JPH03175155A - Combustion controller for alcohol diesel engine - Google Patents

Abstract

PURPOSE:To display the effect of the improvement of fuel cost and engine output, by controlling a temperature regulation means so that the temperature of glow plugs may be lowered at an engine more than middle load operation, in accordance with a catalytic temperature and pressure within a combustion chamber. CONSTITUTION:At the operation sphere of an engine 1 more than middle load opera tion, pressure P within a combustion chamber 6 is detected by means of a pressure sensor 9, and the combustion change of mixed air caused by the lowering control of the temperature of glow plugs 8... is detected by means of the catalytic temperature Tc of a catalyst device 14, as the pressure P is being restrained so that it may become at the range of pressure which is less than allowable pressure, and the temperature of glow plugs 8... is conducted with lowering control as much as possible so that the temperature Tc may be contained to a temperature which is less than an allowable one. As a result, a mixed air ignition lag time becomes as much longer, and a situation in which the spray of fuel injected from a combustion injection valve 7 is uniformly distributed within the combustion chamber 6, is realized, and pre-mixed combustion is increased, so the rate of air utilization at the time of the combustion of mixed air becomes larger, and torque generated at the engine 1 becomes larger, and at the same time the cost of fuel is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to improvements in combustion control devices for alcohol diesel engines that use low cetane fuels such as methanol.

(Prior Art) Conventionally, as a type of diesel engine, one that uses alcohol such as low cetane fuel as a fuel is known, for example, as disclosed in Japanese Utility Model Application Publication No. 62-56743.

Incidentally, alcohol such as low cetane fuel has a characteristic that its flammability range is narrower than that of gasoline. Therefore, in order to improve the combustibility, for example,
Utilizing the technology disclosed in Publication No. 79022, a glow plug is placed inside the combustion chamber of a direct injection engine, and by heating this glow plug to a high temperature, a mixture containing low cetane fuel is forcibly ignited. It is conceivable to increase the combustibility by

(Problem to be solved by the invention) In that case, the temperature of the glow plug is not always maintained at a high temperature,
The inventors have learned that in the region of medium load or higher, controlling the temperature lower than in low load can improve fuel efficiency and improve engine output.

In other words, if the temperature of the glow plug is lowered than during low-load operation when the engine is operating under medium load or higher, the ignition delay time of the mixture containing low-cetane fuel will increase, and this will increase the proportion of the mixture that undergoes premixed combustion. This increases the air utilization rate during combustion, making it possible to improve fuel efficiency and engine output.

However, if the temperature of the glow plug is lowered too much,
As shown in FIG. 5, the pressure within the combustion chamber increases, and the combustion fluctuations of the air-fuel mixture become severe.If these fluctuations become too large, the pressure within the combustion chamber decreases, resulting in a problem of misfire. Moreover, as the combustion fluctuations of the air-fuel mixture increase, the amount of carbonized nitrogen HC increases, leading to a decrease in emissions.

The present invention has been made in view of the above, and an object of the present invention is to reduce the pressure in the combustion chamber by appropriately controlling the temperature of the glow plug when the temperature of the glow plug is lowered at engine loads or higher. Maximizes the effects of improving fuel efficiency and engine output by controlling the glow plug temperature to decrease at medium loads and above, while minimizing the above drawbacks by keeping the rise and combustion fluctuations of the mixture within an allowable range. The goal is to make the most of it.

(Means for Solving the Problems) In order to achieve the above object, in the present invention, the temperature of the glow plug is controlled according to the pressure inside the combustion chamber, and when the combustion fluctuation of the air-fuel mixture increases, the amount of hydrocarbon HC increases. Considering that the temperature of the catalyst in the catalyst device placed in the exhaust passage of the engine increases due to the temperature of the catalyst, the combustion fluctuation of the air-fuel mixture is detected based on this catalyst temperature, and the temperature of the glow plug is controlled to decrease depending on the catalyst temperature. We will do so.

