JPH0228711B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a temperature control device for a glow plug that preheats gas in an alcohol engine, a diesel engine, or the like.

Generally, in alcohol engines, diesel engines, etc., the fuel is ignited by the heat of compression of the gas, but in cold weather there is a lot of heat loss, so it is difficult to ignite the fuel with just the heat of compression, making it difficult to start. Therefore, a glow plug is used to preheat the gas. Therefore, in the case where the gas is preheated by the glow plug, the temperature is controlled after the temperature of the glow plug rises to effectively preheat the gas and to prevent the glow plug itself from fusing due to high temperature. It is necessary to do so.

Conventionally, as a temperature control device for this kind of glow plug, in a glow plug whose heating coil material has a positive temperature coefficient, its resistance value changes linearly according to the glow plug temperature, as shown in Figure 1. Utilizing this characteristic, we detect the resistance value of the glow plug when it is energized and control the energization by comparing it with a reference value so that it is always kept constant (for example, the resistance value when the glow plug reaches 900℃). I'm trying to get them to do it. That is, as shown in Figure 2,
A bridge circuit is formed by connecting a reference resistor R1 and a glow plug GP in series through a relay contact RL/a in the power supply circuit of battery B, and providing resistors R2 and R3 in parallel. While comparing the potential at each voltage dividing point by
When the temperature of the glow plug GP is low and its resistance value is smaller than that of the reference resistor R1, the comparator
Activate relay RL with CMP's high level output,
Furthermore, when the temperature of the glow plug GP is high and its resistance value is greater than that of the reference resistor R1, the output of the comparator CMP becomes a low level, and the energization control of the glow plug GP is performed to deenergize the relay RL. By doing this, the bridge circuit is balanced, and the relay RL is temporarily energized again by the pulse signal emitted from the pulse generator circuit PG after a certain period of time (for example, 3 seconds) after the power is cut off due to the deenergization of the relay RL. The bridge circuit is configured so that it can be detected whether or not it is in a balanced state, and the energization control of the glow plug GP can be repeatedly performed. However, with this configuration, as shown in Figure 3, the initial relay
After the glow plug GP is energized by turning on RL and its temperature reaches the standard value S (900℃),
A certain period of de-energization T after relay RL is turned off
(3 seconds) later, energization control is performed such that relay RL is forcibly turned on to maintain the temperature of glow plug GP at reference value S.

However, conventional methods perform temperature control to prevent the temperature of the glow plug GP from exceeding a certain value by detecting the temperature of the glow plug GP and keeping it at a constant value when the glow plug GP is energized. In the glow plug temperature control device, if fuel adheres to the glow plug GP during the non-energization period T of the glow plug GP, its temperature will drop rapidly and greatly (see section A in Figure 3). Therefore, when the power is turned on after the T period, the glow plug
There is a problem in that it takes time for the temperature of the GP to rise to the reference value S, and the energization time during that time becomes long (see section B in the figure), resulting in poor responsiveness of constant temperature control.

The present invention has been made with these points in mind, and by controlling the temperature of the glow plug so that it does not fall below a certain value, fuel will adhere to the glow plug and its temperature will drop rapidly. To provide a temperature control device for a glow plug, which is capable of suppressing the temperature drop as much as possible, quickly rising to a reference temperature, and performing constant temperature control with good responsiveness of the glow plug. be.

In the glow plug temperature control device according to the present invention, a glow plug is provided in one branch of the bridge circuit, and a change in resistance value according to the temperature is detected by comparing it with a reference value, and the glow plug is connected to the bridge circuit according to the detected output. When controlling the opening and closing of the glow plug's energizing relay to balance the circuit, it is possible to control the temperature at a constant level by detecting changes in the glow plug's resistance value when the glow plug is not energized. This makes it possible to quickly respond to a sudden drop in temperature of the glow plug.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the accompanying drawings.

In the glow plug temperature control device according to the present invention, as shown in FIG. 4, the bridge circuit BRG is directly connected to the battery B and is provided with a glow plug GP having a positive temperature coefficient in one branch.
and the reference resistance R in the bridge circuit BRG.
A relay contact RL・a is provided in parallel with 1, and the relay RL injects battery B into the glow plug GP via the relay contact RL・a when energized, and the reference resistor R1 in the bridge circuit BRG and the glow plug GP. a comparator CMP that compares each potential at the voltage dividing point of and the voltage dividing point of resistors R2 and R3;
A flip-flop FF is reset through a delay circuit DLY1 in accordance with the comparison output, and energizes the relay RL by a negative signal of the set Q output; Delay circuit DLY
2, and a timer TM for setting the flip-flop FF through FF.

The operation of the glow plug temperature control device according to the present invention configured as described above will be explained below with reference to the control characteristic diagram shown in FIG.

