JP2009085117A - Control device of diesel engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To lower the maximum value (Pmax) of cylinder internal pressure in a direct injection type diesel engine, to decrease weight, and to suppress the degradation of output. <P>SOLUTION: When an operation state of an engine 1 is in a first area (I) on a high load side, fuel is jetted by an injector 5 in a pattern wherein a fuel injection rate is increased with the expansion of a combustion chamber capacity in an expanding stroke of a cylinder 2 at least in a middle period of a fuel injection. Abrupt starting of initial combustion is thereby suppressed to make the maximum value (Pmax) in the cylinder internal pressure lower than a conventional one, and the lowering of the cylinder internal pressure due to the expansion of the combustion chamber capacity is suppressed from the middle period to a latter period of combustion. The lowering of output of the engine 1 is then suppressed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a control device for a direct injection diesel engine, and particularly relates to the technical field of variable injection rate control by precise operation control of a fuel injection valve.

  Conventionally, a diesel engine generally ignites fuel by compression of a cylinder, so that a compression ratio is higher than that of a spark ignition engine, and a maximum value (Pmax) of a cylinder internal pressure that is increased by combustion is considerably high. For this reason, piston blocks and connecting rods as well as cylinder blocks and cylinder heads become relatively heavy when trying to secure their strength and rigidity, which is disadvantageous in terms of fuel consumption and mobility when mounted on a vehicle. May be.

On the other hand, for example, in Patent Document 1, the mechanical compression ratio of the cylinder is lowered, and the effective compression ratio (actual compression ratio of the air filled in the cylinder) can be adjusted by incorporating a variable valve mechanism. The diesel engine is described. By adjusting the effective compression ratio, it is possible to ensure engine startability and enhance combustibility at low and medium loads, and to suppress an increase in cylinder pressure at high loads and reduce the load on each part of the engine. It is possible to reduce the weight.
JP 2003-120368 A

  However, in the conventional example, the effective compression ratio is reduced in order to suppress an increase in the cylinder internal pressure when the engine is heavily loaded, and it is inevitable that the output is reduced due to a reduction in the intake charge efficiency of the cylinder. .

  The present invention has been made in view of such a point, and an object of the present invention is to reduce the maximum value (Pmax) of the cylinder internal pressure in a direct injection type diesel engine and to reduce the weight thereof. This is to suppress a decrease in output due to.

  In order to achieve the above-mentioned object, the present invention is devised in the manner of fuel injection directly into the combustion chamber so that the increase in the cylinder pressure due to the combustion is reduced by the expansion of the cylinder volume in the expansion stroke. Thus, the maximum value (Pmax) of the cylinder internal pressure is reduced.

  Specifically, the control device for a diesel engine according to the invention of claim 1 includes a fuel injection valve that directly injects fuel into a combustion chamber in a cylinder, and a fuel injection pattern by the fuel injection valve at least in a fuel injection period. In the middle period, an injection pattern setting means for setting a rising injection pattern in which the fuel injection rate increases as the combustion chamber volume in the expansion stroke of the cylinder increases, and a rising injection pattern set by the injection pattern setting means. And an injection control means for operating the fuel injection valve. The middle period of the fuel injection period may be the middle period of the period in which fuel is injected from the fuel injection valve divided into three equal parts, the first period, the middle period, and the second period.

  With the above configuration, when the fuel injection valve is controlled by the injection control means so that the fuel rising injection pattern is set by the injection pattern setting means during the operation of the diesel engine, The injection rate of the directly injected fuel increases as the combustion chamber volume increases in the expansion stroke of the cylinder, and the heat generation rate due to the combustion also increases gradually as the combustion chamber volume increases.

  According to such a rising heat generation pattern, the rapid increase in the cylinder pressure near the top dead center of the cylinder is alleviated, while the decrease in the cylinder pressure due to the expansion of the combustion chamber volume is suppressed. Compared to conventional general combustion, the cylinder internal pressure is “highly stopped”, so that the pressure can be efficiently converted into the rotational force of the crankshaft. Therefore, while decreasing the maximum value (Pmax) of the cylinder internal pressure, it is possible to sufficiently suppress the decrease in output.

