JPH1130639A - Leak detector of inductance load driving circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a leak detector that is able to detect such a fact that a leakage current of a drive circuit driving the load of inductance increases beyond the threshold value, so accurately through a simple circuit structure. SOLUTION: This detector is equipped with a diagnosing pulse signal generating means 11 generating a rectangular wave-form diagnosing pulse signal being fed to a drive circuit 2 as a driving input signal and a level judging means 12 judging of whether a reverse voltage being generated immediately after in an output terminal 2a of the drive circuit 2 to be connected to an inductance load 1, at a point of falling time of the diagnosing pulse signal, is less than a threshold voltage level or not, respectively. Pulse duration of the diagnosing pulse signal is within the time range making a load current increasable attending upon the time elapse from the point of rising-up time of the diagnosing pulse signal, and it is set up so as to generate the reverse voltage of the threshold voltage level to the tolerance limit value of equivalent leak resistance seen at the output terminal 2a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a leak detecting circuit for an inductance load driving circuit for detecting that a current leak of a driving circuit for driving an inductance load increases beyond a threshold value.

[0002]

2. Description of the Related Art In FIG. 4, a driving circuit 2 has an FET Q1 as a driving output element which has an inductance load 1 such as a solenoid valve having one terminal connected to a + B power supply and the other terminal connected to an output terminal 2a. Drives in response to a drive input signal. In order to detect an increase in current leak due to an abnormality of a circuit element including the FET Q1, the drive circuit 2 includes a power supply voltage dividing circuit 3 using a series resistor, a voltage dividing circuit 4 for an output terminal 2a, and a The circuit includes a comparator 6 for detecting a voltage difference between the divided voltages, an inverter 7 for inverting the divided voltage of the voltage dividing circuit 4, a CPU 8, and an overvoltage preventing diode 5 for preventing the application of positive and negative overvoltages to these circuits. A leak detection circuit is included. The difference voltage between the divided voltages of the two voltage dividing circuits 3 and 4 is the divided voltage between the internal resistance of the inductance load 1 and the equivalent leak resistance _RL seen at the output terminal 2a which decreases with the increase of the leak current. , The CPU 8 detects such a difference voltage between the DC divided voltages and determines whether or not the equivalent leak resistance _RL falls below the allowable limit value. Further, the CPU 8 takes in the inversion voltage of the inverter 7 and causes a step-like voltage drop to occur at the output terminal 2a when the rectangular pulse-shaped diagnostic pulse signal is input to the drive circuit 2 at the rising time. The disconnection or short circuit of the inductance load 1 is detected by determining whether or not the on / off of the voltage drop that returns to the step shape has occurred.

[0003]

However, in the case of such a leak detection circuit, it is impossible to perform high-precision detection unless the accuracy of both voltage dividing circuits is increased, and the power supply is not supplied to the same equivalent leak resistance. There is also a problem that the divided voltage fluctuates due to the fluctuation of the voltage. Further, it is necessary to detect a difference voltage separately from a circuit for detecting an on / off voltage.

In view of the foregoing, the present invention provides an inductance load driving circuit capable of detecting, with a simple circuit configuration, an increase in leakage current of a driving circuit for driving an inductance load exceeding a threshold value with high accuracy. An object of the present invention is to provide a leak detection circuit.

[0005]

In order to achieve this object, according to the present invention, according to the present invention, a leak detection of an inductance load drive circuit for detecting an increase in current leak of a drive circuit for driving an inductance load is provided. In the circuit, a diagnostic pulse signal generating means for generating a rectangular waveform diagnostic pulse signal supplied as a drive input signal to the drive circuit, and a falling point of the diagnostic pulse signal at an output terminal of the drive circuit connected to the inductance load Level determining means for determining whether or not a reverse voltage generated immediately after the diagnostic pulse signal falls below the threshold voltage level, and the pulse width of the diagnostic pulse signal is increased with the passage of time from the rise of the diagnostic pulse signal. The reverse voltage of the threshold voltage level occurs within the time range where the current can be increased and the allowable limit value of the equivalent leakage resistance seen at the output terminal. Characterized in that it is set to so that.

A load current corresponding to the pulse width of the rectangular pulse-shaped diagnostic pulse signal flows through the inductance load, and releases the energy stored in the inductance load immediately after the end point of the diagnostic pulse signal, that is, immediately after the rising point. And
At this time, a spike-shaped reverse voltage in the direction opposite to the voltage drop is generated at the output terminal. The reverse voltage level and its attenuation waveform change depending on the inductance of the inductance load and its internal resistance, but depending on the value, the reverse voltage level is also reduced as the equivalent leak resistance becomes smaller and the equivalent leak resistance becomes smaller. Become. The level determining means determines whether the reverse voltage is lower than the threshold voltage level and detects an abnormal increase in the leak current.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A leak detecting circuit of an inductance load driving circuit according to an embodiment of the present invention will be described with reference to FIGS. The drive circuit 2 has the same configuration as the conventional circuit described with reference to FIG.
A resistor R1, which constitutes a voltage dividing circuit for dividing the output voltage,
A leak detection circuit 10 including a microcomputer including a CPU, a ROM, a RAM, and the like is connected through R2 and overvoltage protection diodes D1 and D2 that prevent overvoltage in both positive and negative directions. The series resistance value of the resistors R1 and R2 is set to be sufficiently larger than the equivalent leak resistance R _L seen at the output terminal 2a which is assumed to correspond to the leak current regarded as abnormal, and the input resistance of the leak detection circuit 10 is also sufficiently large. Is set.

