Engine control device

Abstract

To suppress combustion fluctuation while reducing PNs and suppressing deterioration of fuel economy.SOLUTION: A control device 30 is applied to an engine 10 including a cylinder injection valve 13 for injecting CN fuel into a cylinder 11; and a piston 12 reciprocating in the cylinder 11. The control device 30 includes a CPU 31 that controls the cylinder injection valve 13. The CPU 31 derives an evaporation temperature that is a top face temperature of the piston 12 capable of attaining predetermined distillation characteristics of the CN fuel on the basis of evaporation characteristics of the CN fuel. When the top face temperature of the piston is an evaporation temperature or lower, the CPU 31 executes control of the cylinder injection valve 13 that enables reduction of unburned fuel in the cylinder 11 compared to when the top face temperature is higher than the evaporation temperature.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an engine control device that is applied to an engine equipped with a direct injection valve. [Background technology]

[0002] Patent Document 1 discloses an example of an engine control device that increases the number of split injections from a direct injection valve when the fuel property is heavy compared to when the fuel property is not heavy. Increasing the number of split injections in this way reduces piston wetting, and therefore the control device can reduce unburned fuel in the cylinder. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-291971 Summary of the Invention [Problem to be solved by the invention]

[0004] If the number of split injections from the cylinder injection valve increases, fuel economy may deteriorate and combustion fluctuations may occur. [Means for solving the problem]

[0005] An engine control device for solving the above problems is applied to an engine equipped with an in-cylinder injection valve that injects CN fuel into a cylinder and a piston that reciprocates in the cylinder, and includes a processing circuit that controls the in-cylinder injection valve. The processing circuit derives an evaporation temperature, which is the piston top surface temperature at which predetermined distillation characteristics of the CN fuel can be achieved, based on the evaporation characteristics of the CN fuel, and controls the in-cylinder injection valve when the piston top surface temperature is equal to or lower than the evaporation temperature, so as to reduce unburned fuel in the cylinder more than when the piston top surface temperature is higher than the evaporation temperature. [Effects of the Invention]

[0006] The engine control device has the effect of being able to reduce PN and suppress deterioration of fuel economy while suppressing combustion fluctuations. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a configuration diagram showing an outline of an engine control device according to an embodiment and an engine to which the engine control device is applied. [Figure 2] FIG. 2 is a block diagram showing each process executed by a processing circuit of the engine control device of FIG. [Figure 3] In FIG. 3, (A) to (D) are timing charts showing how the injection mode of the direct injection valve is changed. DETAILED DESCRIPTION OF THE INVENTION

[0008] An embodiment of an engine control device will be described below with reference to FIGS. 1 illustrates an engine 10 and a control device 30. The control device 30 corresponds to the "engine control device."

[0009] The engine 10 includes a piston 12 that reciprocates within a cylinder 11 and an in-cylinder injection valve 13 that injects CN fuel into the cylinder 11. "CN fuel" is a carbon-neutral fuel. In the cylinder 11, a mixture containing the CN fuel injected from the in-cylinder injection valve 13 and air introduced via an intake passage 15 is combusted by spark discharge from an ignition plug 14. Exhaust gas generated in the cylinder 11 is then discharged into an exhaust passage 16.

[0010] Detection signals from a plurality of sensors are input to the control device 30. The plurality of sensors include an air flow meter 21 and a fuel property sensor 22. The air flow meter 21 detects the intake air amount, which is the flow rate of air flowing through the intake passage 15. The fuel property sensor 22 detects the property of CN fuel.

[0011] The control device 30 includes a CPU 31 and a memory 32 that stores a control program executed by the CPU 31. The CPU 31 corresponds to a "processing circuit." By executing the control program in the memory 32, the CPU 31 controls fuel injection from the in-cylinder injection valve 13, the opening of the throttle valve 17, the ignition timing of the spark plug 14, and the like.

[0012] With reference to FIG. 2, various processes executed by the CPU 31 to control fuel injection from the direct injection valve 13 will be described. The CPU 31 executes an evaporation characteristic acquisition process M11, an evaporation temperature derivation process M13, a top surface temperature estimation process M15, and an injection mode determination process M17.

[0013] In the evaporation characteristic acquisition process M11, the CPU 31 acquires the evaporation characteristic of the CN fuel based on the detection signal of the fuel property sensor 22, for example.

[0014] In evaporation temperature derivation processing M13, the CPU 31 derives an evaporation temperature TPTh, which is the top surface temperature of the piston 12 that can achieve predetermined distillation characteristics of the CN fuel. An example of the predetermined distillation characteristic is T90. That is, the top surface temperature at which 90% of the fuel adhering to the top surface 12a of the piston 12 is estimated to evaporate is set as the evaporation temperature TPTh. For example, the CPU 31 refers to map MP1 to derive a temperature according to the evaporation characteristics of the CN fuel as the evaporation temperature TPTh.

