JPS5982564A - Intake heater and its temp. control device - Google Patents

Abstract

PURPOSE:To use an intake heater near its limit of thermal resistance by forming the heater by ceramics and by controlling the voltage impressed on the heater on the basis of the data obtained through direct sensing of heater temperature. CONSTITUTION:A heater 10 is given a rod form and enclosed in a cylindrical holder 13 from the gasification end 11 to combustion end 12. The heater 10 is formed by ceramics by means of hot press, and inside it two elements are installed by means of printed wiring, where one is a pyrogenic resistance 14 consisting of tungsten and the other, a thermo-couple 15. The thermo-couple 15 can inform the temp. of the heater accurately by sensing it directly with its electromotive force, and through monitoring in the ceramics can be used near its limit of thermal resistance. Thereby heating of suction gas can be made in good performance to ensure enhancement of the starting characteristics of engine.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an intake heater that heats the intake air flowing through the intake system of an internal combustion engine such as a diesel engine to improve the startability of the engine. Furthermore, the present invention relates to an intake heater and its temperature control device, which allows the heater to be used near its heat resistance limit by directly detecting the temperature of the molded ceramic heater and controlling the voltage applied to the heater.

[Prior art [1] In general, in internal combustion engines, and in particular diesel engines, when the temperature of the air being taken into the engine is in an environment where the temperature is relatively low (such as cold weather, cold weather, etc.), the internal combustion engine, in particular, is Since the engine cannot induce spontaneous ignition, 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. A starting assist device called an intake heater 3 is installed to improve the starting performance of the engine 1 by heating the intake air.

Conventionally, the one shown in FIG. 2 has been known as this type of take/take heater. Heat generating resistor 4 made of nichrome wire
is inserted into a metal shaft 5 made of steel, and the metal shaft 5 is further compactly filled with magnesium powder 6. Then, the voltage of the power source 7 is applied to the heating resistor 4, and the metal shaft 5
The fuel is made red hot, and fuel is supplied to it 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 shaft 5) and the fuel is directly combusted, the voltage value (current value) of the heating tank is limited due to oxidation and melting of the metal.

(2) Alternatively, the heating resistor 4 indirectly heats the metal shaft 5 via the magnesium powder 6 filled in it to increase the heat capacity of the heater 3 to maintain combustion. As a result, the heating time and the time required to reach the ignition temperature become longer, making it impossible to shorten the starting time. By the way, the time required for large diesel engines was more than 12 seconds.

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

(4) When manufacturing the heater 3, the metal shaft 5 is filled with Magneto/Ram powder 6, so the pitch of the heating resistor 4 may be uneven, making it impossible to obtain an accurate pitch, or the sheath 5
Due to its structure, the heater 3 may be short-circuited, causing local overheating or insufficient heating in the heater 3, burning too much oxygen in the intake system 2, resulting in an oxygen-deficient state, or not being able to heat the entire heater 3 sufficiently. . In addition, uniform heating was not possible due to the uneven pinching of the heat generating resistor 4, and as a result, a constant low voltage was applied, making it basically impossible to control the temperature by changing the applied voltage to maintain the temperature at a high temperature. Therefore, the complete explosion period was prolonged, misfires were likely to occur, and smooth starting performance was not achieved.

[Purpose of the invention]

The present invention was devised in view of the above-mentioned problems, and its purpose is to form the entire heater with ceramic, install a tungsten heating resistor inside the heater, and directly control the temperature of the heater. By detecting and controlling the applied voltage, it is possible to use ceramics near their heat-resistant limit temperature, which in turn significantly shortens heating time and improves startability as much as possible. To provide temperature control equipment.

[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 by hot-pressing and crimping the split ceramic body on which the resistive heating elements are printed, so that a ceramic heater without any irregularity in the pitch of the resistive heating elements is formed. At the same time as the resistance heating element,
A thermocouple made of a homogeneous material, such as tanogsten-tungsten molybdeno, is also printed and embedded to sense the temperature of the heater directly rather than indirectly. By forming such a heater, it becomes possible for the first time to open the temperature side 1 by voltage with high precision.

