JPH0160674B2 - - 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 in particular to a heating control device for a preheating plug (glow plug) to bring the preheating plug to a predetermined temperature. The present invention relates to a preheating plug heating control device that controls and reaches a predetermined temperature in a short time.

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.

Several methods have been known in the past, such as the one disclosed in Japanese Patent Publication No. 56-54473, in which a switching element is connected between the glow plug and the power supply, and the element is opened and closed by a signal from an oscillation circuit. A device that maintains the plug temperature at a set temperature by passing intermittent current through the plug and changing the opening/closing cycle of the element by increasing the resistance value as the plug temperature rises.
No. 55-112072 discloses a device that controls the preheating time of a glow plug based on the amount of change in power supply voltage, shortens the energization time when the voltage increases, and extends the energization time when the voltage decreases, or JP-A-55-101771. In order to improve the startability of a diesel engine at low temperatures, suppress the generation of black smoke, and prevent the engine from stopping, the glow plug continues to be energized to keep it warm after the engine has started, and the energization time is controlled by the charging time of the capacitor. There is known a device that stops energizing when the cooling water temperature exceeds a certain value and preheats at a higher voltage than during heat retention to shorten the preheating time. Resistance wire is generally used in such preheating plugs,
This resistance wire has a positive temperature coefficient of resistance in order to shorten the preheating time. Then, in order to control the temperature so that the preheating plug does not heat up 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.

In order to detect the resistance value of the preheating plug in such heating control of the preheating plug, a voltage is applied to the preheating plug intermittently, and the resistance value of the preheating plug is detected when the voltage is turned off. Such a method, for example, uses the resistance value of the glow plug and the cooling water temperature to divide the warm-up condition at engine start into cold, normal temperature, high temperature, etc., as disclosed in Japanese Utility Model Application Publication No. 56-159677, and calculates the time for energizing the plug. A device has been disclosed in which the preheating time is changed to a minimum, and the resistance value is determined from the amount of voltage drop across the plug by flowing a constant current. However, such intermittent control has the disadvantage that it takes a long time to reach the predetermined temperature. As the power supply voltage of the battery or the like fluctuates and becomes lower, the time required to reach the expected temperature becomes longer and longer.

In addition, since the preheating plug is heated to a high temperature, there is a risk of the wire breaking. However, a method for detecting the wire breakage of the preheating plug is based on Japanese Utility Model Application Publication No. 54-68039, which divides at least four glow plugs into two sets, and Connect the circuits in parallel so that the plugs can be connected in series or in parallel within each group by switching, connect each group in parallel during preheating, apply power supply voltage to each plug, and connect the groups in series after a set time. If the plug is disconnected when the four plugs form a bridge, a potential difference will be created between the parallel circuits and a lamp will light up. Although disclosed, the glow plug requires a special connection and implementation is limited to some engines. Further, the glow plug immediately after energization is still at a low temperature, so its resistance value is low, and therefore a large current flows through the glow plug. In order to control this large current, so-called rush current, immediately after energization with a semiconductor switching element, a large-capacity semiconductor switching element is required.
Since large-capacity semiconductor switching elements are expensive, there is a problem in that the entire device becomes expensive.

Therefore, an object of the present invention is to provide an inexpensive preheating plug heating control device that can reach a predetermined temperature in a short time, can control the temperature without being affected by fluctuations in power supply voltage, and is capable of controlling the temperature without being affected by fluctuations in power supply voltage. It is in.

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

In the present invention, since there is no need for temperature detection from the start of heating control of the preheating plug until the time when the temperature reaches near the scheduled temperature, heating is controlled without providing a temperature detection period, and when the preheating plug is near the scheduled temperature, the heating control period is and a temperature detection period are provided alternately to control the temperature of the preheating plug to a predetermined temperature.

Next, examples of the present invention will be described.

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. TR is an electrical switch element made of a semiconductor such as a power transistor. The switch element TR causes a current from the power source E to flow through the preheating plug GP during its on period, and stops supplying the current during its off period, under the control of the control section 1, which will be described later. GP is a preheating plug (glow plug), and there are as many preheating plugs as there are cylinders in the engine, and in Fig. 1 there are four preheating plugs. 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 the timing pulse TP from the control section 1.
A constant current i is passed through the preheating plug GP during the off period of the switch 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 R ₁ and R ₂ . 10 is a set temperature comparison circuit, which determines the desired set preheating temperature (for example, 900°C)
The voltage value e _s (= i × r _s ) determined by the resistance value r _s of the preheating plug GP in is set or stored, and the voltage value e _t during the off period and the set voltage value e output by the differential amplifier AP _s , and when e _t ≧ e _s, a prohibition signal ST (see FIG. 2) is provided to the switch element control circuit 11 (described later). Reference numeral 11 denotes a switch element control circuit, which is operated by an engine starting signal from a start switch (not shown) or the like, and controls the ON/OFF state of the switch element TR after the operation of the relay control circuit 14 (described later) is completed. Generate signal DV. One period of the drive signal DV is the switch element TR
The heating period a consists of a heating period a in which the switch element TR is turned on to heat the preheating plug, and a detection period b in which the switch element TR is turned off and the temperature of the preheating plug is detected by a constant current.
If a pulse is given to , switch element TR turns 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. Further, the switch element control circuit 11 generates a timing pulse TR that drives the constant current circuit CC. 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 causes the constant current circuit CC to output a constant current during the detection period (off period) of the drive signal DV. 12 is a disconnection detection circuit. When the switch element control circuit 11 receives the start signal, it generates a timing pulse TP, and this timing pulse TP causes the constant current circuit CC to flow a constant current. The disconnection detection circuit 12 takes in the voltage value e _t due to the constant current and compares it with a predetermined set voltage value e _c to detect a disconnection of the glow plug.

