JPH0465611B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a load drive circuit, such as a linear solenoid (direct-acting electromagnetic drive device) used for hydraulic control in an automobile power steering device. related to those used to drive loads.

<Prior Art> For example, in a power steering control device described in Japanese Patent Application No. 59-169250, the flow rate of steering assist force generating hydraulic oil is variably controlled by a linear solenoid. This type of linear solenoid can vary its operating stroke by controlling its drive current. For example, in an electromagnetic valve driven by a linear solenoid, the opening degree of the valve can be variably controlled by controlling the drive current supplied to the solenoid. In other words, it is possible to obtain mechanical displacement according to the magnitude of the current.

FIG. 3 shows an example of a circuit that drives a load such as a solenoid as described above based on a command voltage Vin etc. given from a control system such as a microcomputer.

The load drive circuit shown in FIG. 3 consists of a power transistor Q2 that is interposed in series between a power source (vehicle battery) VB and a linear solenoid L as a load and controls the drive current I _O of the solenoid L, and a power transistor Q2 that controls the drive current I O of the solenoid L, A current detection resistor R _S interposed in series between the solenoid L, a differential amplifier circuit A2 that detects the divided voltage V _S appearing across the current detection resistor R _S , and this differential amplifier circuit. Comparison circuit that compares the output voltage V _O of A2 with the command voltage Vin
Equipped with CP. The conduction state of the transistor Q2 is feedback-controlled by the comparison output of the comparison circuit CP.

Here, the comparator circuit CP and the differential amplifier circuit A2 are each operated with a single positive power supply Vcc obtained from an on-vehicle battery VB. By operating with a single power supply Vcc in this manner, the circuit configuration around the power supply can be simplified. Instead, the effective voltage range of each of the comparison circuit CP and the differential amplifier circuit A2, the so-called input dynamic range, is the one power supply Vcc.
and the ground potential, and normal operation will not be possible for input voltages that exceed this range.

The above comparison circuit CP and its surrounding parts include an operational amplifier A1, resistors R1, R2, R3, and a capacitor C.
1 and a driver transistor Q1.

Further, the differential amplifier circuit A2 is constituted by an operational amplifier, and a predetermined voltage amplification gain is set by resistors R4, R5, R6, and R7. Furthermore, this drive circuit, battery VB, and solenoid L are removably connected via connection terminals A and B, respectively.

Further, the negative side of the vehicle battery VB and one end of the solenoid L are commonly connected to the ground potential. In this case, the common ground potential is taken from the vehicle body.

By the way, the above-mentioned solenoid has hysteresis in its electro-mechanical conversion characteristics, as shown in FIG. That is, a difference occurs between the mechanical displacement x obtained when the drive current I _O increases and the mechanical displacement x obtained when the drive current I _O decreases.
This difference adversely affects, for example, the operational accuracy of the power steering described above.

According to the present inventors, as a means to eliminate such hysteresis characteristics,
As shown in FIG. 5, it has been found that it is effective to superimpose an alternating current ΔI on the drive current _IO .

Therefore, in order to superimpose this alternating current ΔI,
The AC voltage ΔV is superimposed on the command voltage Vin.

Furthermore, when the AC voltage ΔV is superimposed on the command voltage Vin, the terminal voltage _V1 of the solenoid L greatly swings below the ground potential (GND) due to the self-induction effect of the solenoid L, which causes the differential amplifier circuit A2 to
If a negative voltage exceeding the effective input voltage range, so-called input dynamics range, is input to the terminal, the feedback operation for controlling the drive current will not be performed normally, so two diodes D1 and D2 are provided to connect the terminals. The drop in voltage _V1 is kept at the contact level.

As a result, the voltage V ₃ actually input to the differential amplifier circuit A2 and the drive current I _O supplied to the solenoid L become as shown in FIG. 6, and the input voltage V ₃ exceeds the input dynamics range. There isn't.

<Problems to be Solved by the Invention> However, in conventional load drive circuits, short-circuit failures occur on the output side of the drive circuit, such as when the lead wire on the circuit output side contacts the vehicle body, or when the solenoid itself short-circuits. In this case, there was no means to detect this. Therefore, problems such as overheating of the drive circuit due to overcurrent may occur. Furthermore, even if such a failure detection means is provided,
Simply detecting whether or not the output side voltage of the drive circuit has reached the ground level is not enough to differentiate it from the output side voltage of the drive circuit, which periodically reaches the ground level as shown in Figure 6 under normal conditions. There is a risk of erroneous judgments due to the inability to attach

Therefore, the present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a load drive circuit equipped with short circuit fault detection means that can reliably distinguish short circuit faults from normal operation of the drive circuit and prevent false judgments. do.

<Means for Solving the Problem> Therefore, in the present invention, in a load drive circuit in which the output terminal voltage periodically becomes the ground level during normal operation, a ground short-circuit failure on the output terminal side of the load drive circuit prevents normal operation. The structure includes a short-circuit failure detection means that outputs a failure detection signal only when the short-circuit failure detection signal continues for a period longer than the ground level duration time.