  As the rising injection pattern that can obtain the above-described effect, it is preferable that the combustion is performed so that the maximum value (Pmax) of the cylinder pressure that rises due to combustion does not exceed a predetermined multiple of the cylinder pressure at the compression top dead center. The degree of increase in the fuel injection rate is set in association with the rate of expansion of the chamber volume (Claim 2), and the predetermined multiple is approximately 1.0, that is, the maximum value (Pmax) of the cylinder internal pressure is It is preferable not to exceed the cylinder internal pressure at the compression top dead center.

  More preferably, the cylinder pressure is included in a range of approximately 0.9 to 1.0 times the maximum value (Pmax) over a period from the vicinity of compression top dead center to a predetermined crank angle (for example, about ATDC 30 ° CA). Thus, the degree of increase in the fuel injection rate is set in association with the expansion ratio of the combustion chamber volume (Claim 3), and in this way, the cylinder pressure is approximately in the vicinity of the maximum value in the period up to the predetermined crank angle. Therefore, a decrease in engine output can be effectively suppressed.

  By the way, in an operating state where the engine load is not very high, the intake charge efficiency of the cylinder is originally lowered or the fuel injection amount is reduced. Therefore, the fuel injection valve is opened at a stroke as usual to inject fuel. However, the maximum value (Pmax) of the cylinder pressure does not reach the allowable upper limit value (hereinafter referred to as a normal injection pattern).

  Therefore, it is preferable to set the rising injection pattern in the operation region on the relatively high load side (Claim 4), while injecting the fuel in the normal injection pattern in the operation region on the relatively low load side. Is to do so. By so doing, fuel is injected in a relatively short period of time with a normal injection pattern, so that the thermal efficiency is improved by shortening the combustion period, and fuel consumption is reduced.

  Further, the degree of increase in the fuel injection rate in the rising injection pattern is not necessarily constant, and may be changed according to, for example, the operating state (load, rotation speed, etc.) of the engine (claim 5). . By so doing, it is possible to more effectively suppress a decrease in engine output.

  Here, in order to realize the fuel injection pattern that rises as described above, for example, the fuel injection valve is assumed to be capable of variably adjusting the opening area of the injection port due to the opening operation of the core valve. The opening speed of the nozzle hole may be adjusted (claim 6). That is, if the nozzle is opened at the maximum opening speed to the maximum opening area and the fuel is injected all at once, the normal injection pattern is obtained, and the opening area is gradually reduced at a predetermined rate by intentionally reducing the opening speed. If the fuel injection rate is increased, a rising injection pattern in which the fuel injection rate gradually increases can be realized.

  As described above, according to the control device of the present invention, the injection mode of the fuel that is directly injected into the combustion chamber in the cylinder is changed to the rising injection in which the injection rate gradually increases at a predetermined rate during the injection period. By making the pattern, the rise of the cylinder pressure in the early stage of combustion is suppressed, and the fall of the cylinder pressure due to the expansion of the combustion chamber volume is suppressed from the middle to the later stage of combustion. Can be made. Therefore, the reduction in the output can be sufficiently suppressed while reducing the maximum value (Pmax) of the cylinder internal pressure and making the engine lighter.

  Also, in the low load side operation region where the maximum value (Pmax) of the cylinder internal pressure does not become so high, the fuel injection valve is opened at once to inject fuel as usual, thereby reducing fuel consumption by shortening the combustion period. It is done.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. It should be noted that the following description of the preferred embodiment is merely illustrative in nature, and is not intended to limit the present invention, its application, or its use.

FIG. 1 shows an example of a diesel engine control device A according to an embodiment of the present invention. Reference numeral 1 denotes a diesel engine mounted on a vehicle. This engine 1 has a plurality of cylinders 2, 2,... (Only one is shown), and in each cylinder 2, a combustion chamber 4 is defined above the piston 3 inserted and inserted. The volume of the combustion chamber 4 is changed by the reciprocating motion of the piston 3, and the volume ratio between when it is at the top dead center and when it is at the bottom dead center becomes a mechanical compression ratio.