In other words, the specific solution of the present invention is based on an alcohol diesel engine that uses low cetane fuel such as methanol as fuel. A glow plug facing the combustion chamber and forcibly igniting the fuel supplied to the combustion chamber, and a temperature adjustment means for adjusting the temperature of the glow plug are provided. Pressure detection means detects the pressure within the combustion chamber; catalyst temperature detection means detects the temperature of the catalyst device disposed in the exhaust passage of the engine; A control means is provided for controlling the temperature adjusting means so as to reduce the temperature of the glow plug in accordance with the catalyst temperature at a medium load or higher of the engine.

(Function) With the above configuration, in the present invention, when the engine load is medium or above, the temperature of the glow plug is controlled to decrease according to the pressure in the combustion chamber and the catalyst temperature, so when the pressure in the combustion chamber approaches the allowable limit. , the glow plug temperature reduction control is also stopped, the temperature of the glow plug is maintained at the temperature at that point, and the pressure does not rise above the allowable limit. In addition, the combustion fluctuation of the air-fuel mixture increases due to the control to lower the glow plug temperature.
When the amount of hydrocarbon HC increases and the temperature of the catalyst device rises and approaches the permissible limit, control for lowering the glow plug temperature can be stopped, so that combustion fluctuations in the air-fuel mixture do not exceed the permissible range. As a result, fuel efficiency is improved by increasing premix combustion by controlling the temperature of the glow plug to decrease.
And the effect of improving the engine output can be significantly obtained.

(Effects of the Invention) As explained above, according to the combustion control device for an alcohol diesel engine of the present invention, the temperature of the glow plug, which is arranged in the combustion chamber and heated to a high temperature, is reduced in the region of engine medium load or above. This reduction can be properly controlled by controlling the pressure inside the combustion chamber and the temperature of the catalyst device, thereby improving fuel efficiency and improving engine efficiency while suppressing an excessive rise in the pressure in the combustion chamber and an increase in the amount of hydrocarbons generated. It is possible to effectively improve the output.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, reference numeral 1 denotes a four-cylinder diesel engine that uses low cetane fuel such as methanol, and four cylinders 2a to 2d arranged in a row are formed in the longitudinal direction of the engine. Each of the cylinders 2a to 2d has a recess 4a formed in the upper part of the piston 4 fitted into the cylinder 3, and a cylinder located above the recess 4a, as shown in FIG. 2 for the first cylinder 2a. A combustion chamber 6 is formed by the head 5 .

In FIG. 2, a fuel injection valve 7 inserted from above the cylinder head 5 faces the center of the combustion chamber 6, and a fuel injection valve 7 inserted from above the cylinder head 5 faces the combustion chamber 6. room 6
A glow plug 8 that is heated to a high temperature in order to forcibly ignite the fuel supplied therein is disposed, and its tip faces into the combustion chamber 6. Also, the first cylinder 2. In the combustion chamber 6 of a, a piezoelectric pressure sensor 9 as a pressure detection means for detecting the pressure inside the combustion chamber 6 is arranged on the opposite side of the glow plug 8 of the fuel injection valve 7 in FIG. ing.

In the above FIG.
An intake passage 12 has an opening communicating with the combustion chamber 6 of d, and one end thereof is 4.
An exhaust passage that branches out and communicates with the combustion chambers 6 of each cylinder 2a to 2d, and the other end of which gathers and is open to the atmosphere. A catalyst device 14 for purification and a silencer 15 are arranged downstream thereof.

In addition, in FIG. 1, reference numeral 18 indicates the fuel injection valve 7 of each cylinder.
This is an injection pump control device that includes a fuel controller 19 that adjusts the fuel injection amount and injection timing from ..., an electronic governor 17, and the like. Furthermore, in Figure 1, 20
is a plug temperature control device serving as a temperature adjustment means for adjusting the temperature of the glow plugs 8 of each cylinder. In the plug temperature control device 20, the glow plugs 8 are connected in parallel with each other, and are connected to the vehicle battery 23 via the normally open contact 22a of the rapid heating relay 22 provided in the common wiring 21. .

