JPH01267366A - Glow plug control device for diesel engine - Google Patents

Abstract

PURPOSE:To always ensure a given glow plug temperature and to improve ignitability, by a method wherein a glow temperature is controlled in a stepped manner so that, in a low load region, the temperature of a glow plug is increased to a given high value and in a high load region, the temperature of the glow plug is decreased to a given low value. CONSTITUTION:First - fourth glow plugs 11 (11a-11d) mounted to cylinders A-D, respectively, are energized through common lead wire 16 and branch lead wires 17a-17d, and a heat generating amount thereof is controlled through a power transistor Tr23. The transistor Tr23 is controlled by a control box 22 according to a detecting result of a current flowing through a fixed resistor 30 located in the fourth branch lead wire 17d and a glow plug set temperature computed according to an engine load in a main controller 29. Namely, the transistor Tr23 is controlled in a way that a glow plug temperature is controlled in a stepped manner so that, in a low load region, the temperature of a glow plug 11 is increased to a given value and in a high load region, it is reduced to a given value.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a glow plug control device for a diesel engine, and particularly for controlling the glow plug temperature of a glow assist diesel engine using low cetane fuel such as methanol. related to things.

(Prior art) In a diesel engine, fuel is normally ignited and combusted due to the temperature rise associated with adiabatic compression of the intake air, so when the engine temperature is low, such as when starting the engine or when it is cold, the compression There was a problem in that the temperature of the intake air sometimes did not rise sufficiently, resulting in poor ignition performance. Therefore, a glow plug equipped with a heating element having a predetermined electrical resistance is installed in the combustion chamber, and in a predetermined operating range, the glow plug's heating element is energized, and the heat generated assists the ignition of the fuel. Glow-assist diesel engines have been proposed (for example, Utility Model Application No. 57-44932
(see publication).

In a normal glow-assist diesel engine that uses light oil as fuel, for example, as shown in Figure 12, after the ignition switch is turned on, the glow plug is rapidly preheated, and the globe lug temperature reaches a predetermined value T+℃. Start cranking after t5 seconds, keep the glow plug temperature at 11℃ until the engine fully explodes, and stepwise lower the glow plug temperature to Tt'C after t8 seconds after the engine fully explodes. The glow plug temperature is maintained at T't'C until 5 seconds after the warm-up is completed, and after the warm-up is completed, the energization to the glow plug is stopped and the glow assist is completed.

(Problems to be Solved by the Invention) In recent years, carbon dioxide has been shown to have good emission performance, particularly because it reduces the amount of carbon generated, and it can be produced from coal, natural gas, etc., which is advantageous in terms of resources. ,
Using alcohol such as methanol as fuel 1. Diesel engines have been proposed that use diesel fuel or light oil mixed with alcohol as fuel.

Diesel engines that use methanol as fuel have also been proposed to have glow plugs installed to improve ignition performance, but these engines are also equipped with glow plugs that use ordinary glow plugs that use light oil as fuel. At present, glow plug control as shown in FIG. 12 is performed, similar to assist diesel engines.

However, the combustion characteristics of light oil and alcohols such as methanol are clearly different, and the glow plug control described above, which is considered appropriate for light oil, is not effective in improving ignition performance, durability of glow plugs, or efficiency in power consumption. From the point of view,
It is questionable whether it is also suitable for diesel engines that use low-cetane fuels such as methanol, but this point has not been studied in the past. There is a need for the development of a glow plug control device.

(Means for Solving the Problem) Therefore, the inventor of the present application has determined the glow plug temperature required to maintain good ignition performance (hereinafter referred to as glow plug required temperature) for a glow-assist diesel engine that uses methanol, etc. as fuel. The required glow plug temperature depends on the engine load. For example, as shown in FIG. 13, the required glow plug temperature depends on the engine load. For example, as shown in FIG.
In the operating range below +, Td becomes constant at 'C,
The results show that the engine load rapidly decreases to Td*'C near the engine load Pdi in a stepwise manner, and then gradually decreases as the load increases in the higher load range.