  The cylinder head of the engine 1 is provided with an injector 5 (fuel injection valve) for each cylinder 2 so that fuel is directly injected into the combustion chamber 4. Although not shown in detail, the injector 5 lifts the core valve by a piezo actuator, and is disposed with the front nozzle hole facing the ceiling of the combustion chamber 4. The piezo-actuator changes the driving amount (lift amount) of the core valve according to the applied voltage, and the opening area of the nozzle hole by this core valve can be changed.

  The injector 5 is connected to a common rail (not shown) common to all the cylinders 2, 2,..., And can inject high-pressure fuel stored therein at an arbitrary timing. The common rail is provided with a sensor that detects an average pressure (common rail pressure) of the fuel inside the common rail, and a signal from this sensor is input to an ECU 30 described later so that the common rail pressure is controlled accordingly. It has become.

  In addition, an intake port 6 and an exhaust port 7 are formed for each cylinder 2 in the cylinder head of the engine 1 and open to the ceiling of the combustion chamber 4. An intake valve 8 and an exhaust valve 9 are individually provided at the opening ends of the intake port 6 and the exhaust port 7, and although not shown, the intake port 6 and the exhaust port are driven by a valve mechanism such as a camshaft. Each of the ports 7 is opened and closed at a predetermined timing.

  Thus, the other end of the intake port 6 whose one end opens into the combustion chamber 4 opens to one side (right side in the drawing) of the cylinder head of the engine 1 and communicates with the intake passage 10. The intake passage 10 is for supplying air (fresh air) to the combustion chamber 4 of each cylinder 2. The intake passage 10 is driven by a turbine 16, which will be described later, and compresses the intake air, and is compressed by the compressor 11. An intercooler 12 that cools intake air and an intake throttle valve 13 that is a butterfly valve are arranged in order from the upstream side.

  On the other hand, an exhaust passage 15 for discharging burned gas from the combustion chamber 4 of each cylinder 2 is connected to the opposite side (left side in the figure) of the engine 1. The upstream end of the exhaust passage 15 is an exhaust manifold that branches into each cylinder 2 and communicates with the exhaust port 7 respectively. Downstream of the exhaust manifold 15 is a turbine 16 that is rotated by receiving an exhaust flow, A diesel oxidation catalyst 17 capable of purifying harmful components (HC, CO, soot, etc.) and a catalyzed DPF (Diesel Particulate Filter) 18 are sequentially arranged from the upstream side.

  The turbine 16 and the compressor 11 are mechanically connected to form a turbocharger 20, and in this embodiment, the cross-sectional area of the exhaust gas to the turbine 16 is changed by the movable flaps 21, 21,. The variable turbocharger (Variable Geometry Turbosupercharger: hereinafter referred to as VGT) is used.

  Further, the exhaust passage 15 is connected to an upstream end of an exhaust recirculation passage 22 (hereinafter referred to as an EGR passage) that opens toward a collecting portion of the exhaust manifold and recirculates a part of the exhaust to the intake side. The downstream end of the EGR passage 22 is connected to the intake passage 10 on the downstream side of the intake throttle valve 13 so as to introduce recirculated exhaust gas (hereinafter referred to as EGR gas) into the intake passage 10. An electromagnetic valve 23 (hereinafter referred to as an EGR valve) for adjusting the flow rate of EGR gas is disposed in the middle of the EGR passage 22.

  The injector 5, the intake throttle valve 13, the VGT 20, the EGR valve 23, etc. are all operated in response to a control signal from a control unit (Electronic Control Unit: hereinafter referred to as ECU) 30. The ECU 30 receives at least signals from a crank angle sensor 31, an air flow sensor 32, an intake pressure sensor 33, an intake air temperature sensor 34, and the like, and further includes a linear O2 sensor 35 for detecting an oxygen concentration in the exhaust, and an illustrated figure. A signal from an accelerator opening sensor 36 that detects the amount of depression of the accelerator pedal (accelerator opening) is also input.

(Engine combustion control)
The basic control of the engine 1 by the ECU 30 is to determine a target torque (target load) mainly based on the accelerator opening, and to control the fuel injection amount and injection timing corresponding to the target torque by operating the injector 5. It is realized. Further, the recirculation ratio (EGR ratio) of the exhaust gas to the combustion chamber 4 is controlled by controlling the opening degree of the intake throttle valve 13 and the EGR valve 23, and the supercharging efficiency of the intake air is controlled by controlling the flaps 21, 21,. I try to increase it.