First, when battery B is input to the bridge circuit BRG at an early stage (relay RL is de-energized), the temperature of the globe lag GP is very low and its resistance value is small.
The output of CMP becomes high level, which resets the flip-flop FF and relays it.
RL is energized, its relay contact RL・a closes, and the glow plug GP starts to be energized. In addition,
Glow plug GP while relay RL is energized
The output of the comparator CMP will be at a high level regardless of the temperature state. At the same time, flip-flop
By resetting FF, timer TM becomes operational (setting Q of flip-flop FF).
The timer TM then sets the flip-flop FF after a certain period of time t (e.g. 2 to 3 seconds), de-energizes the relay RL and energizes the glow plug GP. make it sever. At this time, the flip-flop
The timer TM is reset by the set Q output of the FF becoming high level. Next, the temperature of the glow plug GP is detected again in the bridge circuit BRG, but since the temperature of the glow plug GP has not yet reached the reference value, the output of the comparator CMP becomes high level, and as in the previous case, the temperature of the glow plug GP is detected again. The glow plug is activated only during the predetermined time period t of the timer TM.
Power is applied to the GP. By repeating this operation, the temperature of the glow plug GP is raised to near the reference value S (for example, 900° C.). Note that the characteristics during the period indicated by T _D in FIG. 5 indicate the operating state of the glow plug GP until its temperature rises.

Next, when the temperature of the glow plug GP rises to the point where it exceeds the reference value S, the bridge circuit
The temperature of the glow plug GP in BRG is detected, but the problem is that the temperature of the glow plug GP is high and its resistance value is larger than the reference resistance value R1.
The output of CMP maintains a low level state and does not change the state of flip-flop FF in any way, but as time passes and the temperature of glow plug GP decreases to the reference temperature S, the output of comparator CMP becomes high level. Flip Flop
FF is reset, thereby energizing relay RL and timer TM working for a certain period of time t.
Only the glow plug GP is energized. Thereafter, similar control operations are repeated so that the lower limit of the temperature of the glow plug GP is always maintained at a constant value.

Therefore, in the glow plug temperature control device according to the present invention configured as described above, even if fuel adheres to the glow plug GP during de-energization and its temperature drops rapidly, the temperature control device When the temperature reaches the reference temperature S, the glow plug GP is energized for a certain period of time t.
The temperature of the GP will be restored immediately (5th
(See part C in the figure).

Note that the delay circuits DLY1 and DLY2 are both provided to stabilize circuit operation.

FIG. 6 shows another embodiment of the present invention, in which a constant current circuit CC and a diode D are provided in place of the reference resistor R1 in the bridge circuit BRG, and a Zener diode is provided in the resistor circuit. A more stable glow plug GP with a ZD to ensure constant voltage.
temperature detection.

As described above, the glow plug temperature control device according to the present invention detects the bridge circuit in which a glow plug is provided in one branch and is directly connected to a DC power supply, and the bridge circuit, and detects the equilibrium state of the bridge circuit, and A comparator that produces a high-level output when the resistance value of the plug becomes smaller than a reference value, a flip-flop that is reset by the high-level output of the comparator, and a flip-flop that is energized according to the output when the flip-flop is reset. A relay that applies DC power to the glow plug through its operating contact when energized, and a timer that becomes active in response to the output of the flip-flop when it is reset and sets the flip-flop at a fixed time. Unlike conventional glow plugs, the temperature is controlled so that the temperature of the glow plug does not fall below a certain value, so there is no possibility that fuel may adhere to the glow plug and cause its temperature to drop suddenly. Even if there is a temperature drop, the temperature drop can be suppressed as much as possible and the temperature can be recovered quickly, instead of the conventional method where the temperature drop becomes large and takes time to recover.
It has the excellent advantage of being able to perform constant temperature control of the glow plug with good responsiveness. Furthermore, in the present invention, since the glow plug is energized independently of the bridge circuit, the glow plug can be energized without causing loss due to the reference resistance in the bridge circuit as in the conventional case. It also has the advantage of being able to

[Brief explanation of drawings]

Fig. 1 is a diagram showing the temperature resistance characteristics of a general glow plug, Fig. 2 is an electrical wiring diagram showing a conventional glow plug temperature control device, Fig. 3 is a characteristic diagram showing its temperature control state, Fig. 4 is an electrical wiring diagram showing one embodiment of the glow plug temperature control device according to the present invention, Fig. 5 is a characteristic diagram showing the temperature control state in the same embodiment, and Fig. 6 is another embodiment of the present invention. FIG. B...Battery, GP...Glow plug, BRG
... Bridge circuit, RL ... Relay, CMP ... Comparator, FF ... Flip-flop, TM ... Timer, DLY1, DLY2 ... Delay circuit, CC ... Constant current circuit.

Claims (1)

[Claims] 1 Detects the equilibrium state of a bridge circuit in which a glow plug is installed in one branch and is directly connected to a DC power supply, and the glow plug goes high when the resistance value of the glow plug becomes smaller than the reference value. A comparator that produces a level output, a flip-flop that is reset by the high-level output of the comparator, and a flip-flop that is energized according to the output of the flip-flop at the time of reset, and a direct current is applied to the glow plug through the operating contact when the flip-flop is energized. A glow plug temperature control device comprising a relay that turns on power, and a timer that becomes operational in response to the output of the flip-flop when it is reset and sets the flip-flop after a certain period of time.