JPH0156263B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an intake heater for heating intake air flowing through the intake system of an internal combustion engine such as a diesel engine to improve engine startability. This invention relates to an intake heater temperature control device that enables the heater to be used near its heat resistance limit by molding the heater from ceramic and directly detecting the temperature of the molded ceramic heater to control the voltage applied to the heater. .

[Prior art]

In general, internal combustion engines, and diesel engines in particular, are in environments where the temperature of the air being taken into the engine is relatively low (cold regions, cold times, etc.), and spontaneous ignition can occur due to the compression of the intake air within the cylinder. Therefore, it is almost impossible to start the engine smoothly.

To deal with this situation, as shown in Figure 1, fuel is supplied to the intake system 2 of the engine 1 to combust a part of the intake air (white arrow in the figure), and this combustion heat is used to reduce the circulation. Intake heater 3 that improves the startability of engine 1 by heating the intake air
It is equipped with a starting aid called .

Conventionally, this type of intake heater was the second
The one shown in the figure is known. A heating resistor 4 made of nichrome wire is inserted into a metal sheath 5 made of steel, and the metal sheath 5 is further compactly filled with magnesium powder 6. Then, the voltage of the power supply 7 is applied to the heating resistor 4 to make the metal sheath 5 red-hot,
Fuel is supplied to this to vaporize it and ignite it for combustion.

[Problems with conventional technology]

However, such an intake heater 3 has the following problems.

(1) Since metal is used for the heater body (metal sheath 5) and fuel is directly applied to it for combustion, the voltage value (current value) for heating is limited due to the oxidation and melting of the metal.

(2) Moreover, since the heating resistor 4 indirectly heats the metal sheath 5 via the magnesium powder 6 filled to increase the heat capacity of the heater 3 to maintain combustion, the heating time is As a result, it took a long time to reach the ignition temperature, making it impossible to shorten the starting time. Incidentally, large diesel engines took a long time, over 12 seconds.

(3) Due to the current restriction, the overall temperature cannot be made high enough, and the heat capacity of the metal sheath 5 itself is small, so even if ignition occurs, if you try to drive the starter motor to start the engine, Due to the accompanying increase in intake air amount and flow rate, the metal sheath 5 was cooled and often misfired before the engine was started.

(4) When manufacturing the heater 3, the metal sheath 5 is filled with magnesium powder 6, so the heating resistor 4 is
The pitches of the heaters may become uneven, making it impossible to obtain accurate pitches, or short-circuiting may occur within the sheath 5. Due to the structure, the heater 3 may become locally heated or underheated, causing too much oxygen in the intake system 2 to be burned. There was a lack of oxygen, and the entire heater 3 could not be heated sufficiently. Moreover, because the pitch of the heating resistor 4 is uneven, uniform heating cannot be achieved, and as a result, a low voltage is applied at a constant rate, making it basically impossible to control the temperature by changing the applied voltage to maintain the temperature at a high temperature. As a result, the complete explosion period was prolonged, misfires were likely to occur, and smooth starting was not achieved.

Regarding this point, we use a ceramic heater with a tungsten heating resistor embedded in the ceramic, and apply a high voltage to it to quickly raise the temperature to the ignition temperature, while detecting the heater temperature and turning on the applied voltage.・It is possible to maintain the temperature constant by controlling off.

However, this alone cannot maintain the heater temperature as high as the ceramic heat resistance limit temperature.

For example, the ignition temperature is 800℃, and the heat resistance limit temperature of ceramic is 1100℃.By applying a high voltage, ceramic with a large heat capacity is quickly heated, and the surface temperature of the heater is instantly raised to the ignition temperature of 800℃. If so, the temperature rise characteristic must be so steep that it exceeds the heat resistance limit temperature of ceramics, 1100°C. In addition, since the surface temperature of the heater cannot be directly measured and there is a time delay between the actual temperature and the measured temperature, simply controlling the high voltage on and off will result in a large temperature fluctuation range of the heater. For this reason, it is difficult to bring the heater temperature as close as possible to the heat resistance limit temperature of ceramic, 1100°C.