  Further, as a feature of the present invention, in this embodiment, the operation control of the injector 5 is made particularly precise, and the fuel injection rate in one injection period is variably controlled. That is, in the operation region on the relatively low load side, the normal injection pattern in which the core valve is opened at once to inject fuel is used, whereas in the operation region on the relatively high load side, the opening speed of the core valve is intentionally slow. Thus, a rising injection pattern in which the fuel injection rate gradually increases is obtained.

  In the following, a normal fuel injection pattern and a fuel injection pattern which is a feature of the present invention, and a combustion state in which the maximum value (Pmax) of the cylinder pressure is relatively low (hereinafter also referred to as low Pmax combustion) will be described. This will be explained in comparison with the above.

  First, in general, in a direct injection type diesel engine, fuel is injected from the vicinity of top dead center (TDC) to the expansion stroke into the combustion chamber in the cylinder that has become high temperature and high pressure at the end of the compression stroke. Then, the fuel spray injected in the initial stage is ignited after a slight time delay, and it is supplied one after another so that surrounding air and fuel spray are caught in the flame kernel formed thereby, so that a state of so-called diffusion combustion is achieved. Become.

  In order to improve the diesel combustion mainly composed of diffusion combustion, the normal injection pattern that is more general than the conventional one is to open the injector nozzle at a predetermined injection timing and inject fuel at a predetermined injection timing. The fuel injection rate in this case becomes substantially constant after suddenly rising to the maximum value as shown by the broken line in FIG. 2 (a), and once again after the injection period (crank angle period) corresponding to the required injection amount elapses. Draw a rectangular graph that falls.

  In such a normal injection pattern, the initial premixed combustion after the ignition delay becomes intense, so that the heat generation rate rises sharply immediately after TDC as shown by the broken line in FIG. Due to the heat generation due to this, the cylinder internal pressure suddenly increases. That is, as shown in FIG. 3C, the cylinder internal pressure rises further from the peak due to cylinder compression (near TDC) and reaches the maximum value (Pmax), and then the combustion chamber volume increases in the expansion stroke of the cylinder. Along with this, it begins to decrease quickly.

  If it is attempted to increase the engine output (torque) in such a conventional combustion state, the charging efficiency will be increased or the fuel injection amount will be increased. Since the entire cylinder internal pressure waveform increases and the maximum value (Pmax) also increases, the strength and rigidity of the cylinder block, cylinder head, piston 3, connecting rod, etc. are increased to withstand this. Inevitably, an increase in weight is inevitable.

  On the other hand, in the fuel injection pattern that rises as a feature of the present invention, the core valve of the injector is intentionally slowly opened and gradually opened at a predetermined rate over a period from the vicinity of TDC to a predetermined crank angle. Increase the area. In this way, as shown by the solid line in FIG. 2 (a), the fuel injection rate gradually rises from the vicinity of the TDC, rises upward at a predetermined rate corresponding to the expansion of the combustion chamber volume, and then decreases at a stretch. Draw a graph.

  Even in such a rising injection pattern, as in the normal injection pattern, the fuel spray starts premixed combustion after the ignition delay, but the initial combustion is very little, so As shown by the solid line in Fig. (B), the rise of the heat generation rate becomes very gradual. As described above, as the fuel injection rate increases, the heat generation rate due to combustion also increases.

  In particular, in this embodiment, the degree of increase in the fuel injection rate in the above-described rising injection pattern is set to an optimum value in advance by experiments or the like in association with the rate of expansion of the combustion chamber volume in the cylinder expansion stroke. . That is, in the expansion stroke of the cylinder, the cylinder internal pressure tends to gradually decrease due to the expansion of the combustion chamber volume. In this embodiment, as described above, the combustion chamber has a heat generation rate that rises upward. The effect of expanding the volume is counteracted.

