Patent Application
20220003147
The present invention relates to a subchamber diesel engine having a main combustion chamber and a combustion subchamber that communicates by a communication hole.
Conventionally, a subchamber diesel engine having a main combustion chamber and a combustion subchamber that communicates by a communication hole has been known.
A general vortex chamber type subchamber diesel engine includes a main combustion chamber formed on a piston, a combustion subchamber that communicates with the main combustion chamber by a communication hole and an injector that injects fuel into the combustion subchamber, and air enters the combustion subchamber from the main combustion chamber side through the communication hole in a compression stroke and generates a strong vortex flow in the combustion subchamber. Then, fuel is injected into the combustion subchamber where the vortex flow is generated from the injector arranged so as to face the combustion subchamber so as to form an air-fuel mixture, and compression self-ignition is performed in the vicinity of a compression top dead center so as to start combustion. Next, combustion energy of combustion gas generated in the combustion subchamber causes the combustion gas to enter the main combustion chamber from the combustion subchamber through the communication hole, completes combustion while driving the piston, and obtains power (For example, see Patent Literature 1 and Patent Literature 2).
In the subchamber diesel engine described in Patent Literature 1, in order to improve the combustion of the subchamber diesel engine, two injectors facing the combustion subchamber are arranged, and fuel is injected a first time toward a wall surface of the combustion subchamber from a latter half of an intake stroke to a first half of the compression stroke and then, second fuel is injected into the combustion subchamber from the latter half of the compression stroke to the first half of the expansion stroke so as to improve the combustion.
Further, in the subchamber diesel engine described in Patent Document 2, in order to suppress inhibition of the air-fuel mixture formation due to the preliminary injection from the injector facing the combustion subchamber, in a starting region, emission of unburned fuel and unburned gas is reduced by not performing the preliminary injection.
PTL 1: Japanese Unexamined Patent Application No. Hei 7-116941
PTL 2: Japanese Patent No. 3851727
As described above, by performing preliminary injection in the subchamber diesel engine, so-called premixed compression self-ignition combustion, in which an air-fuel mixture is formed in advance and compression self-ignition is performed, can be performed. However, when the premixed compression self-ignition is performed, ignition timing of the fuel may be too early and thermal efficiency may be significantly lowered depending on an operation condition. Therefore, it has been proposed to delay the ignition timing by using a fuel that is difficult to be self-ignited or by lowering a compression ratio. However, changing the fuel or lowering the compression ratio of the engine leads to narrowing of the conditions for employing the engine and lowering performance of the engine, and that cannot be easily employed. Further, when the preliminary injection is performed, it is considered to finely change the injection conditions for injecting fuel into the combustion subchamber so that appropriate combustion is performed, but in the conventional subchamber diesel engine described in Patent Literature 1 and Patent Literature 2, a mechanical jerk-type fuel injection device is employed, and since fuel injection characteristics are controlled by a rotation speed of the engine, they cannot be changed freely, and optimal fuel injection control according to the operation condition cannot be implemented.
The present invention has been made in view of the above facts, and its main technical problem is to provide a subchamber diesel engine which has excellent thermal efficiency and can appropriately control the ignition timing of the fuel supplied to the combustion subchamber.
In order to solve the above-mentioned main technical problem, according to the present invention, provided in a subchamber diesel engine including a main combustion chamber and a combustion subchamber that communicates by a communication hole, is a subchamber diesel engine, a subchamber diesel engine including an electrically driven injector that injects fuel to the combustion subchamber at arbitrary timing, a fuel passage pipe connected to a fuel inlet of the injector, a fuel pump that supplies fuel to the fuel passage pipe, an engine operation state detector that detects the engine operation state, and a controller, in which the controller performs a preliminary injection of fuel in a first half of an intake stroke, performs a main injection during a compression stroke, and performs injection for ignition control in the vicinity of the compression top dead center, after the main injection.