That is, the heater temperature actually tends to reach the heat-resistant limit temperature of the ceramic, causing cracks in the ceramic and causing the tungsten wire to break, resulting in a defective ceramic heater. Furthermore, when exposed to cold air or intake air, the temperature decreases rapidly, significantly lowering the ignition temperature, and it may take a long time to return to the ignition temperature, resulting in failure to ignite.

[Purpose of the invention]

The present invention was devised in view of the above-mentioned problems, and its purpose is to enable ceramics to be used close to their heat-resistant limit temperature, thereby significantly shortening heating time and improving startability as much as possible. An object of the present invention is to provide an intake heater temperature control device that can achieve the following.

[Structure of the invention]

According to the present invention, the above object is achieved as follows. That is, tungsten, which has the property of rapidly increasing its resistance as the temperature rises, is used as a resistance heating element, and can be heated rapidly by applying a voltage. This resistance heating element is directly embedded in the heater body, which is made of ceramic having high heat resistance, high strength, and high heat capacity, without coming into direct contact with oxygen and because ceramic is an insulator. This embedding is carried out, for example, by hot-pressing and crimping a split ceramic body on which the resistive heating elements are printed and bonded, so that a ceramic heater without any irregularities in the pitch of the resistive heating elements is formed. At the same time as the resistive heating element, a thermocouple made of a homogeneous material, for example tungsten-tungsten molybdenum, is also printed and embedded in order to directly, rather than indirectly, detect the temperature at the hottest point along the length of the heater. Formation of such a ceramic heater makes it possible for the first time to control temperature using voltage with high precision.

In addition, the tungsten heat generating resistor of the ceramic heater is supplied with a high voltage that rapidly raises the temperature of the heater via an applied voltage switching means, and a high voltage that is continuously applied to the tungsten heating resistor so that the heater temperature is below and close to the heat resistance limit temperature T _L of the ceramic. Two types of power supplies are connected so that they can be alternately applied: a low voltage V _L that saturates at a value (saturation temperature T _S ). Then, by a control circuit that receives the temperature T detected by the thermocouple and compares it with the ignition temperature T _F of the fuel, when T<T _F , the applied voltage switching means changes to the high voltage side, T≧T _F When , the voltage is switched to the low voltage side.

This allows the temperature of the intake heater to reach the ignition temperature of the fuel in an extremely short period of time due to the high voltage.
T _F is reached, and thereafter, under the application of a low voltage, the temperature is converged and maintained at the saturation temperature T _S , which is below and close to the heat resistance limit temperature T _L of ceramics. Since this temperature is naturally much higher than the ignition temperature T _F , the cold air in the intake system is also heated to a high temperature in a short period of time.

However, when exposed to cold air in the intake system,
It cannot be maintained above the ignition temperature T _F and becomes lower than the ignition temperature T _F , but the above saturation temperature T _S just before that temperature
Moreover, in the temperature range above the ignition temperature T _F , the fall occurs while a low voltage is always applied, so above the ignition temperature T _F the slope of the drop is much greater than when no voltage is applied. It is gradual. Then, when the temperature reaches a lower temperature range than the ignition temperature _TF , high voltage is applied again. The amount of drop below the ignition temperature T _F and the time width until the temperature rises to the ignition temperature T _F are also smaller than when no voltage is applied in the temperature range above the ignition temperature T _F.

[Embodiments of the invention]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of an intake heater temperature control device according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 3 is a schematic sectional view showing an intake heater employed in the present invention.