The leak detection circuit 10 generates a rectangular waveform diagnostic pulse signal to be supplied to the drive circuit 2 by the CPU executing the diagnostic program stored in the ROM in cooperation with the RAM or the like. Pulse signal generating means 11
When, the level determining means 12 connected to the output terminal 2a to be connected to the inductive load 1, and the reverse voltage V _B generated immediately after the falling time of diagnosis pulse signal determines whether Shitamawaru the threshold voltage level And an on / off judging means 13 for judging whether or not the voltage of the output terminal 2a drops at the time of the rise of the diagnostic pulse signal and on / off of the voltage drop that returns at the time of the fall has occurred. It is configured.

That is, the diagnostic pulse signal generating means 11
As shown in FIG. 2, for example, the counter 11 of the CPU responds to a diagnosis command signal supplied when the operation of the drive circuit 2 starts.
is reset to turn on the output port, a preset value corresponding to the pulse width to be output is loaded into the comparison register 12b, and when the count value of the counter 11a reaches the preset value, a coincidence signal is generated and turned off. As a result, a rectangular pulse signal having a predetermined width is generated.

[0010] the inductive load 1, when driven for switching with a pulse signal of a rectangular wave, mainly its inductance L _B and the load current I _L increases substantially linearly defined time constant at its internal resistance to flow , Energy L _B stored in inductance load 1 at the time of falling
Emits I _L ² , thereby producing a reverse voltage V _B at the output terminal 2a. That level is normally defined by the main inductance L _B and its internal resistance, the equivalent leakage resistance R _L begins to affect the smaller. Thus, the diagnostic pulse signal P _D of the rectangular wave is set to a pulse width defining a load current I _L for generating a threshold voltage level for to be determined as abnormal leakage resistor R _L. In other words, this pulse width is
Such is set within a time range that can increase the load current I _L over time from the rise time of diagnosis pulse signal to allow for setting.

[0011] Level determination unit 12, A / D conversion port time including the time-domain reverse voltage V _B from the input immediately before the diagnosis pulse signals in the work area of the RAM is generated through the width T
(See FIG. 3) captures a voltage signal, + level detecting from B Power supply voltage to the corresponding steady-state level to the peak value of the spike voltage waveform corresponding to the reverse voltage V _B, or not Shitamawara the threshold voltage level Determine whether or not.

The on / off judging means 13 analyzes the voltage waveform data taken into the work area of the same RAM, and turns on the step-like voltage drop V _S at the rise of the diagnostic pulse signal and turns off at the fall. It is determined whether or not.

The operation of the leak detection circuit thus configured is as follows. When the diagnostic command signal is input, a rectangular-wave diagnostic pulse signal is input to the drive circuit 2 in place of the normal drive input signal, and the inductance load 1 is switched. Load current I _L, by gradually rises substantially linearly from the rise time of diagnosis pulse signal P _D, a current accumulated from the falling time of the pulse signal is suddenly terminated to the inductive load 1 is discharged , Reverse voltage V _B
Occurs. When the leak current increases due to the abnormality of the drive circuit 2 and the equivalent leak resistance _RL decreases to an allowable limit, the reverse voltage V _B increases from the level corresponding to the power supply voltage.
Reaches the threshold voltage level, and an abnormality is notified. At the same time, step-like voltage drop V _S corresponding to the pulse width at the input of the diagnostic pulse signal when not turned on / off, as well as the inductive load 1 abnormality is notified.

[0014]

According to the first aspect of the present invention, a simple circuit configuration for detecting an abnormal leak due to a reduction in the level of the back electromotive voltage of the drive output of the inductance load, and detecting a relative level with respect to the power supply voltage level to achieve a high level. Accurate leak detection becomes possible. The influence of a relative error in detecting the difference voltage between the two conventional voltage dividing circuits is also avoided. According to the second aspect of the present invention, the disconnection and short circuit of the inductance can be detected with a simple circuit configuration by sharing the rectangular wave pulse signal for leak detection.

[Brief description of the drawings]

FIG. 1 is a diagram showing a circuit configuration of a leak detection circuit of an inductance load drive circuit according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a diagnostic pulse signal generating means of the leak detection circuit.

FIG. 3 is a diagram illustrating the operation of the leak detection circuit.

FIG. 4 is a diagram showing a configuration of a leak detection circuit of a conventional inductance load driving circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Inductance load 2 Drive circuit 10 Leak detection circuit

Claims (2)

[Claims] 1. A leak detection circuit for an inductance load drive circuit for detecting an increase in current leak of a drive circuit for driving an inductance load, wherein a rectangular wave-shaped diagnostic pulse signal supplied as a drive input signal to the drive circuit is provided. Means for generating a diagnostic pulse signal, and determining whether a reverse voltage generated immediately after the falling point of the diagnostic pulse signal at the output terminal of the drive circuit connected to the inductance load falls below a threshold voltage level. A pulse width of the diagnostic pulse signal is within a time range in which a load current can be increased with a lapse of time from a rising point of the diagnostic pulse signal, and the pulse width of the pulse signal is determined by an output terminal. Characterized in that a reverse voltage of the threshold voltage level is generated with respect to the allowable limit value of the equivalent leak resistance. Leak detection circuit inductance load drive circuit. 2. An on / off judging means for judging whether or not a voltage drop at an output terminal at the rise of a diagnostic pulse signal and on / off of a voltage drop to be restored at a fall has occurred. The leak detection circuit for an inductance load drive circuit according to claim 1, wherein: