JPH0259300B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to fuel control of 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. In particular, we have developed an intake heater that shortens heating time, maintains high temperature, and provides smooth starting performance by molding the heater with ceramic and controlling the applied voltage to the molded ceramic heater. The present invention relates to a temperature control device.

[Prior Art] In general, in internal combustion engines, and diesel engines in particular, when the temperature of the air being taken into the engine is in a relatively low environment, such as in a cold region or during a cold period, spontaneous ignition occurs due only to the compression of the intake air in the cylinder. This makes it almost impossible to start the engine smoothly.

In order to deal with this situation, as shown in Fig. 1, fuel is supplied to the intake system 2 of the engine 1, and a part of the intake air flowing in as shown by the white arrow in the figure is combusted. A starting assist device called an intake heater 3 is installed, which improves the startability of the engine 1 by heating circulating intake air using combustion heat.

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 heating resistor 4 applies a voltage from the power supply 7 to make the metal sheath 5 red-hot,
Fuel is supplied to this to vaporize it and ignite it for combustion.

[Problem to be solved by the invention] However, such conventional intake
The heater 3 had the following problems.

(1) A metal sheath 5 is used for the heater body, and since fuel is poured directly onto it for combustion, the voltage value (current value) for heating from the point of oxidation and melting of the metal
is subject to restrictions.

(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 down 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 overheated 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 heat generating 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. Therefore, the complete explosion period was prolonged and misfires were likely to occur, making it difficult to obtain smooth starting performance. Furthermore, in the heating element temperature control device disclosed in Japanese Patent Application Laid-open No. 57-193753, control is not performed based on the key switch position or engine speed, which leads to an increase in power consumption of the heating element due to unnecessary heating. I was afraid.

The present invention is aimed at solving the above-mentioned problems. Specifically, if the key switch is not in the starting position after a predetermined period of time from the time when the first rated voltage is applied, the high voltage application is canceled. This prevents unnecessary heating of the intake heater, reduces power consumption, and improves the intake heater.
In order to extend the life of the heater, even if the key switch is returned from the starting position to the on position after the predetermined time, if the engine speed is above a predetermined value, the high voltage application release prohibition circuit An intake heater that maintains a high voltage applied to the intake heater so that even if the engine has already been completely exploded within the predetermined time, the intake heater continues to heat the intake air to ensure a smooth start. The purpose of the present invention is to provide a temperature control device.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides an intake heater for heating intake air of an internal combustion engine, and applying a high voltage to the intake heater when the engine temperature is below a predetermined value, A control circuit that applies a rated voltage when the ignition temperature of the intake heater reaches a predetermined value, and a high voltage that releases the high voltage application if the key switch is not in the starting position after a predetermined time from when the rated voltage is first applied. The high voltage application release circuit is provided with an application release circuit and a high voltage application release prohibition circuit that prohibits the release if the engine speed is equal to or higher than a predetermined value after the predetermined time.

[Function] If the key switch is not in the starting position after a predetermined period of time after the first rated voltage is applied, the high voltage application is canceled and unnecessary heating of the intake heater is prevented, resulting in a reduction in power consumption. In addition to improving the life of the intake heater, even if the key switch is returned from the starting position to the on position after the predetermined time, if the engine speed is equal to or higher than the predetermined value, the high voltage application is stopped. Since the high voltage application to the intake heater is maintained by the release prohibition circuit, even if the engine has already been completely exploded within the predetermined time, the intake heater continues to heat the intake air.
A smooth start can be ensured.

[Embodiment] Hereinafter, a preferred embodiment of the intake heater temperature control device according to the present invention will be described in detail with reference to the accompanying drawings.

As shown in FIG. 3, an intake heater showing an embodiment of the present invention 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. ing.

The intake heater 10 is entirely formed of ceramic by hot pressing, and has a heat generating resistor 14 made of tungsten installed therein through printed wiring or the like. Ceramic has a large heat capacity, and while it emits the heat generated by the heating resistor 14 from the outer peripheral surface of the intake heater 10, it retains a large amount of heat within itself, and constantly maintains the entire intake heater 10 at a high temperature, making it stable. It has a function that allows continuous combustion.

This ceramic also has the function of protecting the heating resistor 14 inside, preventing tungsten from oxidizing due to rapid temperature rise, and improving the heating time of the intake heater 10 as much as possible. ing.