As shown in the figure, the heater 10 is formed into a rod-shaped body and is surrounded by a cylindrical holder 13 extending from the vaporization end 11 side to the combustion end 12 side. This heater 10
The entire body is made of ceramic by hot pressing, and two elements are installed inside using printed wiring or the like. One is a heating resistor 14 made of tungsten that generates heat by applying a voltage from the outside. One thermocouple 15 is capable of measuring temperatures above room temperature, and is preferably made of the same material as the resistance heating element 14, for example, tungsten-tungsten molybdenum. The hot junction 1 is located at the place where the highest temperature should be inside.
5a. Ceramic has a large heat capacity and releases the heat generated by the heating resistor 14 from the outer circumferential surface of the heater 10, while retaining a large amount of heat within itself, constantly maintaining the entire heater 10 at a high temperature to continue stable combustion. It has the function to This ceramic also has the function of protecting the heating resistor 14 inside, preventing tungsten from oxidizing due to rapid temperature rise, and increasing the heating time of the heater 10 as much as possible. . On the other hand, tungsten has the property of rapidly increasing its own resistance value as the temperature rises and generating high heat. Therefore, by setting the initial value (normal temperature value) quite small and applying voltage, tungsten can be made into a ceramic with a large heat capacity. It has a function of rapidly heating the fuel 16 to instantaneously raise the surface temperature of the heater 10 and vaporizing or igniting the supplied fuel 16. In addition, the thermocouple 15 does not indirectly detect the maximum temperature of the rising heater 10 by a change in resistance or a change in the current flowing through it, but directly detects it by its electromotive force, and accurately determines the temperature of the heater. It has the function of being able to detect heat resistance and, by monitoring it, allow ceramics to be used close to their heat resistance limits.

FIG. 4 shows the temperature rise characteristics of the intake heater 10 made of ceramic. Cross-sectional area 16
^This is an example in which the sample was formed into a rectangular parallelepiped with a size of 60 mm and a size of 60 mm, and was measured at room temperature. According to this, when a battery voltage of 24V for large automobiles is applied to the heater 10, the ignition temperature of the fuel reaches T _F 800°C in just 1.9 seconds, and the heat resistance limit temperature of the ceramic T _L 1100°C is reached in just 1.9 seconds.
It can be seen that the temperature rise characteristic is steep enough to exceed ℃. On the other hand, when 9.5V, which is lower than the battery voltage, is applied, the saturation temperature T _S has a value extremely close to the heat-resistant limit temperature T _L of 986°C, and the rise characteristic is slower compared to the case of 24V. It takes 12.5 seconds to reach the ignition temperature T _F.
In this way, the voltage that rapidly raises the temperature of the heater 10 is the high voltage V _H , and even if it is continuously applied, the heat resistance limit temperature T _L
In the following, the voltage that saturates to a value close to this will be referred to as a low voltage _VL .

FIG. 5 is a circuit diagram showing an embodiment of the temperature control device for the intake heater 10. As shown in FIG.

An applied voltage switching means 17 that is switchably controlled by an external signal is connected to a heating resistor 14 provided inside the intake heater 10 . The two contacts of this switching means 17 include a high voltage power source 18 and a low voltage power source 1 to be selectively applied to the heating resistor 14.
9 is connected. Also, the heater 10
A thermocouple 15 installed inside is connected to a control circuit 20 installed outside. This control circuit 20 consists of an amplifier 21 and a comparator 22, and the amplifier 21 amplifies the thermoelectromotive force obtained by the thermocouple 15, and the comparator 22 compares this amplified output with a predetermined value _VR , When the amplified output is smaller than a predetermined value, the applied voltage switching means 17 is set to the high voltage _VH.
It is configured to generate an applied signal and, conversely, to generate a low voltage V _L applied signal when the amplified output is larger than a predetermined value V _R .

The predetermined value V _R is set to a voltage value corresponding to the ignition temperature T _F of the fuel supplied to the intake heater 10 . Further, the applied voltage switching means 17 is merely an example, and is not limited to this. For example, when the high voltage power supply 18 is directly taken out from the battery and a low voltage V _L application signal is sent out, this It is also possible to create the low voltage power supply 19 by inserting a voltage drop resistor in series.

The operation of the present control device having the above configuration will be explained.