A spray center axis of the fuel injected from the injector and a hole center axis of the communication hole are preferably offset. Further, a glow plug is arranged in the combustion subchamber, and when an exhaust temperature detected by the operation state detector is equal to or lower than a predetermined temperature, it is preferable that the controller does not perform the preliminary injection but operates the glow plug so as to heat the combustion subchamber.
Further, the controller controls injection start timing, an injection amount, and an injection pressure of the main injection injected from the injector on the basis of the operation state detected by the operation state detector, and it is preferable to divide the main injection into a predetermined number of times and inject the main injection in accordance with the injection amount of the main injection and the injection pressure required at that time calculated by the controller. The controller may advance injection start timing of the main injection from a top dead center side of the compression stroke to a bottom dead center side as the engine rotation speed detected by the operation state detector changes from low rotation to high rotation. Further, the injection pressure injected from the injector is preferably set between 8 MPa and 40 MPa.
According to the diesel engine of the present invention, a subchamber diesel engine having excellent thermal efficiency and can appropriately control ignition timing of the fuel supplied to the combustion subchamber is provided.
A preferred embodiment of a subchamber diesel engine configured in accordance with the present invention will be described below with reference to the accompanying drawings.
The engine main body 2 includes a cylinder block 3, a cylinder head 4, a piston 5, an intake port 6, an intake valve 7, an exhaust port 8 (indicated by a broken line), and an exhaust valve (not shown). The exhaust valve is arranged in parallel with the intake valve 7 in a direction perpendicular to the paper surface and is opened and closed together with the intake valve 7 by a valve operating mechanism, not shown.
In the cylinder head 4, a combustion subchamber 10 formed having a substantially spherical shape is formed. A main combustion chamber 14 is formed between a top surface 5a of the piston 5 sliding in a cylinder 3a and a bottom surface 4a of the cylinder head 4. The combustion subchamber 10 communicates with the main combustion chamber 14 through a communication hole 12 that is inclined with respect to a sliding direction of the piston 5 indicated by an arrow. The combustion subchamber 10 includes an injector 20 that injects fuel into the combustion subchamber 10 and a glow plug 25 that heats an inside of the combustion subchamber 10.
A fuel passage pipe 30 that accumulates fuel and supplies fuel to the injector 20 is connected to the injector 20. Fuel is supplied to the fuel passage pipe 30 by the fuel supply system 40. The fuel supply system 40 includes a fuel pump 41, a fuel supply pipe 42, a pumping amount control valve 43, and a fuel tank 44. The fuel pump 41 is driven by a crank shaft 9 of the diesel engine 1 via a power transmission mechanism, not shown, and supplies fuel sucked from the fuel tank 44 by the fuel pump 41 to the fuel passage pipe 30 via the fuel supply pipe 42. A pumping amount control valve 43 is electrically operated, has a function of controlling the amount of fuel sucked by the fuel pump 41 to be released to the fuel tank side, and can adjust the fuel amount to be supplied from the fuel pump 41 to the fuel passage pipe 30.
Although not shown, the diesel engine 1 is a so-called multi-cylinder engine including a plurality of cylinders 3a, and the plurality of cylinders 3a are arranged in series with the cylinder block 3. The combustion subchamber 10 is formed correspondingly to each cylinder 3a, and the injector 20 and the glow plug 25 are provided for each of the combustion subchambers 10. Each injector 20 is connected to the common fuel passage pipe 30 and injects fuel into the combustion subchamber 10 with a fuel pressure accumulated in the fuel passage pipe 30. That is, the fuel pressure in the fuel passage pipe 30 becomes the injection pressure when the fuel is injected from the injector 20 into the combustion subchamber 10. The injector 20 is a so-called internally open valve type injector, an operation of which is electrically driven by an electromagnetic solenoid, not shown, and can inject fuel at arbitrary timing on the basis of an electric signal sent to the injector 20. The fuel passage pipe 30 is a tubular member extending in a direction perpendicular to the paper surface in
The intake system 50 introduces air (outside air) into the intake port 6 of the diesel engine 1. The intake system 50 includes an intake passage 52, and the intake passage 52 includes a compressor 72 of a supercharger 70 and an intake cooler (intercooler) 54. The intake passage 52 may include an intake control valve that adjusts the intake amount.