The present invention focuses on the above facts, and provides a diesel engine equipped with a glow plug that assists in ignition of fuel. ,
In a low load region where the engine load detected by the load detection means is below a predetermined value, the glow plug becomes a predetermined high temperature, while in a high load region where the engine load exceeds the predetermined value, the glow plug becomes a predetermined low temperature. Provided is a glow plug control device for a diesel engine, characterized in that it is provided with a glow plug temperature control means for controlling the glow plug temperature in steps. The glow plug temperature is changed stepwise with respect to the engine load so that it becomes high temperature in a predetermined low load range and low temperature in a high load range, and the glow plug temperature is adjusted to the actual glow plug temperature as shown in Fig. 13. Since the glow plug temperature is almost the same as the required glow plug temperature, the glow plug temperature necessary for igniting the fuel is ensured.
Improves ignition performance. In addition, since the glow plug temperature is kept at a minimum, excessive current is not supplied to the glow plug, reducing the power consumption of the glow plug and improving the net thermal efficiency of the engine. The durability of the glow plug can be improved.

(Example) Examples of the present invention will be specifically described below.

As shown in Fig. 1, a common intake passage 1 is provided to supply intake air to a four-cylinder diesel engine DE that uses methanol as fuel. an air cleaner 2 that removes air intake air, an intake temperature sensor 3 that detects intake air temperature, an intake throttle valve 6 that is opened and closed by an actuator 5 via a link mechanism 4, and a throttle valve opening sensor that detects the opening degree of the intake throttle valve 6. A degree sensor 7 is provided. The common intake passage 1 has a throttle valve 6
At the downstream branch part 8, the first to fourth cylinders A and B.

It branches into first to fourth vertical intake passages 98 to 9d, which supply intake air to C and D, respectively. Although methanol is used as the fuel in this example, the present invention is not limited to this, and may be applied to diesel engines that use other alcohols as fuel or light oil mixed with alcohol, and even diesel engines that use light oil mixed with alcohol as fuel. This can also be applied to diesel engines, etc., which are operated at low compression ratios using light oil as fuel.

The first to fourth cylinders A to D are provided with first to fourth glow plugs Ila to Il for assisting in ignition of fuel, respectively.
d is provided. These first to fourth glow plugs Ila to lid are ordinary glow plugs equipped with a heating element having a predetermined electrical resistance, and when the heating element is energized, it generates heat depending on the magnitude of the current, This heat generation assists in igniting the fuel. Note that the electrical resistance of the heating element changes with a predetermined characteristic depending on its temperature, so as explained later, the temperature of the heating element can be calculated by measuring the electrical resistance of the heating element. It has become.

A common conducting wire 16 is connected to the first to fourth glow plugs IIa=IId from the positive terminal of the battery 15, and a common conducting wire 16 is connected to the first to fourth glow plugs IIa and IId, respectively.
The first to fourth branch conductors 17a to 17a connected to a to Ild
Current is supplied through 7d. In addition, the negative terminal of the battery 15 is grounded! 8 is connected. An electromagnetic switch 21 is interposed in the common conductor 16, and the electromagnetic switch 2 is closed when energized from a control box 22, which will be explained in detail later. When it is cut off, it is opened and the common conduction 16 is cut off.

Further, in order to control the voltage (current) applied to the first to fourth glow plugs jla=lId, that is, the amount of heat generated, an spnp type power transistor 23 is provided, and the base 23b of the power transistor 23 is connected to the base side conductor 24. The emitter 23e is connected to the common conductor 16 from the electromagnetic switch 21 to the battery 15 side via the emitter side conductor 25, and the collector 23c is connected to the first to fourth branch conductors 17a=1.
7d. When the voltage applied to the base 23b (base voltage) is lower than the voltage applied to the emitter 23e (emitter voltage), the power transistor 23 allows current to flow from the emitter 23e to the collector 23c in accordance with the base voltage. When the voltage is higher than the emitter voltage, no current flows from the emitter 23e to the collector 23c. Therefore, by adjusting the base voltage, the first to fourth
The amount of electricity supplied to the glow plugs Ila to Ild, that is, the amount of heat generated, can be controlled.