That is, if the 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 larger than the set voltage value e _c before preheating is set. When _t is detected by comparison, a disconnection output is generated and output to the relay control circuit 14.
That is, assuming that the preheating plugs GP are connected in parallel as shown in the figure, the resistance value of each preheating plug connected in parallel is r,
If the number of parallel wires is n, and the number of disconnected wires is k, the measured voltage value e _t is expressed as e _t =i·r/(nk). Therefore, if the voltage value (i・r/n) when no wire is broken is the set voltage value e _c , if there is a wire break, e _t > e _c , so the wire breakage can be detected by comparison. becomes possible. 13 is a time width setting circuit which receives the voltage value V _p of the power source E applied to the preheating plug GP and outputs a time width signal according to the voltage value. RL is a relay switch such as an electromagnetic relay, 14 is a relay control circuit that controls the operation of the relay switch RL, and a time width setting circuit 13 is activated by a start signal from the switch element control circuit 11.
It outputs a relay operation signal PS with a time width specified by the time width signal, and operates (closes) the relay switch RL.

Now, the operation of the circuit shown in FIG. 1 will be explained in conjunction with the waveform diagram shown in FIG. 2.

When the start signal arrives at the switch element control circuit 11, a timing pulse TP is sent to the constant current circuit CC, and before heating control, a constant current is passed from the constant current circuit CC to the preheating plug GP, and the voltage value due to the voltage drop of the preheating plug GP is Output e _t from the differential amplifier AP.

Then, the disconnection detection circuit 12 takes in this voltage value e _t and compares it with an internally set set voltage value e _c . If e _t > e _c , a disconnection output is sent to the relay control circuit 14, and output of the relay drive signal PS is prohibited. This disconnection output causes a display circuit (not shown) to display a disconnection. On the other hand, if e _t ≦e _c , no disconnection output occurs, so the relay control circuit 14 generates the relay operation signal PS in response to the activation signal of the switch element control circuit 11. This closes the relay switch RL, so the preheating valve GP is connected to the power supply E.
A current is supplied to heat the preheating plug GP.
When the operation signal PS is generated, the operation of the disconnection detection circuit 12 is prohibited. When a current flows from the power supply E to the preheating plug GP, the voltage V _p of the power supply E is applied to the end of the preheating plug GP.
is generated and input to the time width setting circuit 13. The time width setting circuit 13 outputs a time width _tp according to the voltage value _Vp . This time width t _p is determined by creating a preheating temperature _vs. elapsed time characteristic that assumes that when a reference voltage value V _r is applied for a reference time t r, the preheating temperature will reach the preheating temperature after t _r time. The time width t _p is changed according to the difference from _r . That is, the time width t _p is determined by t _p =t _r −k(V _p −V _r ). Note that k is a proportionality constant. Therefore, when the power supply voltage V _p is higher than the reference voltage value V _r , the time width t _p is smaller than the scheduled time t _r , and conversely, V _p <
If V _r , t _p > t _r . Time width setting circuit 13
The time width output _tp is set in the register of the relay control circuit 14, and compared with the value of a counter that counts clocks from the arrival of the activation signal in a comparator circuit, and when they match, the pulse of the operation signal PS is lowered. Therefore,
As shown in FIG. 2, a pulse having a time width t _p determined by the power supply voltage V _p is outputted as an operation signal from the time the activation signal arrives, and the relay switch RL continues to close during this period. Therefore, even if the power supply voltage V _p fluctuates,
By closing the relay switch RL, the preheating plug GP reaches a temperature close to the scheduled preheating temperature. The comparison match output of the relay control circuit 14 is sent to the switch element control circuit 11 and used to trigger the generation of the drive signal DV. The switch element control circuit 11 detects the end of the relay control period based on this coincidence output, generates a drive signal DV, and turns on/off the switch element TR.
Drive off (intermittent drive). On the other hand, since the timing pulse TP generated at the falling edge of the drive signal DV is given from the switch element control circuit 11 to the constant current circuit CC, a constant current is output from the constant current circuit CC during the off period of the switch element TR. Ru. Therefore, in one intermittent period, the current of the power source E flows through the switch element TR during the ON period of the switch element TR.
is supplied to the preheating plug GP via the switch element TR
During the off period of the constant current circuit CC, the current of the preheating valve is
It will be supplied to 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 switch element TR, the voltage value e _t due to the voltage drop across the preheating plug GP is output from the differential amplifier AP by the constant current supplied from the constant current circuit CC.
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 _es . By this comparison, e _s >
e _t , that is, when it is detected that the preheating plug GP has not reached the set preheating temperature, the switch element is activated in the next cycle.
The switch element control circuit 11 is controlled to output a pulse that turns on the TR. Conversely, when the preheating plug GP reaches the set preheating temperature, the comparison result is e _t ≧ e _s , so in the next cycle, the prohibition signal ST that prohibits the output of the pulse that turns on the switch element TR is sent to the switch element. It is output to the control circuit 11. As shown in Fig. 2, the voltage value e _t during the off period increases due to the heating of the preheating plug GP due to the application of the drive signal DV, and when it is detected during the off period that it has reached the set voltage value e _s . Generates the prohibition signal ST and drives the drive signal DV in Figure 2.
As shown by the dotted line, the pulse output is prohibited, so the switch element TR is not turned on, and no current for heating is applied to the preheating plug GP. In the off period of the next cycle, if it is detected that the temperature of the preheating plug GP is below the set preheating temperature (that is, if e _t < e _s is detected as a comparison result), the prohibition signal ST will not be output. , the switch element control circuit 11 outputs a pulse indicating the on period in the next cycle. In this way, the preheating plug GP is intermittently controlled to be heated up to the scheduled preheating temperature after the end of the relay control period, and furthermore, when it reaches the scheduled preheating temperature, it is maintained at this temperature. Since this kind of intermittent control uses a constant current for temperature detection, it is possible to accurately detect temperature without being affected by fluctuations in the power supply voltage, compared to conventional methods that use current from power supply E. Since no resistor is provided, the current of the power source E is not consumed for temperature detection, which is particularly effective when the engine has only a limited power source.