<Function> As a result, even if the output terminal voltage reaches the ground level during normal operation and this voltage value is input to the short-circuit fault detection means, the fault detection signal will not be output from the detection means during that time, and the short-circuit fault will not occur. Therefore, the failure detection signal is not output until the output terminal voltage remains at the ground level for a long period of time. Therefore, it is possible to reliably distinguish between a normal state and a short-circuit failure state, and there is no misjudgment.

<Example> An example of the present invention will be described below based on the drawings.

FIG. 1 shows the load drive circuit of this embodiment. still,
The basic configuration and operation of the circuit shown in FIG. 1 are the same as those of the conventional circuit described above. Therefore, the following explanation will mainly be about the parts that are different from the conventional one, and the explanation about the overlapping parts will be omitted.

In the figure, in this drive circuit, in addition to the conventional configuration, the input side of the short-circuit failure detection circuit 10 is connected to the connection point a between the current detection resistor R _S of the circuit output section and the diode D2. The detection circuit 10 includes a transistor Q3 whose space is connected to the connection point a via a diode D3 and a resistor R8, a Schmitt trigger circuit ST to which the collector output of the transistor Q3 is input, and a Schmitt trigger circuit ST. It consists of an inverter IN that inverts the output of , a resistor R9 and a capacitor C2 that set a predetermined time constant between input and output.

Next, the operation will be explained based on the time chart shown in FIG.

When the voltage _V3 at the connection point a in FIG. 2 is higher than the GND level, the transistor Q3 is turned on and its collector output goes to the "L" level, so the Schmitt trigger circuit ST is not triggered.
The output becomes “L” level and the inverter inputs
Conversely, an "H" level output is generated from the short circuit failure detection circuit 10, and the short circuit failure detection circuit 10 outputs a normal operation signal.
Further, during normal operation, when the voltage _V3 reaches the ground level, the transistor Q3 is turned off. At this time, the collector output level is determined by capacitor C2 based on the time constant of resistor R9 and capacitor C2.
is charged and gradually rises, but during normal operation,
Before reaching the trigger level of the Schmitt trigger circuit ST, the transistor Q3 returns to the ON state and its collector output drops immediately, so the Schmitt trigger circuit ST is not triggered and the output of the inverter IN goes to the "H" level. The short-circuit failure detection circuit 10 continues to output a normal operation signal.

On the other hand, if voltage _V3 drops to the ground level due to a short-circuit failure on the output side of the drive circuit or solenoid L, transistor Q3 is turned off in the same manner as described above.
Then, charging of the capacitor C2 is started. When this charging operation continues for a predetermined period of time exceeding the ground level duration during normal operation, the collector output reaches the trigger level (indicated by V _T in FIG. 2) of the Schmitt trigger circuit ST. This causes the output of the Schmitt trigger circuit ST to go “H”.
level, so the output of inverter IN is “L”
The level is inverted, and the short-circuit failure detection circuit 10 outputs a short-circuit failure detection signal. Then, by outputting such a signal, a warning device such as a lamp or a buzzer may be activated to notify the driver.

In this way, it is possible to distinguish between normal operation and short-circuit failure, and prevent erroneous determination. In addition, if the short circuit is temporary and normal operation is immediately restored, the circuit configuration allows the capacitor C2 to be discharged instantaneously, so that the short circuit failure detection circuit 10 can quickly return to its initial state, further preventing erroneous judgments. You can make it certain.

<Effects of the Invention> As described above, according to the present invention, a failure detection signal is output only when the short-circuit condition on the circuit output side continues for a predetermined time or more, so that the output side voltage does not change even during normal operation. Even if the drive circuit is at ground level, it is possible to distinguish between normal operation and short-circuit failure, and to reliably detect short-circuit failure without making erroneous determinations.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing one embodiment of the load driving circuit according to the present invention, Fig. 2 is a waveform time chart showing the operation of the short circuit fault detection circuit of the same embodiment, and Fig. 3 is a circuit showing the configuration of a conventional example. 4 is an electro-mechanical conversion characteristic diagram of the linear solenoid, FIG. 5 is a preferred drive current waveform diagram of the same solenoid, and FIG. 6 is a waveform time chart on the output side of the load drive circuit. A2...differential amplifier circuit, CP...comparison circuit, L
...Linear solenoid (load), Q1, Q2, Q
3...Transistor, R _S ...Resistor for current detection,
10...Short circuit failure detection circuit, ST...Schmitt trigger circuit, IN...Inverter, R9...
Resistor, C2... capacitor.

Claims (1)

[Claims] 1 In a load drive circuit that is configured to drive and control the load by controlling the current supplied to the load, and in which the output terminal voltage periodically becomes the ground level during normal operation, a ground short circuit on the output terminal side of the load drive circuit 1. A load drive circuit comprising short-circuit failure detection means that outputs a failure detection signal only when a failure continues for longer than the ground level duration time during normal operation.