JPH0135186B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heating control device for a preheating plug (glow plug) used to facilitate the starting of a cold engine (particularly a diesel engine), and particularly relates to a heating control device for a preheating plug (glow plug) used to facilitate starting of a cold engine (particularly a diesel engine). The present invention relates to a preheating plug heating control device that appropriately controls heating of other preheating plugs even if one of the preheating plugs is disconnected.

Since it is difficult to start a cold engine just by starting the starter, a preheating plug is installed in the engine, and when the engine is started, the preheating plug is heated to a predetermined temperature in the combustion chamber, and then the starter is used to start the engine. There is. The preheating plug must heat up to a predetermined temperature in a very short time when the engine is started, and must maintain that predetermined temperature until the engine has finished starting. A resistance wire is generally used in such a preheating plug, and the resistance wire has a positive temperature coefficient of resistance in order to shorten the preheating time. In order to control the temperature so that the preheating plug is not heated above the scheduled temperature, the resistance value of the preheating plug is detected after electric current is supplied to the preheating plug, and when the resistance value matches the resistance value of the preheating plug at the scheduled temperature, the preheating plug is The current supply to the equipment is stopped.

On the other hand, if multiple preheating plugs are installed in parallel, if the preheating plugs are disconnected, the parallel resistance values of the multiple preheating plugs will change, the temperature control described above will not work smoothly, and the temperature of the preheating plugs will change. The temperature exceeds the planned temperature,
There is a risk that an undesirable situation may occur.

In order to avoid such inconveniences, there is provided a glow plug temperature control device that controls the temperature of glow plugs by detecting and determining the total current value of glow plugs connected in parallel and controlling the same current value.
A preheating control device for a diesel engine has been developed, which includes the temperature control device that detects disconnection of a glow plug and automatically changes the reference level for determining the total current value according to the detected output,
This is disclosed in Japanese Patent No. 26276, but the heating of the preheating plug is performed smoothly only when one preheating plug is disconnected, and the above-mentioned conventional inconveniences have not yet been completely solved. It's not something I did.

Therefore, an object of the present invention is to provide a preheating plug heating control device that can control the heating of the remaining preheating plugs to a predetermined temperature even if any one of a plurality of preheating plugs is disconnected or even if any number of preheating plugs are disconnected. is to provide.

Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a waveform diagram of each part thereof. In the figure, E is a power source, which can be considered as a vehicle battery. The TR is a switching element, and can be an electrical switch made of a semiconductor such as a power transistor, or a mechanical switch such as a relay, which can be selected as appropriate depending on the required operating speed. The control unit 1, which will be described later, causes the switching element TR to cause current from the power source E to flow through the preheating plug GP during its on period, and to stop supplying the current during its off period. GP is a preheating plug (glow plug), and it is provided as many as the number of cylinders in the engine, and in Figure 1 there are 4
Two preheating taps are provided. The preheating plug GP has a metal resistance wire as a heating element, and the resistance temperature characteristic of the resistance wire is positive (that is, the resistance increases as the temperature increases). CC is a constant current circuit that receives a timing pulse TP from the control unit 1 and causes a constant current i to flow through the preheating plug GP during the off period of the switching element TR. AP is a differential amplifier,
It outputs the voltage drop caused by current flowing through the preheating plug GP as a voltage value e _t , and is equipped with input balance resistors R1 and R2. Reference numeral 10 is a set temperature comparison circuit, which selects the desired set preheating temperature (for example, 900
The set temperature and voltage value e _s (=i×r _s ) determined by the resistance value r _s of the preheating plug GP at 30°F (°C) is set or memorized, and the voltage value e _t during the off period output by the differential amplifier AP is set or memorized. The set temperature and voltage values e _s are compared, and if e _t ≧ e _s , a prohibition signal is sent to the switching element control circuit 11, which will be described later.
The one that gives ST (see Figure 2). Reference numeral 11 denotes a switching element control circuit, which is operated by an engine starting signal from a start switch (not shown), etc., and controls the switching element.
Drive signal shown in Figure 2 that controls TR ON/OFF
Causes domestic violence. One cycle of the drive signal DV is a heating period a during which the switching element TR is turned on and the preheating plug is heated.
and a detection period b in which the switching element TR is turned off and the temperature of the preheating plug is detected by a constant current, and if a pulse is given during the heating period a, the switching element TR is turned on. The intermittent cycle is determined from the temperature rise value/time value obtained from the preheating plug temperature-elapsed time characteristic obtained in advance and the allowable range of the set preheating temperature. In this embodiment, it is approximately 15 ms. Also, switching element control circuit 1
1 is the timing pulse that drives the constant current circuit CC
Generates TP. As shown in Fig. 2, the timing pulse TP is generated at the falling edge of the heating period of the drive signal DV, and is generated during the detection period (off period) of the drive signal DV.
A constant current is output from the constant current circuit CC.
12 is a first disconnection detection circuit, which is a differential amplifier.
It includes a memory circuit that stores the voltage value e _t output from AP, and the differential amplifier operates in response to the input pulse SP from the constant current circuit CC during the off period of the intermittent drive signal DV.
The output voltage value e _t of the AP is taken in, and the difference voltage value between it and the voltage value e′ _t of the off-period one cycle before stored in the memory circuit is calculated and output, and the difference voltage value (e _t −e′ _t ) is larger or smaller than a predetermined value e _b . This predetermined value e _b is set to be slightly larger than the temperature change of one intermittent cycle, that is, the voltage value e a, which is determined based on the predetermined preheating plug temperature-elapsed time characteristic, and is set to be slightly larger than the voltage value e _a . If the voltage value changes more than the voltage value change of one intermittent cycle due to the preheating plug temperature-course characteristic, that is, if the differential voltage value | (e _t − e′ _t ) | > e _b , then nothing will happen to the preheating plug GP. This detects when there is an abnormality. Here, the major cause of the abnormal voltage value change mentioned above is the disconnection of the preheating plug GP.
Therefore, by the above comparison, it is possible to detect a disconnection of the preheating plug GP. Reference numeral 13 denotes a second disconnection detection circuit, which detects a disconnection before heating the preheating plug while the first disconnection detection circuit 12 detects the disconnection during heating control of the preheating plug. That is, before the switching element control circuit 11 outputs the first drive pulse, a constant current is caused to flow from the constant current circuit CC, the resulting voltage value e _t is captured at the timing of the capture pulse SP, and the predetermined setting is Voltage value e _c
Compare with. If this set voltage value e _c is set to a voltage value equal to the product of the resistance value r _o of the preheating plug when not preheating and the constant current i, a voltage value e _t that is significantly different from the set voltage value e _c can be compared. When detected, a disconnection output is generated. For example, if four preheating plugs GP, each with a resistance value r, are connected in parallel as shown in the figure,
If all four preheating plugs are not disconnected, the resistance value is r/4, if one is disconnected, it is r/3, if two are disconnected, it is r/2, and three are disconnected. bar
On the other hand, if all the wires are disconnected, the resistance value is ∞
The voltage value when there is no disconnection (i・r/
4) is disconnected (i・r/3,
i·r/2, i·r, 0), this difference is used to detect a disconnection. 14 is a heating control operation latch circuit that latches the first pulse (on period signal) of the drive signal DV of the switching element control circuit 11, holds that heating control has been performed, and uses its holding output to detect the second disconnection. This prohibits the operation of the detection circuit 13. 15 is a latch release circuit which receives a signal from a water temperature sensor (not shown) that detects the water temperature of the radiator, and when the cooling water temperature reaches the preheating plug heating control operating condition (i.e., after starting the engine), it returns to within the heating control operating condition (i.e., after starting the engine). , when the engine is stopped), the heating control operation latch circuit 14 is unlatched, and the second disconnection detection circuit 1 is activated again.
3, disconnection detection is performed. 2 is a disconnection indicator, which is composed of display positions such as lamps and light emitting diodes, and includes first and second disconnection detection circuits 1;
The disconnection detection outputs GPDC1 and GPDC2 of Nos. 2 and 13 are visually displayed and notified to the operator. 16
is a wire breakage number detection circuit, and the difference voltage value |(e _t −e′ _t ) | calculated by the wire breakage detection circuit 12 and the wire breakage detection output
GPDC1 is taken in, the differential voltage value |(e _t −e′ _t ) | is compared with preset comparison voltage values v ₁ , v ₂ ..., the number of disconnections in the preheating plug is detected, and the number of disconnections is determined according to the number of disconnections. The set voltage value e _'s of the set temperature comparison circuit 10 is outputted, and the set voltage value _e's of the set temperature comparison circuit 10 is changed.

Now, the operation of the circuit shown in FIG. 1 will be explained next.

When a starting signal is input from a starter switch (not shown) to the switching element control circuit 11, the switching element control circuit 11 generates a drive signal DV, and the switching element control circuit 11 generates a drive signal DV.
Drives TR on/off (intermittent drive). on the other hand,
Since the switching element control circuit 11 supplies the timing pulse TP generated at the falling edge of the drive signal DV to the constant current circuit CC, a constant current is output from the constant current circuit CC during the off period of the switching element TR.
Therefore, in one intermittent cycle, during the ON period of the switching element TR, the current of the power source E is supplied to the preheating plug GP via the switching element TR, and during the OFF period of the switching element TR, the current of the constant current circuit CC is supplied. will be supplied to the preheating plug GP. The preheating plug GP generates heat due to the current from the power source E, raising the temperature and increasing the resistance value of the preheating plug GP. During the off period of the switching element TR, the voltage value e _t due to the voltage drop of the preheating plug GP is caused by the constant current supplied from the constant current circuit CC.
is output from the differential amplifier AP. The change in the voltage value e _t is proportional to the resistance value change, and therefore the voltage value e _t can be considered as a function of temperature. This voltage value e _t is input to the set temperature comparison circuit 10 and compared with the set voltage value e _s . Through this comparison, if it is detected that e _s > e _t , that is, the preheating plug GP has not reached the set preheating temperature, the switching element is controlled so as to output a pulse that turns on the switching element TR in the next cycle. The circuit 11 is controlled. Conversely, when the preheating plug GP reaches the set preheating temperature,
Since the comparison result is e _t ≧ e _s , a prohibition signal ST that prohibits the output of the pulse that turns on the switching element TR is output to the switching element control circuit 11 in the next cycle.
As shown in Fig. 2, the voltage value e _t during the off period increases as the preheating plug GP is heated by the application of the drive signal DV, and when the set voltage value e _s is reached, the prohibition detected during the off period The signal ST is generated, and the pulse output is prohibited as shown by the dotted line of the drive signal DV in FIG. 2, so the switching element TR is not turned on and no current for heating is applied to the preheating plug GP. During the off period of the next cycle, when it is detected that the temperature of the preheating plug GP is lower than the set preheating temperature (that is, when e _t < e _s is detected as a comparison result), the prohibition signal ST is activated.
is not output, the switching element control circuit 11 emits a pulse indicating the on period in the next cycle.
In this way, the preheating plug GP is heated and controlled up to the scheduled preheating temperature from the time the start signal arrives, and when it reaches the scheduled preheating temperature, it is maintained at this temperature. In this configuration, since a constant current is used for temperature detection, temperature can be detected more accurately than in conventional systems that use current from the power source E. Moreover, since no voltage detection resistor is provided, the This method is particularly effective in cases where there is only a limited power source, such as an engine, without consuming the current for temperature detection.

In the present invention, a disconnection detection circuit 12 and a disconnection number detection circuit 16 are further provided. That is, the disconnection detection circuit 12 operates as a constant current circuit during the off period of the switching element TR.
Acquires the output voltage value e _t of the differential amplifier AP in response to the input pulse SP from CC. And disconnection detection circuit 1
2 outputs the difference voltage from the output voltage value e' _t of the OFF period one cycle before, which is stored in the internal memory circuit.
Since the cycle of the off period is fixed, if the preheating plug GP is not disconnected, the differential voltage value | (e _t −
e′ _t ) | is less than or equal to the voltage difference e _a of one intermittent cycle in the voltage value-elapsed time characteristic determined based on the pre-determined preheating plug temperature-elapsed time characteristic.

Therefore, a set voltage value e _b that is slightly larger than the voltage value e _a is set in the wire breakage detection circuit 12 as a wire breakage detection reference level, and if the differential voltage value |(e _t −e′ _t )| is greater than or equal to e _b , a wire breakage occurs. It is determined that the disconnection detection output is issued, and the differential voltage value |
If (e _t −e′ _t )| is less than or equal to e _b , it is determined that there is no disconnection.
For example, if n preheating plugs, each with a resistance value r, are installed in parallel, if all of them are disconnected, the total resistance value will be ∞, so the differential voltage |(e _t −e′ _t ) | If it is more than e _b and k wires are broken, the total resistance value will be r/(n-k), and the voltage value e _t will be i・r/(n
-k), it is larger than the expected voltage value i・r/n without any disconnection, and the differential voltage |(e _t
−e′ _t )| becomes larger than e _b , making it possible to detect a disconnection. The disconnection detection circuit 12 compares the output of such a voltage difference with a set voltage value during each OFF period, and detects disconnection of the preheating plug GP at an early stage during heating control. The voltage value e′ _t of the previous off-period stored in the memory circuit is an update pulse generated from the switching element control circuit 11 after outputting the differential voltage.
The voltage value e _t of the current off-period is updated and stored by RS, and used to obtain the difference from the voltage value of the next off-period. The disconnection detection output GPDC1 obtained in this way is sent to the disconnection indicator 2, and an indication that there is a disconnection is performed.

This disconnection detection output GPDC1 is also sent to the disconnection number detection circuit 16, and the disconnection number detection circuit 16 receives the differential voltage value |(e _t −e' _t )| from the disconnection detection circuit 12. Here, if the resistance value of each preheating plug during the off period one cycle ago is r′ _t and the resistance value of each preheating plug during the off period of the current cycle is r _t , then one cycle ago, the preheating plug GP
Since not a single wire is broken, the voltage value e′t is e′ _t = i・r′ _t /n (1) On the other hand, during the off period of this cycle, k preheating plugs are broken. Then, the voltage value e _t becomes e _t =i・r _t /(n−k) (2), and the differential voltage value V becomes V=e _t −e′ _t =i・(r _t /n −k−r′ _t /n)(3
) becomes. Here, voltage values V ₁ , V ₂ , V ₃ . . . obtained from equation (3) according to the number k of disconnections are prepared.