When you first turn on the control device, the intake
Since the temperature of the heater 10 is low and the electromotive force of the thermocouple 15 is also low, a high voltage application signal is output from the control circuit 20, and the applied voltage switching means 17 applies a high voltage V _H to the heating resistor 14. By applying this high voltage _VH , the intake heater 10 is rapidly heated by using tungsten as the heating resistor 14 as described above, and the ignition temperature T _F of 800°C is heated by only 1.9 to 800°C.
Reached in 2.0sec. At the same time that the hottest part of the heater 10 reaches the ignition temperature T _F , the electromotive force of the thermocouple 15 matches the predetermined value V _R of the comparator 22, so the control circuit 20 immediately generates a low voltage application signal. , the applied voltage switching means 17 is switched, and the low voltage V _L is applied to the intake heater 10 instead of the high voltage V _H.
Apply. Unlike high voltage application, this low voltage application cannot completely replenish the heat taken away from the intake heater 10 exposed to the cold air in the intake system, so the ignition temperature T _F cannot be maintained and falls, but no voltage The slope of the descent can be made much smaller than in the case where Furthermore, when the temperature drops below the ignition temperature T _F , the control device operates again and switches to applying the high voltage V _H , so that temperature fluctuations can be suppressed as small as possible. In this way, the high voltage V _H and the low voltage V _L are alternately applied to the heating resistor 14 of the intake heater 10, and even when the high voltage V _H is turned off, it is heated by the low voltage V _L. Therefore, the temperature of the intake heater 10 must be above the ignition temperature T _F and the ceramic heat resistance limit temperature.
Convergence can be maintained within an extremely high temperature range below T _L.

In this case, when the heater 10 reaches the ignition temperature, the fuel ignites and starts burning, so the heater 10 receives two types of heat: heating from this combustion and heat generated from the applied voltage.
Since the hot junction 15a of No. 5 is installed at the highest temperature point and constantly directly monitors the maximum temperature of the heater 10, when a high voltage V _H is applied, the ceramic heat resistance limit temperature T _L is caused by a slight control delay. This makes it possible to effectively avoid the intrusion into heat, making it possible to use ceramics close to their heat resistance limits.

The heater 10 can be maintained at as high a temperature as possible in this way because the main body of the heater 10 is molded with ceramic, the tungsten is prevented from oxidation to ensure nonflammability, and the thermocouple 15 is used to maintain the heater 10 at the highest possible temperature. This becomes possible only by directly detecting temperature.

〔Effect of the invention〕

In summary, the present invention exhibits the following excellent effects.

(1) The temperature of the intake heater can be raised to the fuel ignition temperature in an extremely short time using high voltage.

After that, the voltage is switched to a low voltage to prevent the heater temperature from reaching the heat-resistant limit temperature of the ceramic, and under the application of this low voltage, the heater temperature is maintained at a saturation temperature close to the heat-resistant limit temperature of the ceramic. be done. This prevents the occurrence of cracks in the ceramic and disconnection of the heating resistor, and the intake air is heated by the intake heater at a temperature higher than the ignition temperature, significantly shortening the heating time and improving startability as much as possible. Improvement can be achieved.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of an engine showing the mounting position of the intake heater, Fig. 2 is a schematic sectional view of a conventional intake heater, and Figs. 3 to 5 show a preferred embodiment of the present invention. , Figure 3 shows the intake
FIG. 4 is a schematic cross-sectional view of the heater, FIG. 4 is a temperature rise characteristic diagram thereof, and FIG. 5 is a circuit diagram of a temperature control device for the intake heater. In the figure, 1 is an internal combustion engine, 2 is an intake system, 10 is an intake heater, 14 is a heating resistor, 15 is a thermocouple, 16 is a fuel, 17 is an applied voltage switching means,
20 is a control circuit, V _H is a high voltage, and V _L is a low voltage.

Claims (1)

[Claims] 1. An intake heater provided in an engine intake system,
A tungsten heating resistor is embedded in ceramic, and a thermocouple is embedded in the hottest point in the longitudinal direction of the heater, and a high voltage that rapidly raises the temperature of the heater is applied to the heater via an applied voltage switching means. A low voltage is connected to the power source so that a low voltage that, when continuously applied, saturates the heater temperature at a value that is below and close to the ceramic's heat resistance limit temperature, is connected to the power source, and when the temperature T detected by the thermocouple is detected, this voltage is applied to the fuel. An intake characterized by comprising a control circuit that switches the applied voltage switching means to a higher voltage side when T<T _F compared to an ignition temperature T _F , and to a lower voltage side when T≧T _F. - Heater temperature control device.