On the other hand, tungsten has the property of rapidly increasing its own resistance value as the temperature rises and generating high heat, and when voltage is applied, it quickly heats ceramic with a large heat capacity and heats up the surface of the intake heater 10. It has a function of instantaneously raising the temperature and vaporizing or igniting the supplied fuel 15.

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, the intake
When a battery voltage of 24V for large automobiles is applied to the heater 10, the ignition temperature of the fuel is reached in 1.9 seconds.
It can be seen that the temperature rise characteristic is so steep that it reaches a TF of 800℃ and directly exceeds the heat resistance limit temperature TL of ceramics.

On the other hand, when 9.5V, which is lower than the battery voltage, is applied, the saturation temperature TS is extremely close to the heat-resistant limit temperature TL of 986℃, and 24V
It shows a slower rise characteristic compared to the case of , and it takes 12.5 seconds to reach the ignition temperature TF. The voltage that rapidly raises the temperature of the intake heater 10 in this manner is referred to as 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 referred to as a rated voltage VN.

FIG. 5 shows a system circuit 16 that controls the voltage applied to intake heater 10. FIG.

Two intake heaters 10 connected in parallel
_is connected to _a parallel circuit consisting of relay X ₁ contact and relay X ₂ contact, and by energizing relay R
The rated voltage VN is applied through the The sensing resistor S/R connected in series to the intake heater 10 is a heater temperature detection element 18 that senses the surface temperature of the intake heater 10, and its resistance value changes in proportion to the temperature of the heating resistor 14. However, since the current changes in response to this change, the above resistance S/R due to this current changes.
The temperature of the intake heater 10 is equivalently sensed by detecting the voltage generated across the intake heater 10.

Key switch 19 connected to battery 17
is adapted to be able to supply the battery 17 voltage from the terminal to the control circuit 20 of the system circuit 16 in the ON position, that is, the ON position shown. The key switch 19 is also in the starting position, that is, as shown in the figure.
In the ST position, starter relay _X5 is energized, its contacts are closed, and starter motor 21 is driven. The switch connected to the terminal is a water temperature detection element 22 that detects the temperature of the cooling water of the internal combustion engine.
When the water temperature T _W indicates a predetermined temperature T _WO , for example, 5°C or less, it turns ON and outputs “0”.
Conversely, when the temperature is 5°C or higher, it turns off and outputs "1". Reference numeral 23 denotes an engine rotation speed detector, which is configured to output a "1" signal when the engine reaches a predetermined rotation speed NS, for example 1000 rotations or more, and output a "0" signal when it is lower than that. Also,
L is a monitor lamp which will be described later.

FIG. 6 shows the control circuit 20 in detail, and in the figure, the control circuit 20 is a portion surrounded by a dotted line.

As shown in _the figure, the terminal connected to the output of the water temperature _sensing element ₂₂ is connected _{to the} terminal via _{a relay} connected to relay _x1 . This relay X ₁ circuit 24 is connected to the water temperature detection element 22
When the sensor detects a temperature below 5°C, the detection output value becomes "0", so it operates to turn on the driver _G6 , and when the key switch 19 is in the ON position, it has the function of energizing the relay _X1 . and,
The energization of this relay X ₁ closes its contact x ₁ ,
High voltage VH is applied to intake heater 10. By the above, relay X ₁ circuit 2
4. A relay contact circuit consisting of a relay X ₁ , a battery 17, and a relay contact x ₁ is formed.

The monitor lamp L connected to the control circuit terminal leads to a lamp circuit consisting of gates G ₇ and G ₈ and driver G ₉ connected to the gate G ₅ output of the relay X ₁ circuit 24, and basically is a relay
It turns on and off according to the excitation and demagnetization of _X1 .

Terminals 11 and 13 connected to both ends of the sensing resistor S/R are connected to a Schmitt circuit 25 within the control circuit 20, and the circuit output is connected to the relay _X1.
It is connected to gate G ₂ of circuit 24. When the Schmitt circuit 25 receives from the sensing resistor S/R an input voltage corresponding to 800°C, at which the ignition temperature TF of the intake heater 10 is a predetermined value, the Schmitts circuit 25 turns on and returns to "0" above that voltage value. If the output is lower than that, it is turned off and outputs "1". In addition, to prevent malfunction, the input voltage corresponding to 800℃ is turned off.
Hysteresis is provided by turning on the input voltage corresponding to 700°C.