Further, a control power transistor 25 is connected in parallel to the normally open contact 22a of the rapid heating relay 22, and a power supply circuit for the glow plug 8 of a predetermined cylinder is connected to a power supply circuit for measuring the amount of current supplied to the glow plug 8. A standard resistor 26 is provided.

The rapid heating relay 22 and the control power transistor 25 are operated and controlled by a plug controller 28 that includes a CPU, etc., and the controller 28 includes the following:
A voltage signal generated across the standard resistor 26 is input. As shown in FIG. 3, the controller 28 turns on the rapid heating relay 22 at the start of temperature control of the glow plugs 8, and contacts 22a of the relay 22.
is closed and the glow plug 8 is energized to rapidly heat it and raise its temperature rapidly, and then the contact 22a is opened and the amount of current is monitored by the voltage signal across the standard resistor 26. The control power transistor 25 is duty controlled to set the temperature of the glow plug 8 to the target temperature To.
It has a heating function.

Furthermore, 30 is a main controller having a CPU etc. inside, and the controller 30 includes a rotation speed sensor 31 that detects the rotation speed of the engine 1, a water temperature sensor 32 that detects the cooling water temperature of the engine 1, Fuel injection valve 7・
The injection timing sensor 33 detects the injection timing of fuel from ..., the accelerator opening sensor 34 detects the amount of depression of the accelerator pedal 40, the pressure sensor 9 shown in FIG. 2 above, and the temperature of the catalyst device 14 are detected. Detection signals from a catalyst temperature sensor 35 serving as catalyst temperature detection means are input.

Then, the main controller 30 outputs a fuel injection ff1Q signal and its injection timing T Inj signal to the fuel controller 19, and also outputs a signal multiplied by the target temperature Tg of the glow plugs 8 to the plug controller 28. Functions to output.

Next, glow plug 8 at medium load or above of engine 1...
The temperature control will be explained based on the control flow shown in FIG.

After starting, the engine rotation speed is read from the rotation speed sensor 31 in step S1, and the accelerator pedal opening from the accelerator opening sensor 34 is read in step S2, and then the engine rotation speed and the accelerator pedal are read in step S3. The target glow plug temperature Tg is read and set from a glow plug temperature map preset according to the opening degree, and the target injection amount is determined from the fuel injection amount map and injection timing map preset according to the engine speed and the accelerator pedal opening degree. and the injection timing T 1nj are read and set.

After that, in step S4, the catalyst temperature TC of the catalyst device 14 from the catalyst temperature sensor 35 is read, and the catalyst temperature Tc is compared with the allowable maximum temperature Tcmax, and Tc<Tcmax.
When the temperature is low, good combustion of the air-fuel mixture is occurring and there are few combustion fluctuations, so in step S5, fuel is injected in an amount exceeding the target fuel injection amount, and the process returns to step S1.

On the other hand, when the catalyst temperature Tc is high, reaching Tc - Tcmax in step S4, the temperature of the glow plugs 8 is set to a temperature (Tg - ΔTg) lower than the target temperature Tg by a minute temperature ΔTg in step S6. Control. As a result, premix combustion increases, and the combustion fluctuation of the mixture becomes fifth.
Although it increases as shown in the figure, the air utilization rate during combustion increases and the catalyst temperature Tc decreases. In this case, as the combustion fluctuation increases, the pressure within the combustion chamber 6 increases as shown in the figure.

Then, in step S7, the pressure P in the combustion chamber 6 is read and compared with the allowable maximum pressure P IjaX, and in step S8, the catalyst temperature Tc is compared with the allowable temperature T cmax,
If P < P ilaw and Tc < rca+ax, the process returns to step S6 and the glow plugs 8...
・Continue controlling temperature reduction.