The exhaust system 60 exhausts the exhaust gas discharged from the diesel engine 1 to the outside of the diesel engine 1. An exhaust system 60 includes an exhaust passage 62. The exhaust passage 62 includes a turbine 74 of the supercharger 70. The exhaust passage 62 is connected to the exhaust port 8 of the diesel engine 1.
The EGR system 80 includes an EGR passage 81 that introduces a part of the exhaust gas flowing through the exhaust passage 62 as EGR gas into the intake port 6 of the diesel engine 1. An upstream end of the EGR passage 81 is connected to the exhaust passage 62. A downstream end of the EGR passage 81 is connected to an upstream side of the intake port 6 of the intake passage 52. The EGR passage 81 includes an EGR gas cooler 82 that cools the EGR gas. In the EGR passage 81, a cooler bypass passage 84 for bypassing the EGR gas cooler 82 and allowing the EGR gas to flow to the intake passage 52 side is provided. The cooler bypass passage 84 includes a bypass amount adjustment valve 86 that adjusts the amount of EGR gas to be bypassed. An EGR gas amount adjustment valve 88 is provided on the downstream side (intake passage 52 side) of the EGR gas cooler 82 in the EGR passage 81. By controlling an opening degree of the EGR gas amount adjustment valve 88, the amount of EGR gas introduced into the intake port 6 via the intake passage 52 can be adjusted.
The diesel engine 1 includes an engine ECU 100 as controller that controls the entire diesel engine 1. The engine ECU 100 is constituted by a computer and includes a central processing unit (CPU) that performs arithmetic processing in accordance with a control program, a read-only memory (ROM) that stores a control program and the like, a readable/writable random access memory (RAM) that temporarily stores detected detection values, arithmetic results and the like, an input interface, and an output interface (details are not shown).
The engine ECU 100 detects the operation state of the diesel engine 1, and in response to the detected operation state, it controls the injection timing, an injection pressure, an injection amount, a number of injections of the fuel supplied from the injector 20 to the combustion subchamber 10, an EGR gas amount introduced into the intake port and the like in accordance with a control program stored in advance in the ROM.
The engine operation state detector that detects the operation state of the diesel engine 1 described above will be described. As shown in
The operation of the engine ECU 100 will be described with reference to
Further, in parallel with the above-mentioned required main injection amount calculator 121, the engine rotation speed Ne and the required load L are input also to required main injection pressure calculator 122, and the injection pressure of the main injection required by the diesel engine 1 is output as the required main injection pressure Pm. When the required load L is low and when the engine rotation speed Ne is low, the required main injection pressure Pm is set to be reduced, and conversely, when the required load L is high and the engine rotation speed Ne is high, it is set to be high by a map or the like (not shown). When the required main injection pressure Pm is output, the required main injection pressure Pm is set as a target fuel pressure of the fuel passage pipe 30, and the pumping amount control valve 43 of the fuel pump 41 is controlled on the basis of a detection value of the fuel passage pipe pressure sensor 101 installed in the fuel passage pipe 30. As a result, the pressure in the fuel passage pipe 30 is always adjusted within a predetermined range in the vicinity of the required main injection pressure Pm.
After calculating the required main injection amount Qm and a required main injection pressure Pm, the required main injection amount Qm and the required main injection pressure Pm are then input to main injection number calculator 123, and a main injection number FNm for injection by dividing the main injection Fm into a predetermined number of times is calculated. A specific calculation flow of the main injection number calculator 123 will be described more specifically with reference to
As shown in
When the required main injection time FmT described above is acquired, the required main injection time FmT is input to spray tip reaching distance calculator 123b together with the required main injection pressure Pm, and a spray tip reaching distance FD of the spray injected from the injector 20 is calculated by referring to the map, not shown. The spray tip reaching distance FD is a value that increases as the required main injection pressure Pm is higher or as the required main injection time FmT is longer. Since the distance actually reached by the tip of the spray is affected by a nozzle diameter formed at the tip of the injector 20 and the shape of the nozzle, the map for acquiring the spray tip reaching distance FD is formulated by an experiment or the like for each injector 20.