V ₁ =i・(r _t /n-1−r′ _t /n) V ₂ =i・(r _t /n−2−r′ _t /n) V ₃ =i・(r _t /n−3 −r′ _t /n) 〓 〓 Then, the difference voltage value V and this prepared comparison voltage value
By comparing V ₁ , V ₂ , V _{3 .} . . , the number k of disconnections can be detected.

In this way, the set temperature voltage value of the set temperature comparison circuit 10 is outputted from the next detected number k of disconnections. Here, the set temperature voltage value e _s that is actually set in the set temperature comparison circuit 10 is: e _s = i・r _s1 /n (4) However, r _s1 is the resistance value of each preheating plug at the scheduled preheating temperature. .

The set temperature and voltage value e′ _s when the k wire is broken is e′ _s = i・r _s1 / (n−k) (5), so depending on the number of broken wires mentioned above, Outputs the specified set temperature and voltage value e′ _s . This voltage value e′ _s
is set or stored as the set temperature voltage value of the set temperature comparison circuit 10. Then, it is used for heating control of the preheating plug GP. FIG. 3 is an explanatory diagram showing changes in the set temperature voltage value and the voltage value of the voltage drop of the preheating plug when a disconnection occurs during heating control. When disconnection of the preheating plug is detected at time t ₁ , the set temperature voltage value of the set temperature comparison circuit 10 is changed from e _s to e′ _s . Furthermore, due to the disconnection, the voltage value e _t of the voltage drop also increases and changes as shown in the figure. Therefore, the voltage value e _t is compared with the set temperature voltage value that changes in this way and the heating is controlled, so that the remaining preheating plugs are accurately controlled to the scheduled preheating temperature.

In the above description, an example has been described in which the control section 1 is configured separately from the comparator circuit 10 to the disconnection number detection circuit 16, but if the control section 1 is configured with a microcomputer, it can be configured with common hardware.
For this purpose, the voltage value e _t is converted into a digital value and inputted to the control unit 1, and the set voltage values e _s , e _b ,
e _c and e _d are stored as digital values in the main memory of the microcomputer, and the arithmetic circuit of the microcomputer calculates the differential voltage value and sets the set voltage value according to a predetermined control program stored in the control program memory. It compares the values and controls the generation of drive signals.

As described above, according to the present invention, a disconnection is detected and the reference voltage value for heating control is changed according to the number of remaining unbroken preheating plugs, so that any one of the preheating plugs is disconnected. Even if the remaining preheating plug is heated up to the scheduled preheating temperature, the remaining preheating plug can be stably controlled to the preheating temperature.
Therefore, it is possible to easily start the engine, etc. using the remaining preheating plug without causing any unexpected situation such as overheating.

Further, according to the present invention, since a constant current is passed from the constant current circuit during the off period of the switching element to detect the voltage value of the voltage drop of the preheating plug and the number of disconnections is detected, the power supply for heating the preheating plug is detected. It has the advantage of being able to detect the number of disconnected wires without consuming energy, and improving its accuracy since it uses a constant current. Furthermore, since the constant current circuit for temperature detection used to control the temperature of the preheating plug is shared, the number of broken wires can be detected by simply capturing the voltage value, and the configuration is not particularly complicated and can be configured at low cost. becomes. Furthermore, the number of disconnected wires is detected by finding the difference between the voltage value of the off-period of the previous cycle and the voltage value of the current off-period, and comparing the difference with a predetermined reference value, so heating control is performed intermittently from the start to the end. As a result, the number of wire breaks can be detected, which is extremely effective in practical terms, such as early detection of wire breaks.

Although the present invention has been explained using one example, the present invention is not limited to the above-mentioned example, and various modifications can be made in accordance with the gist of the present invention, and these are excluded from the scope of the present invention. isn't it.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a waveform diagram of each part of the embodiment of FIG. 1, and FIG. 3 is an explanatory diagram of the operation of the present invention. E...power supply, TR...switching element, GP...preheating plug, CC...constant current circuit, AP...differential amplifier, 1
... Control unit, 2 ... Disconnection indicator, 12, 13 ...
Disconnection detection circuit, 16...Disconnection number detection circuit.

Claims (1)

[Claims] 1. A detection circuit that detects the number of disconnected preheating plugs from the combined resistance value of the preheating plugs connected in parallel, and a control device that reduces the current applied to the preheating plugs in accordance with the number of disconnections of the preheating plugs based on the output of the detection circuit. A preheating plug heating control device having a preheating plug heating control device.