JP5522020B2 - Fuel injection control device for on-board diesel engine - Google Patents

Description

 The present invention relates to a fuel injection control device for a diesel engine mounted on a vehicle.

 In a diesel engine to which fuel mainly composed of light oil is supplied, pre-fuel injection for premixed combustion may be performed before main fuel injection for diffusion combustion. Patent Document 1 discloses one in which pre-fuel injection is performed a plurality of times.

JP 2009-293383 A

By the way, in a diesel engine, vibration generated by combustion is considerably large. Therefore, when a diesel engine is mounted on a vehicle such as an automobile, the vibration generated by the engine gives an uncomfortable feeling to the occupant, and vibration in the frequency range of 200 to 800 HZ is not obtained particularly in a high load low speed range. It gives a pleasant feeling. For this reason, uncomfortable engine vibrations are hardly transmitted to the vehicle body by devising the structure of the engine mount interposed between the engine and the vehicle body.

As one of the causes of vibration generation of a diesel engine, there is vibration due to a large peak value of the heat generation rate (that is, combustion pressure). That is, in recent diesel engines, by performing high pressure fuel injection and supercharging, the heat generation rate (the amount of heat generated per unit crank angle, also referred to as the heat generation rate) tends to be extremely large. The larger the peak value of the heat generation rate, the larger the peak value of the combustion pressure, and the greater the vibration. The technique disclosed in Patent Document 1 aims at optimizing the fuel injection timing in consideration of the delay limit of main fuel injection and the advance limit of pre-fuel injection, and is an injection for reducing engine vibration. Timing setting is not taken into consideration. Note that reducing the fuel injection amount in order to reduce the peak value of the heat generation rate is not preferable because of a reduction in torque.

 The present invention has been made in consideration of the above-described circumstances, and its purpose is to mount a vehicle that can reduce the engine vibration itself by reducing the peak value of the heat generation rate while securing the torque. It is to provide a fuel injection control device for a diesel engine.

In order to achieve the above object, the following solution is adopted in the present invention. That is, as described in claim 1 in the claims,
In a fuel injection control device for a vehicle-mounted diesel engine that is mounted on a vehicle and supplied with fuel mainly composed of light oil,
In at least the low speed region of the engine high load region, the main fuel injection for diffusion combustion is divided injection that is performed in a plurality of times,
The injection amount of the second stage split injection is greater than the injection quantity of the first stage split injection ,
The geometric compression ratio of the engine is 15 or less,
Pre-fuel injection for premixed combustion is performed before the main fuel injection in at least a low speed region of the engine high load region,
The divided injection is made 3 times or more,
The injection amount of the last stage in the divided injection is made smaller than the injection quantity of the divided injection of the immediately preceding stage,
The injection amount in each of the three or more divided injections is changed so that the injection amount is initially increased, and thereafter, the injection amount is changed so as to be reduced.
When the injection amount is changed so as to be increased by the divided injection, the injection amount in the divided injection executed before is 50 to 75% of the injection amount in the immediately following divided injection,
When it is changed so that the injection amount is reduced by the divided injection, the injection amount in the divided injection executed later is 85 to 90% of the injection amount in the immediately preceding divided injection.
It is like that.

 According to the above solution, the peak value of the heat generation rate is reduced by dividing the main fuel injection at least in the low speed region of the high load region of the engine where the engine mount vibration becomes sensitive, and vibration is generated. Can be reduced. In particular, by increasing the injection amount of the second-stage split injection more than the injection amount of the first-stage split injection, the heat generation rate of the entire diffusion combustion is made to approximate a gentle mountain shape. This is extremely effective in reducing vibrations, and is sufficient for preventing the increase in smoke because a sufficient amount of oxygen is required when the fuel is burned by the split injection in the second stage. Of course, since the fuel injection amount as a whole of the main fuel injection can be sufficiently secured by the divided injection, the torque can be sufficiently secured. Further, as compared with the case where the main fuel injection is only one stage, it is only about the same fuel consumption to secure the same torque, and there is no problem in terms of fuel consumption.

In addition to the above, it is preferable to shorten the ignition delay due to the low compression ratio by the pre-fuel injection, to reduce the delay of the diffusion combustion start, and to ensure a sufficient period of divided injection. Moreover, it becomes more preferable in terms of vibration reduction as a form in which the heat generation ratio of the entire diffusion combustion is approximated by a gentle mountain shape.

Supercharging is performed at least in the low speed region of the engine high load region (corresponding to claim 2 ). In this case, the torque reduction due to the low compression ratio can be eliminated by supercharging, and sufficient torque can be secured.

The interval between the first-stage divided injection and the second-stage divided injection is made shorter than the interval between the pre-fuel injection and the first-stage divided injection (corresponding to claim 3 ). . In this case, the interval between the first-stage divided injection and the second-stage divided injection is shortened, which is preferable in terms of securing the torque.

Supercharging is performed at least in the low speed range of the engine high load range,
In accordance with the increase in the intake charge amount due to the supercharging, the fuel injection amount is increased in a range where the excess air ratio λ is 1 or more.
(Corresponding to claim 4 ). In this case, it is preferable for securing the torque.

In the high speed range of the engine high load range, the main fuel injection is performed in one stage without being divided (corresponding to claim 5 ). In this case, in the high-load high-speed range of the engine in which the problem of vibration does not occur, diffusion combustion by main fuel injection is performed near the compression top dead center, which is preferable in terms of securing torque and improving fuel efficiency.

 According to the present invention, it is possible to reduce the vibration by reducing the peak value of the heat generation rate while securing the torque.

The simplified top view which shows the example of mounting to the vehicle of a diesel engine. The figure which shows the example of the intake-exhaust system of a diesel engine. The figure which shows the example of a setting of the injection quantity when main fuel injection is divided into 2 times. The figure which shows the example of a setting of the injection quantity when the main fuel injection is divided into 4 times. The figure which shows the heat generation rate at the time of the injection aspect in FIG. The figure which shows the heat generation rate when main fuel injection is divided into 3 times. The figure which shows the heat generation rate when the main fuel injection is divided into 4 times. The figure which shows the heat generation rate when main fuel injection is divided into 5 times. The figure which shows the mode of a vibration reduction when main fuel injection is made into 2-5 divided injection.

In FIG. 1, reference numeral 1 denotes an engine (engine body), which is an in-line four-cylinder automobile diesel engine in the embodiment. The engine 1 is attached to the vehicle body BD while being integrated with the transmission TR. In the embodiment, in a state where the engine 1 is placed horizontally in the front part of the vehicle body BD (in the engine room formed therein), the vehicle body BD (the front frame) is connected to the vehicle body BD via the three mount members 1M, 3M, and 4M. Installed.

As shown in FIG. 2, the engine 1 includes a cylinder 2, a cylinder head 3, and a piston 4 as is well known. An intake port 6 and an exhaust port 7 are opened with respect to the combustion chamber 5 formed above the piston 4. The intake port 6 is opened and closed by an intake valve 8, and the exhaust port 7 is opened and closed by an exhaust valve 9. A fuel injection valve 10 is attached to the cylinder head 3 so as to face the combustion chamber 5. In the embodiment, the fuel injection is of a common rail type, and extremely high pressure fuel is injected from the fuel injection valve 10. The geometric compression ratio of the engine 1 is a low compression ratio of 15 or less (14.2 in the embodiment). The geometric compression ratio can be set to a smaller compression ratio as long as ignitability and ignition delay are not a problem, but is preferably set to 12 or more for automobiles.

 In the intake passage 20 connected to the intake port 6, the air cleaner 21, the compressor wheel 22 a of the first exhaust turbocharger 22, and the compressor of the second exhaust turbocharger 23 are sequentially arranged from the upstream side to the downstream side. A wheel 23a, an intercooler 24, a throttle valve 25, and a surge tank 26 are provided. The surge tank 26 and each cylinder (the intake port 6 thereof) are independently connected by a branched intake passage 27.

 A bypass passage 28 is provided in the intake passage 20. The bypass passage 28 has an upstream end opened to the intake passage 20 between the compressor wheels 22a and 23a. Further, the downstream end of the bypass passage 28 is opened to the intake passage 20 between the compressor wheel 23 a and the intercooler 24. A control valve 29 is disposed in the bypass passage 28.