When the spray tip reaching distance FD is calculated, it is input to main injection number calculator 123c, and the main injection number FNm is calculated. Here, when the main injection number FNm is calculated by the main injection number calculator 123c, a spray tip reaching distance limit value FDL is referred to. The spray tip reaching distance limit value FDL will be described with reference to
As shown in
By comparing the spray tip reaching distance limit value FDL set as described above with the spray tip reaching distance FD, if the spray tip reaching distance FD is smaller than the spray tip reaching distance limit value FDL, with one injection of the required main injection amount Qm, the fuel injected from the injector 20 does not reach the wall surface of the combustion subchamber 10 and thus, the main injection number FNm is set to one. Further, if the spray tip reaching distance FD is equal to or larger than the spray tip reaching distance limit value FDL, the spray F reaches the wall surface 10a of the combustion subchamber 10 when the main injection number FNm is injected once. Therefore, the main injection number FNm is set to a predetermined plurality of number of times so that the main injection Fm injected from the injector 20 becomes a multi-stage injection, and the required main injection amount Qm is divided in accordance with the number of divisions. The specific number of times to which the main injection number FNm is set can be determined by how much the spray tip reaching distance FD exceeds the spray tip reaching distance limit value FDL, but it may be confirmed by whether the tip of the spray F does not reach the wall surface of the combustion subchamber 10 by calculating injection time per injection with reference to the T-Q map on the basis of the fuel injection amount to be injected per injection, by calculating the spray tip reaching distance FD again each time it is increased to twice, three times and more, and by comparing it with the spray tip reaching distance limit value FDL. Further, even though the required main injection amount Qm is the maximum value that can be theoretically taken, if it is known that the tip of the spray F does not reach the wall surface of the combustion subchamber 10 by dividing it into two injections, when it is determined that the spray tip reaching distance FD is equal to or larger than the spray tip reaching distance limit value FDL, the main injection number FNm only needs to be set to 2. As described above, the main injection number calculator 123 outputs the predetermined number of times (main injection number FNm) when the main injection Fm is injected.
Returning to
When the main injection time Fmt per injection is calculated, it is input to total main injection time calculator 126 together with the previously calculated main injection number FNm per injection, and total main injection time FT from start of the main injection Fm to completion of all the main injections is calculated with reference to target injection interval FI. For example, the total main injection time FT when the main injection number FNm is 2 is calculated as follows.
Total main injection time FT=Main injection time Fmt per injection×2+Target injection interval FI
As a matter of course, when the main injection number FNm is 1, the target injection interval FI does not have to be considered, and the main injection time Fmt per injection becomes the total main injection time FT as it is. The target injection interval FI described above is determined by considering the minimum interval that should be opened in order to operate the injector 20 and to inject fuel in accordance with the T-Q map, but this is not limiting, and in addition to the interval that should be opened at the minimum, the interval may be increased or decreased depending on the operation condition.
As described above, when the total main injection time FT is calculated, it is input to main injection start timing calculator 127, and main injection start timing FS is calculated as injection start timing of the main injection Fm by referring to target main injection end timing FE. Procedures for calculating the main injection start timing FS will be described below.
