JPS6198971A - Start preheating device of diesel engine - Google Patents

Abstract

PURPOSE:To perform rapid preheating with no load being applied to a glow plug, by connecting a negative temperature resistance element in a preheating circuit, connecting a power supply with the glow plug, so as to allow a small electric current to flow when an engine is started at a low temperature. CONSTITUTION:If a starter switch 2 is closed when an engine is started at a normal temperature, an electric current is allowed to flow in a glow plug 8 through a sensing resistor 3 and a switch 4. And if voltage across both ends of the sensing resistor 3 comes to be in a preset value or less, a controller 6 opens the switch 4 while closes a switch 5. Consequently, an inflow current to the glow plug 8 is decreased by a resistor 7, and the glow plug 8, when it is heated to a temperature in a fixed value or more, is released from rapid heating by the controller 6. The above device connects a negative temperature characteristic element 11 in a circuit connecting the switch 4 with the glow plug 8. And the device decreases resultant resistance at low temperature time as compared with that when the engine is started at the normal temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a preheating device for a diesel engine, and particularly to one using eight glow plugs.

(Prior art) When starting a diesel engine, the compressed air in the combustion chamber is preheated to promote ignition of the fuel spray and improve startability.Today, glow plugs are used as a heat source for preheating. Preheating JA equipment is generally widely used.

Fig. 2 shows a conventional example of such a preheating device. Based on this, switching is performed by a control signal output from the controller 6. Reference numeral 7 indicates a current limiting resistor connected to the switch 5, and 8 indicates a glow plug.

In such a preheating device, when the engine is started at room temperature,
When the starter switch 2 is closed, the TL flow is applied to the glow plug 8 via the sensing resistor 3 and the light source 4. Since this glow plug 8 has a resistance characteristic of +E temperature as shown by the dotted line R in FIG. 3, the resistance value increases as the glow plug 8 ages. Therefore, the current rg flowing into the glow plug 8 is also
It gradually decreases as shown by the curve al in the figure. For this reason, the current flowing through the sensing resistor 3 also decreases, and when the voltage across the sensing resistor 3 falls below a preset threshold, the controller 6 opens the switch 4 and closes the switch 5 based on this voltage. . Therefore, the current flowing into the glow plug 8 is limited by the resistor 7, and the current flowing into the glow plug 8 is limited by the curve a2 in FIG. It decreases significantly as shown at +15. For this reason, when the glow plug 8 is heated to a temperature higher than a certain temperature, the rapid heating of the glow plug 8 by the controller 6 is canceled. By doing so, it is possible to prevent the glow plug from rising in temperature beyond the maximum allowable temperature and being damaged during rapid heating. In other words, such a preheating device is useful for preventing thermal damage to the glow plug 8 when starting the engine in a normal temperature atmosphere.

(Problem to be solved by the invention) However, when the ambient temperature is low such as in winter and there is a coal soak situation when starting the engine, the temperature of the entire engine including the glow plug 8 decreases when the engine is started, and the temperature of the glow plug 8 decreases. Since a voltage is suddenly applied while the resistance value is lower than the rated value, a large current flows into the glow plug 8 due to the above-mentioned positive temperature resistance characteristic of the glow plug 8, and the temperature of the glow plug 8 decreases. There was a problem in that the heater wires, insulating ceramics, etc. were damaged or deteriorated due to heating exceeding the maximum allowable temperature.

The present invention solves this problem by causing a current that is slightly smaller than that in a steady state to flow through the claw plug even when starting the engine at a low temperature, thereby allowing rapid preheating without putting a burden on the glow plug. The purpose of this invention is to provide a starting preheating system for a diesel engine.

(Means for Solving the Problems) The present invention has a configuration in which a negative temperature resistance element is connected to a preheating circuit that connects a power source and a glow plug.

(Function) During call talk, the temperature of the glow plug drops, so the resistance value is small, however.

The resistance value of the negative temperature resistance element is large, and it performs rapid heating while suppressing the current flowing to the glow plug to be slightly smaller than when starting at room temperature. Therefore, it prevents overheating of the glow plug or damage to the heater wire or ceramic due to overheating. to prevent.

(Example): Figure 51 is a circuit diagram of the starter 8 device of the present invention, and the same components as those shown in Figure 2 are given the same reference numerals and the overlapping configurations and functions will be explained. omitted.

That is, the difference between FIG. 2 and FIG. 1 is that a negative temperature characteristic element 11 is connected in an eight-way circuit between the switch 4 and the glow plug 8. This negative temperature characteristic element 11 has characteristics as shown by the solid line R2 in FIG. 2, and exhibits a large resistance value in a low temperature situation. Note that by providing the negative temperature characteristic element 11 close to the glow plug 8, it is possible to detect a temperature closer to the temperature of the glow plug 8.

As a result, the combined resistance of the glow plug 8 and the negative temperature characteristic element 11 at the above-mentioned low temperature is reduced to a slightly smaller value than when starting at a steady temperature, as shown by the chain line R5 in FIG. Note that the controller 6 cancels the rapid preheating at a set voltage threshold level when the resistance of the negative temperature resistance element is slightly large and a slightly small current flows through it. Therefore, during call talk, damage to the glow plug 8 is prevented while rapid preheating is performed using a slightly smaller current.

In addition, since the resistance of the glow plug 8 becomes large after the engine warms up, even if the resistance of the negative temperature resistance pedestal 11 becomes slightly smaller, the combined resistance value will not become much smaller and this will not be a problem in practice. The negative temperature resistance element 11 can be configured to be able to detect the water temperature in the water jacket (effects of the invention).As described above, according to the present invention, when starting the engine after a cold soak in winter, , it is possible to effectively prevent overheating flow from flowing into the globe lug, and the durability and reliability of the glow plug are greatly improved. Further, effects such as the ability to easily and inexpensively realize a system that minutely changes the terminal voltage of the glow plug depending on the outside temperature and the warm-up state of the enodine can be obtained.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of the starting preheating device of the present invention, Fig. 2 is a circuit diagram of a conventional starting preheating device, Fig. 3 is a temperature vs. resistance characteristic diagram of the glow plug and negative temperature resistance element, and Fig. 4 is the glow plug and negative temperature resistance element. FIG. 3 is a current vs. temperature characteristic diagram of the plug. 1...Power supply, 3...Sensing resistance, 4, 5...
Switch, 6... Controller, 7... Current limiting resistor, 8... Glow plug, 11... Negative temperature resistance element 6 Patent applicant Isuzo Jidosha Co., Ltd. Agent Patent attorney Minoru Tsuji 1 Figure 2

Claims (2)

[Claims] (1) A starting preheating device for a diesel engine having a glow plug, characterized in that a negative temperature resistance element is connected in a preheating circuit connecting a power source and the glow plug. (2) A sensing resistor, a rapid heating release switch controlled by a controller based on the voltage output of the sensing resistor, and a current limiting resistor are connected in the preheating circuit connecting the power source and the glow plug. A starting preheating device for a diesel engine according to claim (1).