 In the exhaust passage 30 connected to the exhaust port 7, the turbine wheel 23 b of the second exhaust turbocharger 23, the turbine wheel 22 b of the first exhaust turbocharger 22, sequentially from the upstream side to the downstream side thereof, An oxidation catalyst 31 and a DPF 32 are connected.

 The exhaust passage 30 has a bypass passage 33 and a wastegate passage 34. The upstream end of the bypass passage 33 is opened to the exhaust passage 30 on the upstream side of the turbine wheel 23b. The downstream end of the bypass passage 33 is opened to the exhaust passage 30 between the turbine wheels 22b and 23b. A control valve 35 is disposed in the bypass passage 33.

The upstream end of the wastegate passage 34 is opened in the exhaust passage 30 between the turbine wheels 22b and 23b. The downstream end of the waste gate passage 34 is opened to the exhaust passage 30 between the turbine wheel 22 b and the oxidation catalyst 31. A wastegate valve 36 is disposed in the wastegate passage 34.

 The first exhaust turbo-type supercharger 22 is large, and the second exhaust turbo-type supercharger 23 is small. In the low rotation and low load range, supercharging is performed mainly by the small second exhaust turbocharger 23, and at this time, the control valves 29 and 35 are closed. In the high load range, supercharging is performed mainly by the large exhaust turbocharger 22, and at this time, the control valves 28 and 33 are opened. In the embodiment, the control valves 29 and 35 are controlled by the controller U configured using a microcomputer based on a map set with the engine speed and the engine load (for example, accelerator opening) as parameters. The When the supercharging pressure exceeds a predetermined upper limit pressure, the waste gate valve 36 is opened. It should be noted that the control valves 29 and 35 are intermediate in the transition period from the state of being mainly charged by the small exhaust turbocharger 23 to the state of being mainly charged by the large exhaust turbocharger 22. It may be an opening. In addition, since such supercharging control itself is not directly related to the present invention, further explanation is omitted.

 The intake passage 20 and the exhaust passage 30 are connected via an EGR passage 50. The upstream end of the EGR passage 50 is opened to the exhaust passage 30 upstream of the turbine wheel 23b. Further, the downstream end of the EGR passage 50 is opened to the intake passage 20 between the throttle valve 25 and the surge tank 26.

 An EGR cooler 51 is connected to the EGR passage 50, and an EGR valve 52 is disposed on the downstream side of the EGR cooler 51. The EGR passage 50 is provided with a bypass passage 53 that bypasses the EGR cooler 51. The bypass passage 53 has an upstream end opened to the EGR passage 50 upstream of the EGR cooler 51, and a downstream end opened to the EGR passage 50 downstream of the EGR valve 52. A control valve 54 is disposed in the bypass passage 54.

Here, fuel injection control from the fuel injection valve 10 is performed by a controller U (see FIG. 2) configured using a microcomputer. The controller U is input with signals from at least sensors for detecting the engine load (accelerator opening and supercharging pressure) and engine speed, and controls the root fuel injection valve 10. The fuel injection basically includes one pre-fuel injection for premixed combustion and one main fuel injection for diffusion combustion. The pre-fuel injection is performed before the compression top dead center (the pre-fuel injection is executed at the timing when the premixed combustion by the pre-fuel injection is finished before the compression top dead center). The injection timing of the main fuel injection is set so that diffusion combustion is performed from the vicinity of the compression top dead center to the expansion stroke after the compression top dead center.

In a high load / low speed range where engine vibration is set in advance (for example, stored in the controller U at a load of 70% or more of the total load and a rotation range of 2000 rpm or less), the main fuel The injection is divided injection that is performed by dividing the injection into a plurality of times. An example in which the main fuel injection is divided into two split injections is shown in FIG. 3, and an example in which four split injections are made is shown in FIG. 3 and 4, the horizontal axis indicates the crank angle, and the vertical axis indicates the fuel injection amount (the upper end position of each fuel injection indicates the fuel injection amount).