The control tool box 22 is configured such that the temperatures of the first to fourth glow plugs Ila to lid follow the glow plug setting temperature applied from the main controller 29.
It is a control device that controls the amount of electricity supplied to the first to fourth glow plugs 11a to Ild, and together with the main controller 29, constitutes glow plug temperature control means described in the claims of the present application. And control box 2
2 detects the voltage applied to the fixed resistor 30 interposed in the fourth branch conductor 17d, and calculates the current value flowing through the fourth branch conductor 17d from this voltage value and the resistance value (known) of the fixed resistor 30. Then, calculate the electrical resistance of the fourth glow plug Ild from this current value and the voltage at point Y downstream of the fixed resistor 30, that is, the voltage applied to the fourth glow plug Ild,
The temperature of the fourth glow plug lld is calculated from this electrical resistance value. Note that the functional relationship between the temperature of the glow plug and the electrical resistance value is stored in the control box 22.

The main controller 29 controls the intake temperature detected by the intake temperature sensor 3, the throttle valve opening detected by the throttle valve opening sensor 7, and the rotation speed sensor 3! The engine speed detected by the engine speed, the crank angle detected by the crank angle sensor 32, the water temperature detected by the water temperature sensor 33, the oil temperature detected by the oil temperature sensor 34, and the fuel pump (F I P) 35. The load, deceleration, etc. detected by the provided load sensor 36 are used as input information to control the opening and closing of the throttle valve 6 and apply the glow plug set temperature to the control box 22.

The operation of the above configuration will be explained below. When the engine DE is started, the coil of the electromagnetic switch 21 is energized by the control box 22, the electromagnetic switch 21 is closed, and the first ~The maximum current is passed through the fourth glow plugs lla~lid, respectively,
heats up rapidly. As described above, the temperature of the fourth glow plug lld is constantly detected by the control box 22 by measuring the voltage across the fixed resistor 30. Moreover, the first to third glow plugs 11a=ll
Since the temperature of c is considered to be almost the same as the temperature of the fourth glow plug Ild, the temperature of the fourth glow plug Ild is taken as a common glow plug temperature.

Then, the glow plug temperature changes to the main controller 29.
When the predetermined set temperature Tgo°C applied to the control box 22 is reached, the electromagnetic switch W21 is opened, and a base voltage is started to be applied to the base 23b of the power transistor 23, and control of the glow plug temperature is started. Ru. Then, cranking is started and engine D
The base voltage of the power transistor 23 is feedback-controlled by the control box 22 using the glow plug temperature as input information so that the glow plug temperature remains constant at Tgo° C. until E is completely detonated. The control mode during this time is similar to the control mode (0 to t3 seconds) of a glow-assist diesel engine that uses light oil as fuel, as shown in Fig. 12, but the glow plug set temperature during cranking is different. .

After the complete explosion of the engine DE, the glow plug set temperature corresponding to the engine load is applied from the main controller 29 to the control box 22, as shown by the polygonal line F in FIG. so that it follows the glow plug setting temperature above.
The base voltage of the power transistor 23 is feedback-controlled. The glow plug set temperature indicated by the above bend @F is constant at T g + 'C in the region below the engine load or a predetermined value P1 (hereinafter referred to as switching load), and changes stepwise with switching load Pl, In the region exceeding the switching load P1, T gt'c is constant. The characteristics of the glow plug setting temperature with respect to the engine load are as follows:
It has a characteristic that almost matches the required glow plug temperature (see FIG. 13), as shown by the polygonal line F, which was determined by actual measurements. In addition, in the conventional type, the glow plug set temperature has a characteristic of being constant at Tg+'C regardless of the magnitude of the load, as shown by the straight line F3. Therefore, according to the glow plug temperature control according to the present invention, the glow plug temperature almost matches the required glow plug temperature, so ignition performance can be maintained well, and furthermore, the glow plug temperature can be prevented from becoming unnecessarily high. Since this can be prevented, the durability of the glow plug can be improved, and since power consumption is kept to the minimum necessary, fuel efficiency can be improved. In this case, the power consumption of the glow plug, as shown by the polygonal line F4 in FIG. %, maximum load P max 4
A 5% reduction in power consumption is achieved.

By the way, according to the experimental results, the switching load P is not fixed but changes depending on the operating condition of the engine. Therefore, in this embodiment, the switching load P is corrected according to various operating conditions. However, a method of correcting such switching load P will be described below.