When the output value generated at the sensing resistor S/R reaches 700℃, gate _G2 is closed and relay _X1
It is adapted to turn off circuit 24 and deenergize relay _X1 . Also, if the output value drops below 800℃, change the output from “0” to “1” and gate it.
Works to open _G2 . Therefore, the Schmitt circuit 25 has the function of controlling the relay _X1 circuit 24 on and off in accordance with the temperature of the intake heater 10.

On the other hand, the ON position of key switch 19 is
A gate G ₁₀ is connected through a terminal of the control circuit 20 to an automatic voltage regulator 53 that supplies a power supply V _CC to the gate group and a reset output of a flip-flop circuit to be described later, and also drives a relay X ₄ .
Relay X ₄ of the circuit consisting of driver G ₁₁ and driver G 11 is connected to the contacts x ₄ of relay X ₄ which leads to relay X ₂ through its gate G ₁₀ input and terminal. Therefore, when the key switch 19 is turned on, the power supply V _CC is supplied to the control circuit 20 and the relay is turned on.
X ₂ is excited, its contact x ₂ is closed, and the rated voltage VN continues to be applied to the intake heater 10. Of course, the relay contact x ₂ circuit is connected in parallel with the relay contact x ₁ circuit, and when this relay contact x ₁ circuit is turned on, it short-circuits the relay contact x ₂ circuit, so when the relay contact x ₁ is closed, the intake A high voltage VH is applied to the heater 10 instead of the rated voltage VN.

In this way, the reason why the _two relay contacts are always on when the key switch 19 is turned on is to prevent the intake heater 10 from becoming de-energized during the switching interval between the rated VN and high voltage VH. This is to do so. Therefore, key switch 1
9 is in the ON position, relay X ₂ is always energized, so the scimit circuit 25
If the X ₁ circuit 24 is turned off and the relay X ₁ is deenergized,
The rated voltage VN is applied to the intake heater 10 instead of the high voltage VH. Furthermore, conversely, if relay X ₁ is energized, the intake
A high voltage VH will be applied to the heater 10.

By the above, the Schmitt circuit 25, the gate
G ₁₀ , G ₁₁ , relay x ₄ , relay contact x ₄ , relay x ₂ ,
A switching circuit consisting of a battery 17 and _two relay contacts is formed. Furthermore, if the switching time is extremely fast and the interval can be ignored, the method of constantly applying the rated voltage may not be adopted, but the rated voltage VN and the high voltage VH may be alternately switched and applied.

In order to deactivate the entire control circuit 20 without turning off the power supply V _CC , three systems of release circuits 26 are provided.
A release circuit 26 consisting of a, 26b, and 26c is provided within the control circuit 20. The release circuit 26a of the first system is connected from a terminal to a gate _G12 which opens for 0.5 seconds when the key switch 19 is turned on, a set input of a common flip-flop FF1 via a trailing edge activated differentiator _D1 and a gate _G13 . It is wired to enter gate G ₁₄ , which is connected to . The output Q of this common flip-flop FF1 is connected to the gate _G5 of the relay _X1 circuit 24, the gate _G15 for controlling the supply of fuel to the intake heater 10, and the gate _G10 of the relay _X4 circuit.

Therefore, when the input value from the terminal is "1", the first system release circuit 26a has a function of generating a set signal for the flip-flop FF1 0.5 seconds after turning the key switch 19 to the ON position. This set signal causes the output Q to become "0", demagnetizing the relays X ₁ , X ₂ and X ₄ and disabling the function of the control circuit 20.

In addition, the second system release circuit 26b is connected to a common terminal via a terminal connected to the ST position of the key switch 19, a 30-sec timer 27 activated at the trailing edge, a differentiator D ₂ and a gate G ₁₆ , which are also activated at the trailing edge. Connected to gate G ₁₄ . Therefore, after 30 seconds have passed since the key switch 19 was returned from the ST position to the ON position, the flip-flop FF is activated.
It has the function of setting 1.

Further, the third system cancellation circuit 26c includes a trailing edge activated differentiator D ₃ which has the same input as the second system.
and terminal 1 connected to the output of the circuit consisting of gate G ₁₇ and the output of engine speed detector 23.
2 through gate _G18 is input to a common gate _G19 , whose common gate output is connected to a common gate _G14 forming a set input. Therefore, this third system release circuit 26c
has the function of immediately generating a set signal when the key switch 19 is returned from the ST position, unless the engine speed has reached a predetermined speed NS, and inputting the set signal to the flip-flop FF1. Control circuit 20 is deactivated.