In the case of the reference example in which the main fuel injection is divided into two divided injections, as shown in FIG. 3, the injection amount of the first-stage divided injection is, for example, 50 to 75% of the injection amount of the second-stage divided injection. And so on. The peak value of the heat generation rate during diffusion combustion is reduced by the divided injection. In addition, by reducing the injection amount of the first-stage split injection, it is possible to suppress a rapid increase in the rate of heat generation at the beginning of diffusion combustion, and to increase the injection amount of the subsequent second-stage split injection. Thus, torque is secured. Further, by reducing the injection amount of the first-stage divided injection, a sufficient amount of oxygen is secured in the second-stage divided injection, which is preferable in terms of reducing or suppressing smoke.

In order to reduce engine vibration, it is preferable that the connecting line connecting the peak values of the heat generation ratio be approximated to a gentle mountain shape that gradually increases and then gradually decreases. In order to ensure such a configuration, when the divided injection is performed three times or more as in the present invention , for example, when divided injection is performed in four times as shown in FIG. 4, the final stage (in the case of FIG. 4) The injection amount of the divided injection at the fourth stage is preferably smaller than the injection amount of the divided injection at the immediately preceding stage (the third stage in the case of FIG. 4) (for example, the injection quantity of the immediately preceding divided injection) 85% to 90%).

5 to 8 show the heat generation rate when the number of divided injections is made different. First, FIG. 5 shows the case of two-stage split injection (corresponding to the injection mode of FIG. 3). The broken line in the figure indicates the heat generation rate in the conventional case where the main fuel injection is performed only once, and the alternate long and short dash line indicates an ideal state in which the heat generation rate changes gradually in a mountain-like manner (this is illustrated in FIGS. 6 to 8). The same applies to As is apparent from FIG. 5, the main fuel injection is divided into two split injections, whereby the peak value of the heat generation rate is reduced and the engine vibration is reduced. By setting the number of split injections to a minimum of 2 and increasing the injection amount of the first stage split injection more than the pre-injection amount, it is possible to set the end timing of split injection to an earlier time. This is preferable for suppressing smoke and securing torque.

FIG. 6 shows a case where the main fuel injection is divided into three divided injections, and the injection amount of the second-stage divided injection is larger than the injection amount of the first-stage divided injection and the second-stage divided injection The injection amount of the third stage divided injection is made smaller than the injection amount of the injection. In this case, the peak value of the heat generation rate is further smaller than in the case of the two-stage split injection in FIG. 5, and the engine vibration is further reduced.

FIG. 7 shows a case where the main fuel injection is divided into four divided injections. The injection amount is increased until the third-stage divided injection, and the injection amount of the fourth-stage divided injection is made smaller than the injection amount of the third-stage divided injection. Also in this example, the peak value of the heat generation rate is made sufficiently small, and the engine vibration is sufficiently reduced. FIG. 8 shows a case where the main fuel injection is divided into five divided injections. The injection amount increases until the third-stage divided injection, and after the fourth-stage divided injection, the injection amount decreases. Also in this example, the peak value of the heat generation rate is made sufficiently small, and the engine vibration is sufficiently reduced.

FIG. 9 shows the vibration level in each part of each of the mount members 1M, 3M, 4M in FIG. 1 when the number of divided injections is 2 to 5 as described above. In this case, the main fuel injection is performed only once. The three-axis sum shown in FIG. 9 indicates the total sum of vibration energy in the three-axis directions (front and rear, left and right, and top and bottom) at each of the mount members 1M, 3M, and 4M. It is understood that in the case where the main fuel injection is divided injection, the vibration is reduced as compared with the case of Base. Note that a reduction of 1 db in the vibration level is a considerably large vibration reduction, and the effect of reducing the engine vibration is also great by using two split injections. Needless to say, the effect of reducing the vibration when the divided injection of three or more stages is used is extremely great. As the number of divided injections is increased, the injection timing of the subsequent divided injection is delayed and the occurrence of smoke becomes a problem. However, the fuel injection valve 10 having good responsiveness and high injection amount accuracy is used. Thus, it is possible to suppress the smoke by advancing the injection timing of the final divided injection.