First, the switching load P+ is corrected based on the engine speed. In other words, at high rotation, the engine D
Since E becomes high temperature and ignition performance improves, switching load P
, is moved to the low load side, and the glow plug temperature is switched to the low temperature side (Tgt° C.) from the lower load range to prevent the glow plug temperature from increasing unnecessarily. Conversely, at low engine speeds, the temperature of the engine DE decreases and the ignition performance decreases, so the switching load P1 is moved to the high load side and the glow plug temperature is increased to a high tFjL (T g
+°C) to maintain good ignitability.

Specifically, as shown in FIG. 4, for example, the characteristics of the glow plug set temperature with respect to the engine load are set as shown by the polygonal line G at high speeds, and as shown by the polygonal line G at normal times (the polygonal line G,).
Move the switching load to the lower load side, and set it as shown by the polygonal line G when the paper is rotating, and during normal operation (the polygonal line GI)
The switching load is moved to the higher load side. As shown in FIG. 5, the switching load P has a characteristic that it decreases linearly as the engine speed increases.

Furthermore, the switching load P is corrected based on the intake air temperature. That is, when the intake air temperature is high, the intake air becomes sufficiently high in temperature due to compression and the ignitability improves, so the switching load P is moved to the lower load side, and vice versa when the eye air temperature is low. In this embodiment, the switching load P
When the intake temperature is low, the characteristics of , with respect to the engine speed are shifted to the higher load side than in normal times (straight line CS), as shown by straight line G in FIG. That is, the glow plug temperature is increased to a higher load range to compensate for the decrease in ignition performance due to the low intake air temperature. On the other hand, when the intake air temperature is high, the glow plug is moved to the low load side, as shown by straight line G, to prevent the glow plug temperature from increasing unnecessarily.

Further, the switching load P1 is corrected according to the warm-up state of the engine DE. In other words, before the warm-up of the engine DE is completed, the intake air temperature does not rise sufficiently during compression and the ignition performance deteriorates. As shown by straight line G8, the load is moved to a higher load side than after completion of warm-up (straight line G8) to compensate for the decrease in ignition performance.

By controlling the glow plug temperature as described above, basically the ignitability is improved and the power consumption is reduced, but if the engine load changes from the high load side to the low load side beyond the switching load P1. and the glow plug set temperature is T g*
When changing from 'c to T g +°C, the ignition performance slightly deteriorates due to a transient phenomenon caused by the glow plug having a heat capacity, so this example is intended to improve this. This will be explained.

As shown in Fig. 8, at a certain time (t), the accelerator opening changes from the open side to the closed side, as shown by the polygonal line, and the engine load accordingly changes, as shown by the polygonal line 4. As shown, the switching load P changes from the high load side to the low load side,
When the glow plug setting temperature is below T g
It increases stepwise from t'c to T g + °C,
1st to 4th glow plugs! Since a to Ild have a predetermined heat capacity, the actual glow plug temperature does not rise stepwise, but gradually reaches TL° C. with a considerable time delay, as shown by the curve. During this time, the actual glow plug temperature has not reached the required glow plug temperature indicated by K1, so the ignition performance deteriorates. In order to prevent this, in this embodiment, the engine load changes from the high load side to the low load side and becomes less than the switching load P1, and the glow plug set temperature increases stepwise from T g * 'C to 181 °C. In this case, as shown by 3 on the polygonal line, the opening degree of the calibration valve 6 is reduced by ΔX% for a predetermined time Δt to reduce the intake air amount, and the first to fourth glow plugs IIa=1
By reducing the amount of heat dissipated by 1d, the glow plug temperature will quickly decrease to T.
The temperature is set to rise from gt°C to 181°C.

In this case, the lower the switching load P1 is, the larger the excess air ratio is, making it difficult for the glow plug temperature to rise. To correct this, as shown in FIG. The valve opening degree (throttling amount) is increased to reduce the amount of intake air, thereby speeding up the rise in glow plug temperature.

Also, when the engine speed is high, the engine DE is at a high temperature, and the temperature of the glow plug increases quickly, so as shown in Figure 10, the higher the engine speed, the longer the throttle valve closes. I keep it short.