[0015] In the piston top surface temperature estimation process M15, the CPU 31 derives an estimated piston top surface temperature TPt, which is an estimated value of the temperature of the piston top surface 12a of the piston 12. For example, the CPU 31 can derive the estimated piston top surface temperature TPt based on the temperatures of the coolant and oil circulating inside the engine 10.

[0016] In the injection mode determination process M17, the CPU 31 determines the injection mode of the in-cylinder injection valve 13 based on the evaporation temperature TPTh and the estimated top surface temperature TPt. Specifically, when the estimated top surface temperature TPt is equal to or lower than the evaporation temperature TPTh, the CPU 31 executes the unburned fuel reduction control as the injection mode. On the other hand, when the estimated top surface temperature TPt is higher than the evaporation temperature TPTh, the CPU 31 executes the normal control as the injection mode.

[0017] An example of normal control is injection control that sets the number of injections from one direct injection valve 13 in one combustion cycle to one. Unburned fuel reduction control is control that reduces adhesion of CN fuel to the top surface 12a of the piston 12 compared to when normal control is executed. If the amount of CN fuel adhesion to the top surface 12a can be reduced, the unburned fuel in the cylinder 11 can be reduced. An example of unburned fuel reduction control is control that increases the number of split injections compared to normal control. Of course, control of the direct injection valve 13 other than split injection may be adopted as unburned fuel reduction control as long as it can reduce adhesion of CN fuel to the top surface 12a. For example, retarding the injection timing can also reduce adhesion of CN fuel to the top surface 12a.

[0018] The operation and effect of this embodiment will be described with reference to Figures 3(A) to 3(D). In Figure 3(B), a first evaporation temperature TPTh1 is the evaporation temperature TPTh when CN fuel is the first fuel. On the other hand, a second evaporation temperature TPTh2 is the evaporation temperature TPTh when CN fuel is the second fuel.

[0019] Before timing t1, engine 10 is operating, and estimated top surface temperature TPt is higher than evaporation temperature TPTh. Therefore, normal injection is performed as the injection mode of direct injection valve 13. At timing t1, operation of engine 10 is stopped intermittently. As a result, estimated top surface temperature TPt drops.

[0020] At a subsequent timing t2, the operation of the engine 10 is restarted. At the timing t2, the estimated top surface temperature TPt is equal to or lower than the evaporation temperature TPTh, so split injection is selected as the injection mode of the direct injection valve 13. Therefore, split injection is performed as the unburned fuel reduction control. This reduces the adhesion of CN fuel to the top surface 12a of the piston 12.

[0021] When the air-fuel mixture begins to burn in the cylinder 11, the temperature of the top surface 12a of the piston 12 rises. When CN fuel is the first fuel, the estimated top surface temperature TPt becomes higher than the evaporation temperature TPTh (i.e., the first evaporation temperature TPTh1) at timing t3. Therefore, the injection mode is changed from split injection to normal injection. This suppresses an increase in PN emissions, which are the amount of PN contained in the exhaust, and also suppresses a deterioration in fuel economy, compared to when split injection is continued. Furthermore, combustion fluctuations are suppressed.

[0022] If the second fuel is CN fuel, the estimated top surface temperature TPt becomes higher than the evaporation temperature TPTh (i.e., the second evaporation temperature TPTh2) at timing t4, and therefore the injection mode is changed from split injection to normal injection at timing t4.

[0023] 3 also shows a comparative example in which normal injection is selected as the injection mode when the engine 10 is restarted, regardless of whether the estimated top surface temperature TPt is equal to or lower than the evaporation temperature TPth. In FIGS. 3(C) and 3(D), the transition in this comparative example is shown by the two-dot chain line. [Explanation of symbols]

[0024] 10...engine, 11...cylinder, 12...piston, 13...direct injection valve, 30...control device, 31...CPU, 32...memory

Claims

[Claim 1] The invention is applied to an engine equipped with an in-cylinder injection valve that injects CN fuel into a cylinder and a piston that reciprocates within the cylinder, a processing circuit for controlling the in-cylinder injection valve; The processing circuitry deriving an evaporation temperature, which is the temperature of the top surface of the piston, that can realize predetermined distillation characteristics of the CN fuel based on the evaporation characteristics of the CN fuel; When the temperature of the top surface of the piston is equal to or lower than the evaporation temperature, the control of the in-cylinder injection valve is performed so as to reduce unburned fuel in the cylinder more than when the temperature of the top surface of the piston is higher than the evaporation temperature. Engine control device.

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