On the other hand, when the pressure in the combustion chamber 6 first reaches P - P max in step S7, the temperature reduction control of the glow plugs 8 is stopped in step S9, and the temperature is fixed at that time. At the same time, the fuel injection amount is fixed at the current injection amount in step SIO, and the process returns to step S1. On the other hand, when the catalyst temperature Tc reaches Tc-Tcmax first, in order to lower the catalyst temperature Tc of the step S++ lever, the fuel injection timing is advanced by a minute value ΔTlnj (Tinj-ΔTlnj ), the combustion fluctuation of the air-fuel mixture is reduced and the catalyst temperature Tc is lowered. After that, in step S+2, the catalyst temperature Tc is read again and compared with the allowable value 'rcwax, and if the low temperature state is Tc<Tcraax, the process returns to step S6 to control the temperature reduction of the glow plugs 8... However, if it is still Tc - Tcmax, the process returns to step S9 and the temperature of the glow plugs 8 . . . is fixed at the temperature at that time.

Therefore, according to the control flow shown in FIG. 4 above, the pressure sensor 9
and the output of the catalyst temperature sensor 35, P < P max according to the pressure P in the combustion chamber 6 and the catalyst temperature Tc.
and within the range of Tc<Tcmax, the glow plug 8...
A control means 40 for controlling the plug temperature adjusting device 20 so as to reduce the temperature Tg of the engine 1 at a medium load or above.
It consists of

Therefore, in the above embodiment, in the operating range of the engine 1 at medium load or higher, the inside of the combustion chamber 6.

The pressure P is detected by the pressure sensor 9, and this pressure
As shown in the figure, the combustion fluctuation of the air-fuel mixture caused by the temperature reduction control of the glow plugs 8 is detected by the catalyst temperature Tc of the catalyst device 14 while suppressing the pressure to a range below the allowable pressure Pfflax, The glow plug 8...
・The temperature is controlled to be as low as possible.

As a result, the ignition delay time of the air-fuel mixture becomes longer, and the fuel spray injected from the combustion injection valve 7 becomes uniformly distributed within the combustion chamber 6, increasing premixed combustion. As a result, as shown in Fig. 7, the air utilization rate during the combustion of air increases, and as shown in Fig. 7, the torque generated by the engine 1 becomes greater than that of an engine that does not control the decrease in glow plug temperature as in the past, and the fuel consumption also decreases. is improved in all areas above medium engine load.

Moreover, since the catalyst temperature TQ is suppressed to less than the allowable temperature TcIMax, deterioration and damage to the catalyst device 14 can be effectively prevented.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention, in which Fig. 1 is an overall configuration diagram, Fig. 2 is a vertical cross-sectional view of the first cylinder, Fig. 3 is an explanatory diagram of temperature control of the glow plug, and Fig. 4 is an illustration of the temperature control by the main controller. A flowchart showing control of fuel injection amount and glow plug temperature, FIG. 5 shows catalyst temperature with respect to glow plug temperature,
6 and 7 are diagrams showing the combustion fluctuation of the air-fuel mixture and the change characteristics of the combustion chamber pressure, and are diagrams showing the effects of the present invention. 1...Diesel engine, 6...Combustion chamber, 8...
・Glow plug, 9...pressure sensor (pressure detection means)
, 14... Catalyst device, 20... Plug temperature detection device/temperature adjustment means>, 28... Plug controller,
30... Main controller, 35... Catalyst temperature sensor (catalyst temperature detection means), 40... Control means.

Claims (1)

[Claims] (1) In an alcohol diesel engine that uses low cetane fuel such as methanol as fuel, there is a glow plug that faces the combustion chamber and forcibly ignites the fuel supplied to the combustion chamber, and a temperature controller that adjusts the temperature of the glow plug. pressure detection means for detecting the pressure in the combustion chamber; catalyst temperature detection means for detecting the temperature of the catalyst device disposed in the exhaust passage of the engine; A combustion control device for an alcohol diesel engine, comprising: control means for controlling the temperature adjustment means so as to reduce the temperature of the glow plug at intermediate engine loads or higher according to indoor pressure and catalyst temperature.