Here, in the region where the main fuel injection is divided injection for engine vibration reduction, supercharging is performed, which is extremely preferable in terms of securing torque. In particular, the fuel injection amount can be increased according to supercharging, which is preferable in terms of torque improvement. However, it is preferable to increase the fuel injection amount that is increased in supercharging when the excess air ratio λ of the intake air is 1 or more (smoke suppression). The interval between the divided injections of each stage is shorter than the interval between the divided injections of the first stage and the pre-injection, so that the time until the completion of all the divided injections is accelerated as much as possible to secure torque and suppress smoke. Is preferable. Further, by increasing the injection amount of the first-stage divided injection more than the pre-fuel injection amount, it is possible to perform combustion mainly using diffusion combustion. In a high load / high speed range where engine vibration is not a problem, the main fuel injection is performed once to ensure torque.

 Although the embodiment has been described above, the present invention is not limited to the embodiment, and can be appropriately changed within the scope described in the scope of claims. For example, the invention includes the following cases. . The vehicle is not limited to an automobile, but may be a two-wheeled vehicle or a vehicle (so-called train) traveling on a track (rail). The vehicle exhaust turbo supercharger may be one or may not have the exhaust turbo supercharger. The pre-fuel injection may not be performed (particularly, the pre-fuel injection is not performed when the geometric compression ratio of the engine is a high compression ratio exceeding, for example, 15). A sensor for detecting the vibration of the engine mount portion may be provided, and the split injection of the main fuel injection may be executed on condition that the detected vibration is equal to or greater than a preset threshold value. Of course, the object of the present invention is not limited to what is explicitly stated, but also implicitly includes providing what is substantially preferred or expressed as an advantage.

 The present invention is suitable for application to, for example, a diesel engine mounted on an automobile.

1: Engine 5: Combustion chamber 6: Intake port 7: Exhaust port 10: Fuel injection valve 20: Intake passage 22, 23: Exhaust turbo type supercharger 30: Exhaust passage U controller

Claims (5)

In a fuel injection control device for a vehicle-mounted diesel engine that is mounted on a vehicle and supplied with fuel mainly composed of light oil,
In at least the low speed region of the engine high load region, the main fuel injection for diffusion combustion is divided injection that is performed in a plurality of times,
The injection amount of the second stage split injection is greater than the injection quantity of the first stage split injection ,
The geometric compression ratio of the engine is 15 or less,
Pre-fuel injection for premixed combustion is performed before the main fuel injection in at least a low speed region of the engine high load region,
The divided injection is made 3 times or more,
The injection amount of the last stage in the divided injection is made smaller than the injection quantity of the divided injection of the immediately preceding stage,
The injection amount in each of the three or more divided injections is changed so that the injection amount is initially increased, and thereafter, the injection amount is changed so as to be reduced.
When the injection amount is changed so as to be increased by the divided injection, the injection amount in the divided injection executed before is 50 to 75% of the injection amount in the immediately following divided injection,
When it is changed so that the injection amount is reduced by the divided injection, the injection amount in the divided injection executed later is 85 to 90% of the injection amount in the immediately preceding divided injection.
A fuel injection control device for a vehicle-mounted diesel engine. Oite to claim 1,
In at least a low speed range of the engine high load region, the supercharging is performed,
A fuel injection control device for a vehicle-mounted diesel engine. In claim 1 or claim 2 ,
A distance between the second-stage split injection before and Symbol 1-stage split injection is shorter than the distance between the first-stage split injection and the pre-fuel injection,
A fuel injection control device for a vehicle-mounted diesel engine. In any one of Claims 1 thru | or 3 ,
Supercharging is performed at least in the low speed range of the engine high load range,
In accordance with the increase in the intake charge amount due to the supercharging, the fuel injection amount is increased in a range where the excess air ratio λ is 1 or more.
A fuel injection control device for a vehicle-mounted diesel engine. In any one of Claims 1 thru | or 4 ,
A fuel injection control device for a vehicle-mounted diesel engine, wherein the main fuel injection is performed in one stage without being divided in a high speed region of an engine high load region.

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