  For this reason, as shown by the solid line in FIG. 3C, the cylinder pressure does not rise from the peak due to cylinder compression (near TDC) as in the normal injection pattern, but from a predetermined crank angle (in the example shown in the figure) from the vicinity of TDC. Over a period up to about ATDC 30 ° CA). In other words, in the combustion with the rising injection pattern, the cylinder pressure does not reach the peak due to the combustion as in the normal injection pattern, and the maximum value (Pmax) is substantially the same as the peak value due to the compression.

  In this way, the maximum value (Pmax) of the cylinder internal pressure becomes lower than that of the conventional general diesel combustion, while in the low Pmax combustion of this embodiment, the cylinder internal pressure is kept at a high level to some extent (highly stopped). Since the period becomes longer, the pressure can be efficiently converted into the rotational force of the crankshaft, and the decrease in output can be effectively suppressed. In FIG. 2C, the charging efficiency in normal combustion (broken line graph) is set slightly higher so that the two graphs can be easily compared.

(Specific control procedure)
Next, the procedure of fuel injection control by the ECU 30 will be described more specifically with reference to the flowchart shown in FIG.

  First, in step S1 after the start, signals from various sensors 31 to 36 are input, and in the subsequent step S2, a target torque and an engine rotation speed are calculated. The engine speed is calculated based on a signal from the crank angle sensor 31, and the target torque is read from a map (not shown) stored in advance in the ECU 30 based on the engine speed and the accelerator opening. The map is set so that the target torque increases as the accelerator opening increases and as the engine speed increases.

  In step S3, based on the target torque and engine rotation speed obtained in step S2, the first state (I ). This control map is divided into a first region (I) in which the operating region of the engine 1 is normally combusted on a relatively low load side and a second region (II) in which a low Pmax combustion is performed on a relatively high load side. If the operating state of the engine 1 is in the second region (II), the determination is NO and the process proceeds to step S7, which will be described later, whereas if it is in the first region (I), the determination is YES and the process proceeds to step S4. move on.

  Here, in the control map, in the first region (I), a target fuel injection amount and injection timing are set in association with the load state (target torque) and the rotational speed of the engine 1, and a normal injection pattern is set. The drive pulse signal of the injector 5 is a rectangular wave as schematically shown in the lower right side of the figure. On the other hand, in the second region (II), the core valve is opened so that the fuel rising injection pattern including information on the target injection amount and the injection timing, that is, the injection rate gradually increases at a predetermined rate during the injection period. A triangular drive pulse waveform in which the speed is set is set in association with the load state and the rotation speed of the engine 1.

  Specifically, even in the second region (II), particularly in the full load region (region above the broken line), fuel is injected in a lump pattern as shown in the upper right side of the figure, while the cylinder internal pressure due to compression is injected. Except for the full load range where the peak of the engine does not become so high (below the broken line), a small amount of fuel is pre-injected before the TDC as shown in the middle stage on the right side, and the cylinder pressure is increased by the combustion in advance, and the rising pattern The main injection is performed. Note that the boundary between the first region (I) and the second region (II) is on the low speed side and on the higher load side than the high speed side as shown in the drawing in consideration of the supercharging state and exhaust purification performance of the engine 1. It is set to be.

  Then, in step S4, which proceeds with the determination that the engine is in the first region (I), the target injection of fuel by the injector 5 from the control map is performed based on the target torque and engine speed determined in step S2. The quantity and the injection timing are read and set, respectively. At this time, it can be said that the drive pulse signal of the injector 5 becomes a rectangular wave in the normal injection pattern, and the target value of the fuel injection rate is the maximum value. The pulse width becomes a length (crank angle period) corresponding to the required injection amount.

  In the following step S5, it is determined whether or not the injection timing set in step S4 has been reached based on the crank angle signal. If this determination is NO and the injection timing is not reached, the process waits. If the injection timing is reached, the determination is YES. In step S6, a rectangular-wave drive pulse signal is output to operate the injector 5. That is, a predetermined maximum voltage is applied to the injector 5 to open the core valve at the maximum speed, fuel is injected from the injection port at once, and then the process returns.

  In other words, in the first region (I) on the low load side where the maximum value (Pmax) of the cylinder internal pressure does not become so high, the conventional normal injection pattern is used, and the injection port of the injector 5 is opened at once to inject fuel. As a result, the fuel can be blown out in a relatively short injection period, the thermal efficiency is improved by shortening the combustion period, and fuel consumption is reduced.