Further, an applied voltage switching means is connected to the heating resistor of the heater for selectively applying a high voltage to rapidly raise the temperature of the resistor and a low voltage to avoid a rapid temperature drop due to intake air when the air is cold. This switching means is controlled so that the electromotive force obtained from the thermocouple always indicates a constant value, and is switched by a control circuit whose control output is the difference voltage between this electromotive force and the constant value. , the intake heater can be maintained within a constant high temperature range.

[Embodiments of the invention]

Hereinafter, a preferred embodiment of the intake heater according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 3 is a schematic cross-sectional view showing one embodiment of the present invention.

As shown in the figure, the heater 1o 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 is entirely molded from ceramic by hot pressing, and has two insides.
Two elements are internally installed using printed wiring and the like. 1 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 molybdeno, and since what we want to know is the maximum temperature of the heater, The hot junction 15a is placed at the location where the temperature should be the highest among the 10. 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 and constantly maintains the entire heater 10 at a high temperature to continue stable combustion. It has the function to Also,
This ceramic also has the function of protecting the heating resistor 14 inside, preventing oxidation of tungsten due to rapid temperature rise, and shortening 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. It has a function of rapidly heating the ceramic to instantly 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 heater 10, which is rising, by a change in resistance or a change in the current flowing through it, but directly detects the temperature of the heater by using its electromotive force. It has the ability to accurately detect and monitor ceramics to allow them to be used close to their heat resistance limits.

Figure 4 shows such a ceramic intake heater 10.
This shows the temperature rise characteristics of . This is an example in which the sample was molded into a rectangular parallelepiped with a cross-sectional area of 16 myl and a length of 5 Qmm, and measured at room temperature. According to this, when a battery voltage of 24V for large automobiles is applied to the heater 10, it takes only 1.9 seconds.
It can be seen that the ignition temperature T of the fuel reaches 800° C. with EC, and exhibits such a steep temperature rise characteristic that it directly exceeds the heat resistance limit temperature TL of ceramics. On the other hand, if 9.5 V, which is lower than the battery voltage, is applied, the saturation temperature TS will be 9.5 V.
It has a value very close to the heat-resistant limit temperature TL of 86°C, and exhibits a slower rise characteristic compared to the case of 24V, and it takes 12.5 seconds to reach the ignition temperature TF. The voltage that causes the heater 1o to move out rapidly in this way is called a high voltage VH, and the voltage that saturates to a value close to the heat-resistant limit temperature TL at or below the heat-resistant limit temperature TL even if continuously applied is called a low voltage VL.

FIG. 5 is a circuit diagram showing an embodiment of such a temperature control device for the intake heater 1o.

In the heating resistor 14 installed inside the intake heater 1o,
An applied voltage switching means 17 which is switchably controlled by an external signal is connected. A high voltage power source 18 and a low voltage power source 19 to be selectively applied to the heating resistor 14 are connected to two contacts of the switching means 17. Further, a thermocouple 1-5, which is also provided inside the heater 10, is connected to a control circuit 20 provided outside. This control circuit 2o 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, a high voltage vH application signal is generated to the applied voltage switching means 17, and conversely, when the amplified output is larger than a predetermined value VR, a low voltage VL application signal is generated. It is configured.

The predetermined value VR is set to a voltage value corresponding to the ignition temperature TF of the fuel supplied to the intake heater 10. However, the applied voltage switching means 17 is just one example and is not limited to this. For example, if the power source is one high voltage power source 18 and a low voltage VL application signal is sent out, this is not the only example. It is also possible to adopt a configuration in which a resistor for voltage drop is inserted in series with.

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

When you first turn on the control device, Innotheque Heater 1
Since the temperature at 0 is low and the electromotive force of the thermocouple 15 is also low, the control circuit 20 outputs a high voltage application signal, and the applied voltage switching means 17 applies the high voltage VI+ to the heating resistor 14. By applying this high voltage V1, the intake heater 10
As mentioned above, by using tungsten as the heating resistor 14, it is rapidly heated and reaches the ignition temperature TF of 800° C. in only 19 to 2.0 seconds. When the hottest part of the heater 10 reaches the ignition temperature TF, the thermocouple 15 is turned on? Since the force matches the predetermined value VR of the comparator 220, the control circuit 20 immediately generates a low voltage and pressure application signal and applies it for 1h, switching the pressure switching means 17 to
A low voltage V is applied to the heater 10 instead of a high voltage VH.