In the above description, an example has been described in which the control section 1 is divided into five component circuits, ie, the set temperature detection circuit 10 to the relay control circuit 14, but if a microcomputer is used in the control section 1, these circuits can be made common.
For this purpose, the voltage values e _t and V _p are input into the microcomputer as digital values, and the set voltage values e _c , e _s , V _r , and time width t _r are stored in its memory, and the microcomputer inputs them into the microcomputer. Comparison of voltages, calculation of time width, and generation of pulses (drive signals) may be performed according to the control program of the memory.

As described above, according to the present invention, the relay switch heats the preheating plug by continuously passing an electric current until it reaches a predetermined temperature, and then controls the semiconductor switch intermittently, detects the temperature, and heats the preheating plug. Since the temperature of the preheating plug is maintained at the scheduled temperature, the time required for the preheating plug to reach the scheduled temperature is shortened, and the period when the preheating plug is not heated can be used to detect the temperature of the preheating plug, allowing for accurate and detailed temperature detection. The present invention can be provided at a low price because the semiconductor switch has a small capacity.

Furthermore, in the present invention, since the temperature is detected by flowing a constant current during the off period of the switch element and detecting the voltage value of the voltage drop of the preheating plug, the power consumption for heating the preheating plug is reduced. It has the advantage of being able to detect temperature and improving its accuracy since it uses constant current.

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, and FIG. 2 is a waveform diagram of each part of the embodiment of FIG. E...Power supply, TR...Switch element, GP...
Preheating plug, CC... constant current circuit, AP... differential amplifier, 1... control section, 10... set temperature comparison circuit,
11...Switch element control circuit, 14...Relay control circuit, RL...Relay switch.

Claims (1)

[Scope of Claims] 1. A preheating plug heating control device that heats a preheating plug to a set temperature by intermittent energization by an opening/closing element, and measures the temperature of the preheating plug based on a voltage drop due to a constant current when energization is interrupted, wherein the opening/closing element is composed of a first switching element having a mechanical contact that conducts the rush current when the power is turned on, and a current smaller than the current after the rush current passes in parallel with the first switching element. A preheating plug heating control device characterized in that a second switching element made of a semiconductor element that controls disconnection is connected. 2. The preheating plug heating control device according to claim 1, wherein the operating time of the first switching element is determined by measuring the voltage supplied to the preheating plug from the power source. 3 The operation of the first switching element is performed when the voltage value of the preheating plug generated by the constant current flowed from the constant current circuit before the operation of the first switching element is larger than the set voltage value. The preheating plug heating control device according to claim 1 or 2, wherein the preheating plug heating control device is prohibited.