In addition, the glow plug setting temperature is T g t 'C to 7
Even if the calibration valve 6 is closed for a predetermined period of time as described above to speed up the rise in glow plug temperature when the temperature is changed to g+℃, the intake air amount will suddenly increase when the throttle valve 6 is fully opened again. This may cause the glow plug temperature to drop temporarily. Therefore, this embodiment is designed to prevent this. That is, as shown by the line L5 in FIG. 11, when the throttle valve 6 is fully opened again (see 8), the glow plug temperature temporarily decreases as shown by the line 4 due to a sudden increase in the amount of intake air. descend. In order to prevent this, while the throttle valve 6 is closed, the glow plug set temperature is set to Tg3°C (broken line L1), which is higher than the original glow plug set temperature Tg+°C (broken line) by a predetermined value. The temperature of the glow plug is prevented from decreasing when the throttle valve 6 is fully opened. As a result, the glow plug temperature can be made to match the glow plug set temperature Tg1°C, as shown by the broken line, and the ignition performance can be improved more completely.

In addition, in the case where the same diesel engine is used by switching between light oil and alcohol depending on the driver's choice, the glow plug setting temperature when using light oil as fuel and the glow plug setting temperature when using light oil as fuel as shown in Figure 12. The main controller 29 stores both of the glow plug set temperatures when alcohol is used as fuel as shown in Figure 2, and the main controller 29 is set according to the type of fuel actually used.
It is preferable to switch the glow plug setting temperature applied to the control box 22 from the above. However, since light oil has better ignitability than alcohol, the glow plug may be energized only in the light load range.

[Brief explanation of the drawing]

FIG. 1 is a system configuration diagram of a diesel engine equipped with a glow plug control device according to the present invention. FIG. 2 is a diagram showing the characteristics of the glow plug set temperature after a complete explosion of the engine shown in FIG. 1 with respect to the engine load. FIG. 3 is a diagram showing the power consumption of the glow plug when the glow plug temperature is controlled at the glow plug setting temperature shown in FIG. 2 and the power consumption according to the conventional control method with respect to the engine load. FIG. 4 is a diagram showing an example in which the characteristics of the glow plug set temperature with respect to the engine load are corrected according to the engine speed. FIG. 5 is a diagram showing the characteristics of the switching load with respect to the engine speed when correction is performed according to the engine speed as shown in FIG. Figure 6 shows the characteristics of the switching load with respect to the engine speed.
FIG. 7 is a diagram showing an example of correction according to intake air temperature. Figure 7 shows the characteristics of the switching load with respect to the engine speed.
It is a figure which shows the example which correct|amended according to the warm-up dust of an engine. Figure 8 shows the control in which the throttle valve is closed to speed up the rise in glow plug temperature when the engine load changes from a high load side to a low load side and becomes below the switching load. , is a diagram showing the characteristics of glow plug temperature, throttle valve opening, engine load, and accelerator opening with respect to time. FIG. 9 is a diagram showing the characteristics of the throttle valve opening degree with respect to the switching load when the throttle valve control as shown in FIG. 8 is performed. FIG. 1O is a diagram showing the characteristics of the calibration valve closing operation time with respect to the engine rotation speed when the throttle valve control as shown in FIG. 8 is performed. Figure 11 shows the glow plug set temperature and the glow plug temperature when the glow plug temperature is controlled to be increased while the throttle valve is closed in order to prevent the glow plug temperature from decreasing when the throttle valve is restarted. , and the operating state of the throttle valve. FIG. 12 is a diagram showing the characteristics of the glow plug set temperature at the time of startup versus time of a conventional glow-assist diesel engine that uses light oil as fuel. FIG. 13 is a diagram showing the characteristics of the glow plug required temperature with respect to the engine load of a glow-instance diesel engine that uses methanol or the like as fuel. DE...Diesel engine, A, [3, C, D...
- 1st to 4th cylinders, Ila to Ild... 1st to 4th glow plugs, 15... Battery, 21... Electromagnetic switch, 22... Control box, 23... Power transistor, 29 ...Main controller.

Claims (1)

[Claims] (1) In a diesel engine equipped with a glow plug that assists in fuel ignition, an engine load detection means detects the engine load, and the glow plug is energized up to a load range of medium load or higher, and the load detection means detects the engine load. In a low load area where the engine load is below a predetermined value, the glow plug reaches a predetermined high temperature, while in a high load area where the engine load exceeds the predetermined value, the glow plug is heated to a predetermined low temperature. 1. A glow plug control device for a diesel engine, comprising glow plug temperature control means for controlling temperature.