Apply. This low voltage application is different from the high box pressure application because the cold air in the intake system cannot completely replenish the heat taken away from the intake heater 10 exposed to it, so the ignition temperature T
Although F cannot be maintained and drops, the slope of the drop can be made much smaller than in the case of no voltage. Moreover, if the ignition temperature drops below TF, the control device will operate again and switch to high voltage VII application.
Temperature fluctuations can be kept as small as possible. In this way, the high voltage V11 and the low voltage ■ are alternately applied to the heating resistor body 14 of the intake heater 10, and even when the high voltage ■IT is OFF L, it is heated by the low voltage VL. Therefore, it is possible to converge and maintain the intake heater 10 at 71 m degrees within an extremely high temperature range that is higher than the ignition temperature TF and is the ceramic heat resistance limit 1 crystallinity TI. When the temperature reaches the ignition temperature, the fuel ignites and starts to burn, so the heater 10 receives two types of heat: heating by this combustion and heat generated by the applied voltage, but the hot junction 15a of the thermocouple 15 has the highest temperature. Since the maximum temperature of the heater 10 is always directly monitored, it is possible to effectively avoid entering the ceramic heat resistance limit temperature TL due to a slight control delay when applying a high voltage vH. Therefore, it becomes possible to use ceramics close to their heat resistance limits.

The heater 10 can be maintained at as high a temperature as possible because the main body of the heater 10 is molded from ceramic, the tungsten is prevented from oxidation to ensure nonflammability, and the temperature of the heater 10 is controlled by the thermocouple 15. This becomes possible only through direct detection.

〔Effect of the invention〕

In short, the present invention provides the following excellent effects.

(1) By using tungsten for the heating resistor and embedding it directly in ceramic, which is an insulator, and shielding it from the outside air, it is possible to achieve rapid Jj lFFm and high temperature maintenance. Still, by making the heater entirely ceramic, hot press molding can be performed, so the resistance heating element can be printed wiring, and the heater can be heated uniformly, making it possible to control the temperature by controlling the applied voltage. Furthermore, by directly embedding the thermocouple in the ceramic like the heating resistor, it is possible to accurately detect the Vu+ degree of the heater.

In particular, if the metal of the thermocouple is made of the same material as tungsten, it can be molded under the same conditions as the heating resistor, which simplifies the molding of the heater.

(2) Since the thermocouple installed inside the heater can accurately detect the temperature, ceramic can be used close to its heat control limit. Further, by controlling the application of high voltage and low voltage alternately while monitoring the heater temperature with a thermocouple, the temperature fluctuation is small and high temperature can be maintained. Therefore, since combustion is ensured and good intake air heating can be performed, engine startability is improved as much as possible.

[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 cross-sectional view of a conventional intake heater, and Figs. 3 to 5 show preferred examples of the present invention - actual guns. FIG. 3 is a schematic sectional view of the intake 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 innotheque heater, 14 is a heating resistor, 15 is a heat couple, 16 is a fuel, 17 is an applied voltage switching means, 20 is a control circuit, vl
(is high voltage and VL is low voltage. Patent applicant: Attorney at Isuso Jidosha Co., Ltd. = Nobuo Kinutani

Claims (2)

[Claims] (1) In an intake heater that generates heat by applying voltage to the heater, the generated heat ignites the fuel supplied to the heater, and heats the intake air flowing through the intake system of the internal combustion engine. An intake heater characterized in that it is molded and that a heating resistor made of tungsten and a thermocouple for detecting the temperature of the heater are installed inside the heater. (2) In an intake heater that generates heat by applying a voltage to the heater, the generated heat ignites the fuel supplied to the heater, and heats the intake air flowing through the intake system of the internal combustion engine. At the same time, a heating resistor made of tungsten and a thermocouple for detecting the temperature of the heater are installed inside the heater, and applied voltage switching means for selectively applying a low voltage and a high voltage to the heating resistor. A temperature control device for an intake heater, characterized in that the switching means is connected to a control circuit that follows the temperature of the heater and switches according to changes in the electromotive force obtained by the thermocouple. .