An _X1 demagnetization adjustment circuit 50 is connected to the gate _G4 of the relay _X1 circuit 24 to demagnetize the relay X1 after a certain period of time has passed since the key switch ₁₉ is turned to the ON position, except in certain cases. . This circuit passes from the terminal through a 0.5 sec timer 28, a trailing edge activated 10 sec timer 29, a trailing edge activated differentiator D ₄ , gates G ₂₀ and G ₂₁ ,
A degaussing circuit 51 as a high voltage application release circuit leading to the set input of the flip-flop FF2, and gates G 22 and G receiving two signals from the terminal connected to the ST position and the terminal 12 connected to the output of the engine rotation speed detector ₂₃ . ₂₃ , and a demagnetization inhibiting circuit 52 as a high voltage application release inhibiting circuit whose output is connected to the gate _G21 connected to the set input of the flip-flop FF2. Therefore, _this relay
9 is in the ST position or the engine speed has reached a predetermined speed NS or higher, the gate _G4 is forcibly closed and the excitation of the relay _X1 is released.

In addition, in FIG. 6, 30 is a disconnection detection circuit,
The configuration is almost the same as the above Schmitt circuit 25,
The input is also common, and has the function of outputting a "1" output in synchronization with the Schmitt circuit 25 outputting a "0" output when the intake heater 10 is normal. The output of this disconnection detection circuit 30 is the gate
Connected to the gate G ₇ of the lamp circuit through G ₂₄ . Therefore, the gate G ₇ remains open while the intake heater 10 has not yet reached the ignition temperature TF of 800°C, but after the temperature reaches 800°C for the first time, the gate G 7 becomes the "1" output from the disconnection detection circuit 30. Since the monitor lamp L is then closed, the monitor lamp L remains off despite the second and subsequent energization of the relay _X1 .

Furthermore, in FIG. 6, 31 is a fuel circuit that controls fuel supplied to the intake heater 10, and relay _X3 is a relay for the fuel pipe.

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

First, the key switch 19 is switched from the OFF position to the ON position when starting the engine. This switching activates the automatic voltage regulator 26, which supplies the power supply V _CC to the control circuit 20 and also connects the two flip-flops FF1 and FF.
A reset signal is sent to both Q outputs to set them to "1". At the same time, relay _X4 circuit operates to excite relay _X2 . Here, if the cooling water of the internal combustion engine is higher than the predetermined value of 5°C, the output value of the water temperature detection element 22 becomes "1" and the gate _G2 of the relay _X1 circuit ₂₄ is closed. A 0.5sec width pulse signal from 28 is input, turning on driver G ₆ , relay X ₁ and monitor lamp L.
is excited and lit for 0.5 seconds. Similarly, relays X ₂ and X ₄ are also excited for 0.5 seconds.
The reason why the relays X ₁ , X ₂ , X ₄ and the monitor lamp L are demagnetized and turned off after 0.5 seconds is because a set signal is formed in the release circuit 26a of the first system, which activates the total applied voltage release circuit 26 and turns off the flip-flop FF1. This is because the Q output is set from "1" to "0" and the gates _G5 and _G10 of the relay _X1 circuit 24 and the relay _X4 circuit are closed. Therefore, when the cooling water temperature is equal to or higher than the predetermined value _TWO of 5°C, the monitor lamp L is lit for only 0.5 seconds, which is the standby time, after the ON signal of the key switch 19 is turned on, and thereafter the control circuit 20 is turned off. It becomes virtually inactive. This allows the driver to immediately move the key switch 19 to the ST position and start the engine after waiting for 0.5 seconds. It is known that if the temperature of the cooling water is 5° C. or higher, there is no need to heat the intake air by igniting the intake heater 10, and smooth startability can be ensured. For this reason, the control circuit 20 is deactivated. is desirable from the standpoint of energy conservation.

