is minimized, shown as "PN best" in Figure 7, is assigned as the basic injection timing for each operating point.

[0037] The actual target injection timing is obtained by correcting the basic injection timing read from the cold engine injection timing map to the advance side so as to approach the best injection timing against knocking (crank angle shown as "Knock best") within a range in which the number of exhaust particulates detected by the PN sensor 20 does not exceed a predetermined allowable level. In other words, as is clear from Figures 7 and 6(c), the injection timing at which the number of exhaust particulates is minimum is on the retard side of the best injection timing against knocking. Therefore, by advancing the injection timing until the number of exhaust particulates reaches an allowable level, it is possible to obtain the injection timing that is closest to the best injection timing against knocking while keeping the number of exhaust particulates within an allowable level.

[0038] For example, by repeating control such as advancing the injection timing by a fixed small amount each cycle and then retarding the injection timing by a fixed amount when the number of exhaust particulates exceeds an acceptable level, it is possible to maintain the number of exhaust particulates near an acceptable level while maintaining the most advanced crank angle position (the crank angle position closest to the best injection timing for preventing knocking).

[0039] In this way, in the above embodiment, appropriate injection timing control can be performed both when the engine is warmed up and when it is cold, thereby achieving both suppression of the number of exhaust particulates and improvement of fuel economy. Furthermore, although the number of exhaust particulates is affected by, for example, the fuel properties (heavy or light), even if the number of exhaust particulates varies depending on the fuel properties, by controlling the number of exhaust particulates detected by the PN sensor 20 to be within an allowable level, the number of exhaust particulates does not increase.

[0040] Although the above describes an embodiment in which the PN sensor 20 is provided in the exhaust system to monitor the actual number of exhaust particulates, this invention can be similarly implemented by estimating the number of exhaust particulates according to the fuel properties (heaviness) without using the PN sensor 20. The fuel properties (heaviness) can be detected by any known appropriate method.

[0041] The heavier the fuel, the greater the number of exhaust particulates. Therefore, by using the PN index, which indicates the amount of exhaust particulates instead of the degree of heaviness, it is possible to determine whether the number of exhaust particulates for the injection timing is within the allowable level, as shown in Figures 8 and 9.

[0042] 8 shows the relationship between the heaviness of the fuel during warm-up and the permissible level LimH for the number of exhaust particulates. In this case, the number of exhaust particulates falls within the permissible level if the fuel is more advanced than the permissible level LimH. The heavier the fuel, the more advanced the permissible level LimH. In other words, during warm-up, the permissible level LimH is the retard limit. If the fuel is light, the injection timing can be retarded to approach the optimal injection timing for preventing knocking, but if the fuel is heavy, the injection timing is limited to the more advanced side.

[0043] Figure 9 shows the relationship between the degree of fuel heaviness during cold engine operation and the permissible level LimC for the number of exhaust particulates. In this case, the number of exhaust particulates falls within the permissible level if the injection timing is more retarded than the permissible level LimC. The heavier the fuel, the more retarded the permissible level LimC becomes. In other words, during cold engine operation, the permissible level LimC is the advance limit. If the fuel is light, the injection timing can be advanced to approach the optimal injection timing for preventing knocking. However, the heavier the fuel, the more the injection timing is restricted to a more retarded side. [Explanation of symbols]

[0044] 1...Internal combustion engine 6...Spark plug 7...Fuel injection valve 8...Engine controller 20...PN sensor 21...Water temperature sensor 22...Knocking sensor

Claims

1. 1. A method for controlling injection timing of a direct injection spark ignition internal combustion engine, comprising: a cold-engine injection timing map allocating basic injection timings corresponding to engine speeds and loads so that the number of exhaust particulates is minimized under conditions where the temperature of the internal combustion engine is relatively low, and a warm-engine injection timing map allocating basic injection timings corresponding to engine speeds and loads so that the number of exhaust particulates is minimized under conditions where the temperature of the internal combustion engine is relatively high, The number of exhaust particles emitted from an internal combustion engine is directly detected or estimated from the fuel properties, Under conditions where the temperature of the internal combustion engine is relatively low, the basic injection timing read from the cold-engine injection timing map is corrected to the advance side so as to approach the best injection timing for preventing knocking, which minimizes the amount of ignition timing retard due to knocking of the internal combustion engine, within a range in which the number of exhaust particulates does not exceed a predetermined allowable level, and the target injection timing is set as the corrected injection timing; Under conditions where the temperature of the internal combustion engine is relatively high, the basic injection timing read from the warm-up injection timing map is corrected to the retard side so as to approach the best injection timing for preventing knocking, which minimizes the amount of ignition timing retard caused by knocking of the internal combustion engine, within a range in which the number of exhaust particulates does not exceed a predetermined allowable level, and the target injection timing is set. A method for controlling injection timing in a direct-injection spark-ignition internal combustion engine.

2. The number of exhaust particulates is detected using a PN sensor provided in the exhaust system of the internal combustion engine.

2. The method for controlling injection timing for a direct injection spark ignition internal combustion engine according to claim 1.

3. As the fuel properties, the degree of heaviness of the fuel used is detected, and the number of exhaust particulates corresponding to the injection timing is estimated from predetermined characteristics, assuming that the heavier the fuel, the greater the number of exhaust particulates.

2. The method for controlling injection timing for a direct injection spark ignition internal combustion engine according to claim 1.

4. The injection timing varies within the intake and compression strokes.

2. The method for controlling injection timing for a direct injection spark ignition internal combustion engine according to claim 1.

5. The basic injection timing in the cold injection timing map is after the intake bottom dead center, and the basic injection timing in the warm injection timing map is before the intake bottom dead center.

2. The method for controlling injection timing for a direct injection spark ignition internal combustion engine according to claim 1.

6. a direct-injection spark-ignition internal combustion engine; a sensor for detecting knocking; a sensor for directly or indirectly detecting the number of exhaust particles emitted from an internal combustion engine; a sensor for detecting the temperature of the internal combustion engine; A controller; Equipped with The above controller is Ignition timing control is performed based on knocking detection, a cold-engine injection timing map allocating basic injection timings corresponding to engine speeds and loads so that exhaust particulates are minimized under conditions where the temperature of the internal combustion engine is relatively low, and a warm-engine injection timing map allocating basic injection timings corresponding to engine speeds and loads so that exhaust particulates are minimized under conditions where the temperature of the internal combustion engine is relatively high, Under conditions where the temperature of the internal combustion engine is relatively low, the basic injection timing read from the cold-engine injection timing map is corrected to the advance side so as to approach the best injection timing for preventing knocking, which minimizes the amount of ignition timing retard due to knocking of the internal combustion engine, within a range in which the number of exhaust particulates does not exceed a predetermined allowable level, and the target injection timing is set as the corrected injection timing; Under conditions where the temperature of the internal combustion engine is relatively high, the basic injection timing read from the warm-up injection timing map is corrected to the retard side so as to approach the best injection timing for preventing knocking, which minimizes the amount of ignition timing retard caused by knocking of the internal combustion engine, within a range in which the number of exhaust particulates does not exceed a predetermined allowable level, and the target injection timing is set. An injection timing control device for a direct-injection spark-ignition internal combustion engine.

Images