JPS59107227A - Detector for disconnection of engine temperature detecting thermistor - Google Patents

Abstract

PURPOSE:To discriminate clearly between normalcy and disconnection of an engine temperature detecting thermistor even in case of severe cold, by detecting the disconnection of the thermistor when a prescribed time elapses after the start of an engine. CONSTITUTION:The signal of a connection point A between a fixed resistance RA and a thermistor Rth is inputted to a controller 4 of a fuel jet quantity or the like as well as a timer 1. The timer 1 is turned on when a prescribed time elapses after the input of an engine start signal, and its output is inputted to a comparator 2. The output of the comparator 2 is inputted to a fail safe device 3, and the output of the fail safe device 3 is inputted to the controller 4.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for detecting disconnection of a thermistor for detecting engine temperature.

In internal combustion engines, the engine temperature, generally the cooling water temperature, is detected for various control purposes, and a thermistor is widely used as this detection means. That is, as shown in Fig. 1, the thermistor Rth whose resistance value changes according to changes in the ambient temperature (cooling water temperature) of the thermistor is connected to a fixed resistance RA.
The engine temperature is detected by connecting the two in series and applying a power supply voltage Vo (8V), and detecting the potential at the connection point A between the two, that is, the terminal voltage of the thermistor Rth.

By the way, in such a temperature detection mechanism, if the thermistor Rth is disconnected, normal temperature detection cannot be performed and control based on temperature detection cannot be performed.
C senses the potential at point A that is equal to o and issues an alarm;
Some devices are equipped with a fail-safe device that suppresses abnormal control as much as possible by outputting a fail-safe signal set to an appropriate value instead of the temperature detection signal.

However, as shown in Figure 2, the resistance value of the thermistor Rth changes from 200Ω to 30Ω over the operating temperature range of the internal combustion engine from -30° to 100'C. In this case, the resistance value of the fixed resistor RA is set to Ω, but in this case, in extremely cold weather, the resistance value of the thermistor Rth is extremely large compared to the resistance value of the fixed resistor RA, so the resistance value is set to Ω as shown in Figure 3. In this case, the potential at point A is almost close to the power supply voltage vO, making it difficult to determine that the wire is disconnected, which may result in erroneous determination. Particularly, in those equipped with a fail-safe device, fail-safe control is performed based on erroneous determinations, so that good control may not be possible.

The present invention has been developed in view of these conventional problems, and has a structure and closure that detects a thermistor disconnection after a certain period of time has passed after the lateral start motion and the engine temperature has risen to a certain extent, thereby preventing erroneous determination of disconnection. It is an object of the present invention to provide a disconnection detection device for a thermistor for detecting an engine temperature, which is capable of properly functioning as a fail-safe device.

The present invention will be explained below based on illustrated embodiments.

FIG. 4 shows an embodiment of the present invention, in which a signal at a connection point A between a fixed resistor RA and a thermistor Rth is input to a control device 4 for controlling the fuel injection amount, etc., and is also input to a timer 1. The timer 1 is turned on after a predetermined time after inputting the engine start signal, and its output is input to the comparator 2. The output of the comparator 2 is input to a fail-safe device 3, and the output of the fail-safe device 3 is input to a control device 4.

Next, the operation of this configuration will be explained with reference to the flowchart shown in FIG. When the engine start completion signal is input to timer 1 for the first time (PI), timer 1 is set (
P2). Then, when the start completion signal, which is input at regular intervals after startup, is input a predetermined number of times and the set time Tx is exceeded (
P3. P4), the potential at point A is input to the comparator 2 to detect disconnection of the thermistor Rth (P5, P6). Then, when the potential V at point A is lower than the set voltage Vx, which is close to the power supply voltage VO, it is determined that the thermistor Rth is normal.
The output of comparator 2 is held at XX□ //.

In this case, control values such as the fuel injection amount corresponding to the engine temperature are calculated based on the signal at the connection point A input to the control device 4.

Further, when the thermistor Rth is disconnected and the potential V exceeds Vx, the output of the comparator 2 becomes 61, the fail-safe device 3 is activated, and a fail-safe signal is output to the control device 4 (PI). In this case, the control device 4 calculates the control value based on the failsafe signal (P8,
P9”).

With this configuration, the disconnection of the thermistor Rth is detected after a predetermined period of time has elapsed after the engine has started, and the resistance value of the thermistor Rth has decreased to some extent as the engine temperature has risen. Therefore, when the thermistor Rth is normal, the potential at point A is the same as that of the adiabatic state. This makes it possible to clearly distinguish between the normal state and the adiabatic state of the thermistor Rth.

Therefore, the shift error safe is not performed due to an erroneous determination of disconnection, and it is possible to prevent poor control of the fuel injection amount, etc.

Although this embodiment shows a device equipped with a fail-safe device, it may also be applied to a configuration that simply outputs a monitor signal to issue an alarm when thermal insulation of the thermistor is detected. This prevents wasteful inspection work.

In addition, if the thermistor is normal, there will be a difference between the potential at point A immediately after startup and the potential after the predetermined time has elapsed, so by comparing the two, the engine temperature (cooling water temperature) per unit time can be determined. It is possible to detect the degree of rise in the amount of water in the radiator, thereby indirectly checking the amount of water in the radiator.

As explained above, according to the present invention, the disconnection of the thermistor for detecting the engine temperature is detected after a predetermined period of time has passed after the engine is started, so that it is possible to clearly distinguish between the correct connection of the thermistor and the disconnection even in extremely cold weather. This can reliably prevent erroneous determination of wire breakage and control failures due to fail-safe control associated therewith, and can stabilize control operations based on engine temperature detection.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing a general engine temperature detection device using a thermistor, Figure 2 is a diagram showing the relationship between the ambient temperature and resistance value of the thermistor of the same device, and Figure 3 is a diagram showing the surroundings of the thermistor of the same device. Diagram showing the relationship between temperature and point A potential, 4th
The figure is a circuit diagram showing one embodiment of the present invention, and FIG. 5 is a flow chart showing the operation of the same embodiment. 1...Timer 2...Comparator 3...Fail-safe device 4...Control circuit RA...Fixed resistance Rth...Thermistor patent Applicant: Japan Electronics Co., Ltd. Agent Patent Attorney Tomijio Sasashima Figure 1 Figure 2 Figure 3
c) Figure 4 Figure 5 Do-! 25 1 tiger (

Claims (1)

[Claims] The thermistor is disconnected by comparing the terminal voltage of the thermistor for engine temperature detection with the value of the thermistor during normal operation.
In the device for detecting il, a delay device is provided to output the terminal voltage of the thermistor after a predetermined time has elapsed after the engine is started,
A disconnection detection device for a thermistor for engine temperature detection, characterized in that the disconnection of the thermistor is detected based on the thermistor terminal voltage output from the delay device.