When the cooling water temperature of the internal combustion engine is below the predetermined value _TWO of 5°C, the output of the Schmitt circuit 25 is "1" because the temperature of the intake heater 10 is low, and the gate _G12 connected to the terminal is Instead of closing, gate _G2 of relay _X1 circuit 24 opens, immediately energizing relay _X1 and
Apply high voltage VH 24V through its contact _x1 to. At the same time, the lamp circuit also responds and the monitor lamp L lights up. During the initial application time Tm of 24V shown in the time chart of FIG. 7, by using tungsten as the heating resistor 14, the intake heater 10 reaches 800°C, which is the predetermined value of the ignition temperature TF, as described above. Although the time required for this is extremely short and its value is 1.9 to 2.0 seconds, it is equivalent to this time. That is, as the voltage of the battery 17 is directly applied to the intake heater 10, its temperature rises rapidly, but at the same time it reaches 800°C, its output value is detected by the sensing resistor S/R, and the Schmitt circuit 25 outputs. is inverted and changes from “1” to “0”. To be exact, it turns out to be 700 degrees Celsius, but
Here, for convenience, 800°C is assumed to be the switching point. This reversal closes gate G ₂ of relay X ₁ circuit 24, demagnetizes relay X ₁ , opens its relay contact circuit, and energizes _the relay contact circuit of relay 1
0, the rated voltage VN of 9.5V is applied after 1.9 to 2.0 seconds instead of the high voltage VH of 24V. This switching prevents the intake heater 10 from reaching the ceramic heat resistance limit temperature TL of 1100°C. Also, unlike high voltage VH, rated voltage VN
Since the voltage value is low, the intake heater 10 exposed to the cold air of the intake system after 9.5V is applied loses heat and its temperature begins to drop. The drop is the ignition temperature
When the temperature of TF reaches 800℃, Schmitt circuit 2 is activated again.
5 operates, inverting its output from "0" to "1" and energizing relay _X1 . In this way, depending on the temperature of the intake heater 10, the voltage applied to the intake heater 10 becomes high voltage.
VH and rated voltage VN are alternately switched. At this time, the monitor lamp L does not light up because the gate _G7 of the lamp circuit is closed by the output "1" of the disconnection detection circuit 30. Therefore, the monitor lamp L is initially lit only once for about 2 seconds, that is, the time Tm until the intake heater 10 reaches 800°C.

In this way, the high voltage VH and the rated voltage VN are applied alternately to the intake heater 10, so unlike the case where the high voltage is simply turned on and off, the high voltage
Since heating is performed at the rated voltage even when VH is turned off, the temperature of the intake heater 10 can be maintained within an extremely high temperature range that is above the ignition temperature TF and below the ceramic heat resistance limit temperature TL. In this way, the fuel supplied to the intake heater 10 evaporates and vaporizes, ignites, and continues to burn, heating the surrounding air.

Next, after confirming that the monitor lamp L has gone out, the driver switches the key switch 19 from the ON position to the ST position to start the engine. As a result of this switching, the starter motor 21 is driven and the engine begins to move, so that the air that had been stopped in the intake system 2 begins to circulate, and the intake air takes away more heat from the intake heater 10. However, in order to counter this heat absorption, the switching circuit's high voltage
The switching time between VH and rated voltage VN is only shorter than when the key switch 19 is in the ON position, and the temperature of the intake heater 10 does not drop and the ignition temperature TF is still maintained.

In this case, after the first high voltage VH is removed,
In other words, after the Tm time has elapsed, the predetermined time indicated by TST in the time chart of Figure 7 is
If the key switch 19 is not switched to the ST position even after 10.5 seconds and the ST signal is not generated,
Since the X ₁ degaussing circuit works preferentially, the relay X ₁ is demagnetized and high voltage VH is applied to the intake heater 10.
The rated voltage VN is simply applied constantly without being applied. After TST time elapses
Even when switching to the ST position, the X ₁ degaussing circuit output remains set and the relay X ₁ is not demagnetized, so the ignition temperature of the intake heater 10
TF will be maintained at the rated voltage alone. If you do not start the engine within the TST time, simply turn on the key switch 1 to listen to the radio.
9 has been turned on, or the engine is not in a hurry to start, and in this case, it is considered that there is no problem even if the above-mentioned procedure is performed. However, even in this case, if the engine has already been started within the TST time and the engine rotation speed N has reached the predetermined rotation speed of 1000 rotations or more, the output of the engine rotation speed detector 23 will be Since it becomes "1", even if the ST signal is not output, the degaussing prohibition circuit 52 consisting of gates _G22 and _G23 is activated and prohibits the input of the set signal to flip-flop FF2, so relay _X1 The degaussing circuit 51 is not activated, and therefore has the same effect as when the ST signal is output.

In this way, the length of time from ON position operation to ST position operation is used as a criterion to determine whether or not to allow the transition to the complete detonation time. I can respond.