  On the other hand, in step S7, which has proceeded after determining that the engine 1 is in the second region (II) in step S3 (NO), the control of FIG. 4 is performed based on the target torque and engine speed determined in step S2. A rising fuel injection pattern by the injector 5 from the map, that is, a triangular drive pulse signal that gradually increases the fuel injection rate at a predetermined rate during the injection period (setting of the target injection pattern) is read.

  Subsequently, in step S8, based on the crank angle signal, it is determined whether or not the injection timing set in step S7 has been reached. If this determination is NO and the injection timing is not reached, the process waits. The process proceeds to step S9, and a triangular drive pulse signal is output to operate the injector 5 so that the rising injection pattern is obtained, and then the process returns.

  Thus, in the injector 5 that has received the triangular drive pulse signal, the deformation amount of the piezo actuator gradually increases in response to the gradually increasing applied voltage, thereby driving the core valve and driving the nozzle hole. Since the open area gradually increases at a predetermined rate, the fuel injection pattern rises as described above with reference to FIG. 2, and the characteristic low Pmax combustion state of the present invention is achieved.

  That is, in the second region (II) on the high load side, the maximum value (Pmax) of the cylinder internal pressure becomes too high in the normal injection pattern, and there is a possibility that an excessive load is applied to each part of the engine 1. In some cases, a low Pmax combustion state with a rising injection pattern is used to ensure the reliability of each part of the engine while suppressing a decrease in output.

  When the operating state of the engine 1 is in the second region (II) on the relatively high load side by the steps S4 and S7 of the flow, the fuel injection pattern by the injector 5 is changed to the cylinder at least in the middle period of the fuel injection period. The injection pattern setting means 30a is configured to set a rising injection pattern in which the fuel injection rate increases with the expansion of the combustion chamber volume in the second expansion stroke.

  The rising injection pattern is that the combustion chamber volume expands in the expansion stroke of the cylinder 2, while the heat generation rate due to combustion increases in a rising manner, so that the cylinder internal pressure is increased over a period from the vicinity of the TDC to a predetermined crank angle. The injection rate is set to be gradually increased at a predetermined rate corresponding to the expansion rate of the combustion chamber volume so as to be maintained substantially constant. The injection pattern setting means 30a sets a normal injection pattern in the first region (I) on the relatively high load side.

  Further, the steps S8 and S9 of the flow constitute the injection control means 30b that operates the injector 5 so as to have the rising injection pattern set as described above. The injection control means 30b adjusts the opening speed of the injection port by controlling the operation of the core valve of the piezo injector 5 to realize the upward injection pattern.

  The functions of the injection pattern setting means 30a and the injection control means 30b are realized by the CPU of the ECU 30 executing a control program as shown in the flow of FIG. In this sense, it can be said that the ECU 30 includes the above-described units in the form of a software program.

  Therefore, according to the control apparatus A for a diesel engine according to this embodiment, fuel is injected by the injector 5 in the relatively high-load operation region (first region (I)), and the characteristic rising injection pattern of the present invention. By suppressing the sudden rise of the initial combustion and lowering the maximum value (Pmax) of the cylinder pressure from the conventional level, the decrease in the cylinder pressure due to the expansion of the combustion chamber volume is suppressed from the middle to the latter half of the combustion. Thus, the cylinder internal pressure can be “highly stopped”, and thereby a decrease in the output of the engine 1 can be suppressed.

  In particular, in this embodiment, the degree of increase in the injection rate in the rising injection pattern is optimally set in association with the rate at which the volume of the combustion chamber 4 expands in the expansion stroke of the cylinder 2, so that the cylinder pressure is increased. Since it is maintained substantially constant over a period from the vicinity of the TDC to a predetermined crank angle, the cylinder internal pressure can be efficiently converted into the rotational torque of the crankshaft, and the output reduction of the engine 1 is effectively suppressed. it can.

  If the maximum value (Pmax) of the cylinder internal pressure in the high load range can be reduced, the strength and rigidity of the cylinder block and cylinder head of the engine 1 as well as the piston 3 and the connecting rod are not increased so much. The engine 1 can be reduced in weight.