Incidentally, as described above, the total main injection time FT is calculated on the basis of the time (μs). On the other hand, control of the fuel injection timing of the injector 20 is executed on the basis of the crank angle (CA) detected by the crank angle sensor 102. Therefore, when the main injection start timing FS is calculated, it is necessary to convert it into a crank angle and set it. With regard to the above, procedures for calculating the main injection start timing FS while converting it into a crank angle will be described with reference to
As the engine rotation speed Ne changes from low to high, an average speed of the piston 5 increases, and the time required for one cycle changes and decreases. On the other hand, as described above, the time required to inject all the required main injection amount Qm, that is, the total main injection time FT (μs) is not directly affected by the engine rotation speed Ne but depends on the required main injection pressure Pm and the required main injection amount Qm. Further, the fuel injection performed in the present embodiment is premised on performance of the preliminary injection Fp, the main injection Fm, and the ignition control injection Fc, and the main injection Fm needs to be completed at the target main injection end timing FE before the injection start timing of the ignition control injection Fc performed at the compression self-ignition timing in the vicinity of the compression top dead center only predetermined time T0. This predetermined time T0 is time set also by considering time during which the main injection Fm is sufficiently mixed with a vortex flow S of air (see
As described above, when the target main injection end timing Fe is set by the crank angle, the timing that goes back from the target main injection end timing FE only by the total main injection time FT is calculated as the main injection start timing FS so that the main injection Fm is completed at this target main injection end timing FE. As described above, since the total main injection time FT is also calculated by the time, the total main injection time FT is converted per crank angle (CA) similarly to the predetermined time T0 described above, and the total main injection period FTCA is calculated. After calculating the total main injection period FTCA, the timing that goes back from the target main injection end timing FE only by the above-mentioned total main injection period FTCA is calculated as the main injection start timing FS. By the above procedure, the main injection start timing FS is determined by the crank angle.
The target main injection end timing FE is set by the crank angle by the calculator of the above-mentioned main injection start timing FS, and the timing that goes back from the target main injection end timing FE only by the total main injection time FT is calculated as the main injection start timing FS so that the main injection Fm is completed at this target main injection end timing FE. Therefore, as the engine rotation speed Ne changes from low rotation to high rotation, the main injection start timing FS of the main injection Fm is advanced from the top dead center side to the bottom dead center side of the compression stroke.
When the diesel engine 1 is actually operated, the first time of injection of the main injection Fm1 of the divided main injection Fm is started at the above-mentioned main injection start timing FS. An injection period of the first main injection Fm 1 is a main injection period FmtCA per injection obtained by converting the main injection time Fmt per injection calculated by the above-mentioned main injection time per injection calculator 125 to a crank angle corresponding to the engine rotation speed Ne. Then, when the injection is performed only for the main injection period FmtCA per injection and is completed, an interval is opened only by the target injection interval FI until the injection of second main injection Fm2 is started. At this time, since the target injection interval FI is also set by time, a target injection interval FICA obtained by converting the target injection interval FI to a crank angle is calculated in accordance with the engine rotation speed Ne, and after the interval is opened only by the target injection interval FICA, the second main injection Fm2 is performed with a main injection period FmtCA per injection. The main injection Fm performed in this way is completed at the target main injection end timing FE, as shown in
As shown in
In the present embodiment, as shown in
In the present embodiment, the EGR system 80 that recirculates the exhaust gas from the exhaust system 80 to the intake system 50 is arranged, and the exhaust gas can be supplied to the intake passage 52 depending on the operation state. As a result, the emission of nitrogen oxides contained in the exhaust gas is reduced, and when premixture is formed by the preliminary injection Fp and the main injection Fm and the compression self-ignition is performed in the vicinity of the compression top dead center, the ignition timing can be favorably controlled by preventing premature ignition by throwing in the EGR gas and the like.
The subchamber diesel engine 1 of the present embodiment sets the injection pressure of the fuel injected from the injector 20 within the range of 8 MPa to 40 MPa, or more preferably within the range of 15 MPa to 25 MPa. With the subchamber diesel engine 1, desired combustion performance can be obtained even in the injection pressure range as above. That is, since the injection pressure can be set to be much lower than that of the recent direct injection diesel engine whose maximum injection pressure exceeds 200 MPa, it is not necessary to make the structure of the injector 20 itself excessively robust, and a system for injecting fuel can be simply configured by using the injector 20 that can be electrically driven from the fuel passage pipe 30, and a manufacturing cost can be kept low.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018-217400 | Nov 2018 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2019/041623 | 10/24/2019 | WO | 00 |