Next, the case where the key switch 19 is returned from the ST position to the ON position, that is, the case where the starter motor 21 is once driven and then released will be described. In this case, the second system release circuit 26b is activated by the trailing edge of the ST signal, and all output systems of the control circuit 20 are activated after 30 seconds have elapsed from the trailing edge as the set time for afterglow shown by TH in the time chart of FIG. is inactive.
Therefore, after that, the intake heater 10
Not only is it no longer heated, but the fuel supply is also cut off. This means that after the set time TH for afterglow, that is, 30 seconds, the accelerator pedal has already been pressed, the engine speed is high enough, and the engine temperature is high enough, so there is no problem with spontaneous ignition. This is because the assistance of the intake heater 10 is no longer required, and even if the intake heater 10 were to provide assistance after that, the assistance would be meaningless. Therefore, if the engine speed is below the predetermined speed at the trailing edge of the ST signal, the release circuit 26c of the third system is activated.
is activated, and immediately puts the control circuit 20 into a non-operating state without waiting for 30 seconds to pass. ST
If the engine speed is low at the trailing edge of the signal, it means that the accelerator pedal was not pressed during the ST position, and in such a case there is no room for the engine speed to increase, and the driver abandons the intention to start the engine. This is because it is thought that he did. When the third system release circuit 26c is activated, if it is desired to start the engine again, it is necessary to return the key switch 19 to the OFF position, that is, the OFF position shown in the figure.

Therefore, this total applied voltage release circuit 26, including the above-described first system release circuit 26a, is used in the control circuit 2 when engine starting assistance by the intake heater 10 is not required or is not required at all.
Since 0 is inactive, appropriate starting assistance can be provided and waste can be eliminated.

Further, the control circuit 20 is not limited to the above-mentioned embodiment, and it goes without saying that modifications can be made within the scope of the present invention.

[Effects of the Invention] As described above, the intake heater temperature control device of the present invention controls the intake heater that heats the intake air of an internal combustion engine, and applies a high voltage to the intake heater when the engine temperature is below a predetermined value. The control circuit applies a rated voltage when the ignition temperature of the intake heater reaches a predetermined value, and the high voltage control circuit applies a rated voltage when the ignition temperature of the intake heater reaches a predetermined value. A voltage application release circuit and a high voltage application release prohibition circuit that prohibits the release if the engine speed exceeds a predetermined value after the predetermined time are provided, so that the key switch is activated after a predetermined time from the time when the first rated voltage is applied. When the intake heater is not in the starting position, the high voltage application is canceled and unnecessary heating of the intake heater is prevented, thereby reducing power consumption and extending the life of the intake heater. Even if the key switch is returned from the starting position to the on position, if the engine speed is above a predetermined value, the high voltage application release prohibition circuit maintains the high voltage application to the intake heater. Therefore, even if the engine has already been completely exploded within the predetermined time, heating of the intake air by the intake heater is continued, and a smooth start can be ensured.

[Brief explanation of drawings]

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 7 are diagrams of an intake heater temperature control device according to the present invention. A preferred embodiment is shown in Fig. 3, a schematic sectional view of the intake heater, Fig. 4 a temperature rise characteristic diagram thereof, Fig. 5 a system circuit diagram of the temperature control device, and Fig. 6 the same control circuit. A more detailed system circuit diagram, FIG. 7, is a timing chart of the same. 10... Intake heater, 14... Resistance heating element, 16... System circuit, 18... Heater temperature detection element, 19... Key switch, 22... Water temperature detection element, 24... Relay X ₁ circuit, X ₁ ... Relay, 17 ... Battery, x ₁ ... Contact of relay X ₁ , 25 ... Schmitt circuit, G ₁₀ and G ₁₁ ...
Gate, X ₄ ... Relay, x ₄ ... Contact of relay X ₄ ,
X ₂ ...Relay, x ₂ ...Relay X ₂ contact, 26...
…Switching circuit, S/R…Sensing resistor, VH…
…High voltage, VN…Rated voltage, T _W …Water temperature, TL
...Ceramic heat resistance limit temperature, TF...ignition temperature, TS...saturation temperature. 50... Relay X ₁ demagnetization adjustment circuit, 51... Demagnetization circuit as a high voltage application release circuit, 52... Demagnetization prohibition circuit as a high voltage application release prohibition circuit.

Claims (1)

[Claims] 1. An intake heater that heats the intake air of an internal combustion engine, and when the engine temperature is below a predetermined value, a high voltage is applied to the intake heater, and when the ignition temperature of the intake heater reaches a predetermined value, a rated voltage is applied. a high voltage application release circuit that releases the high voltage application if the key switch is not in the starting position after a predetermined period of time after the initial application of the rated voltage; An intake heater temperature control device comprising a high voltage application release prohibition circuit that prohibits the release.