(Other embodiments)
In addition, the control apparatus of the diesel engine which concerns on this invention is not limited to above-described embodiment, It includes other various structures. That is, for example, in the above embodiment, as the fuel injection pattern that rises, the degree of increase in the fuel injection rate is set so that the cylinder internal pressure becomes substantially constant over a period from the vicinity of TDC to a predetermined crank angle. For example, the in-cylinder pressure may be included in the range of about 0.9 to 1.0 times the maximum value (Pmax) in the above period.

  Furthermore, it is only necessary to set the degree of increase in the fuel injection rate so that the maximum value (Pmax) of the cylinder pressure that rises due to combustion does not exceed a predetermined multiple of the peak value (value at TDC) of the cylinder pressure due to compression. . The predetermined multiple may be set according to the engine specifications, for example, 1.1 times, but is preferably set to approximately 1.0 times so that the maximum value (Pmax) does not exceed the cylinder pressure at TDC. Is to do.

  Further, in the above-described embodiment, the degree of increase in the injection rate in the fuel injection pattern that rises is changed according to the operating state such as the load and rotation speed of the engine 1, but the present invention is not limited to this.

  Furthermore, in the low load side operation region (first region (I)) that does not have a rising fuel injection pattern in the above-described embodiment, fuel is injected in the intake or compression stroke of the cylinder 2, and after premixing, compression ignition is performed. (So-called HCCI, PCCI) may be used.

  In addition, the configuration of the diesel engine 1 to which the present invention can be applied is not limited to that of the above-described embodiment, and can be applied to, for example, a configuration that does not include the turbocharger 20.

  As described above, the present invention can be reduced in weight without significantly reducing the maximum output of the direct injection diesel engine, and thus is particularly suitable for mounting in an automobile, for example.

1 is an overall configuration diagram of a control device for a diesel engine according to an embodiment of the present invention. FIG. 4 is an explanatory view showing a fuel injection pattern (a) that rises in comparison with a normal injection pattern, a change (b) in the heat generation rate due to combustion, and a change (c) in the cylinder pressure. It is a flowchart figure which shows the procedure of fuel injection control. It is explanatory drawing which shows an example of the control map which divided | segmented the driving | operation area | region of the engine into two and each set the fuel injection quantity, the injection pattern, etc.

Explanation of symbols

A Diesel engine control device 1 Engine 2 Cylinder 4 Combustion chamber 5 Injector (fuel injection valve)
30 Controller 30a Injection pattern setting means 30b Injection control means

Claims (6)

A fuel injection valve that directly injects fuel into the combustion chamber in the cylinder;
An injection pattern setting means for setting the fuel injection pattern by the fuel injection valve to a rising injection pattern in which the fuel injection rate increases as the combustion chamber volume increases in the expansion stroke of the cylinder, at least in the middle of the fuel injection period;
Injection control means for operating the fuel injection valve so as to have a rising injection pattern set by the injection pattern setting means;
A control device for a diesel engine, comprising:   The rising injection pattern is the degree of increase in the fuel injection rate in association with the expansion ratio of the combustion chamber volume so that the maximum value of the cylinder pressure that rises due to combustion does not exceed a predetermined multiple of the value at the compression top dead center The diesel engine control device according to claim 1, wherein:   The rising injection pattern corresponds to the expansion ratio of the combustion chamber volume so that the cylinder internal pressure is in the range of about 0.9 to 1.0 times the maximum value from the vicinity of the compression top dead center to the predetermined crank angle. The control device for a diesel engine according to claim 2, wherein the increase degree of the fuel injection rate is set.   The diesel engine control device according to any one of claims 1 to 3, wherein the injection pattern setting means sets a trailing injection pattern in an operation region on a relatively high load side.   The diesel engine control device according to any one of claims 1 to 4, wherein the injection pattern setting means changes the degree of increase in the fuel injection rate in the rising injection pattern according to the operating state of the engine. The fuel injection valve can variably adjust the opening area of the nozzle hole due to the opening operation of the core valve.
6. The diesel engine according to claim 1, wherein the injection control means adjusts the opening speed of the injection hole by controlling the operation of the core valve to realize a rising injection pattern set by the injection pattern setting means. Engine control device.

Images