JPH02162159A - Electric power steering device - Google Patents

Abstract

PURPOSE:To detect a short circuit of a steering motor and prevent a trouble resulting from it by detecting whether the current flowing through the steering motor is within a preset range. CONSTITUTION:When a steering motor 6 is broken or a motor wiring is short- circuited, a large current flows through the steering motor 6 in response to the pulse drive signal as shown after the time t2, and a square wave-shaped current output changed at a large level in response to the drive pulse is obtained from a differential amplifier 20. It deviates from the range of threshold values Vref1 and Vref2 of a window comparator 21, thus an L-level output is obtained from the window comparator 21, a flip-flop 25 is set via a gate circuit 23, gates of gate circuits 18a and 18b are closed by the Q bar output, no pulse signal is fed to FET 15 and 16 from a lower FET drive section 12, and the drive of a switching element is stopped.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to an electric power steering device for driving a steering wheel of a vehicle by a steering motor.

[Conventional technology]

As shown in Japanese Patent Application Laid-Open No. 59-156863, a conventional electric power steering motor drive device has a first motor drive device that is electrically connected when steering in the left and right directions. 2nd and 3rd. A bridge connection is made around the steering motor using a control element such as a fourth transistor. When steering to the right, the first control is performed based on the detection of the steering torque. The second control element is made conductive at the same time to supply a positive driving current to the motor, and when steering to the left, the third control element is turned on based on the detection of the steering torque. The fourth control element is made conductive at the same time to flow a drive current in the opposite direction to the motor to rotate the motor forward and reverse, respectively, thereby controlling the steering.

[Problem to be solved by the invention]

In such a motor drive device, when the steering motor is short-circuited, a large current is applied to the first. 2nd or 3rd. Fourth
The disadvantage is that the current flows simultaneously through the switching elements of the two elements, causing damage to the elements.

The present invention has been made in view of the problems of the conventional electric power steering device, and its technical problem is to detect a short circuit in the steering motor and prevent the resulting failure. .

(Means for Solving the Problems) The present invention includes a torque sensor that is connected to a steering shaft and detects its rotational torque, a steering motor that rotates the steering wheel, and first and fourth switching elements connected to both ends of a power source. 3. The second switching element is connected in series, and the first and fourth switching elements and the third and third switching elements are connected in series.
A bridge circuit configured by connecting a steering motor symmetrically between the common connection ends of the second switching element, and a first switching element of the bridge circuit based on the output from the torque sensor.
2nd or 3rd. An electric power steering device comprising: a steering motor drive unit that controls the steering motor by driving a fourth switching element; the electric power steering device includes a current detection unit that detects whether the current flowing through the steering motor is within a predetermined range; means, a determining means for determining whether or not there is an output from the current detecting means when any of the switching elements is driven, and a cutoff control means for stopping the driving of the switching element when the determining means determines that there is a mismatched output. It is characterized by having.

[Effect]

According to the present invention having such characteristics, when driving the steering motor, it is detected whether the driving current of the motor obtained by the current detecting means during driving is within a predetermined range. Since the steering motor has an L load, when it is pulse driven, its current waveform becomes a substantially triangular waveform and falls within a predetermined range. Therefore, the current detecting means determines whether or not the current of the steering motor is within a predetermined range. If it is within this range, the steering motor is not short-circuited, and if it deviates from this range, the steering motor It is determined that there is a short circuit. Therefore, if a short-circuit condition is determined, the driving of the motor by the motor drive section is stopped to prevent damage to the switching element.

〔Effect of the invention〕

Therefore, according to the present invention, even if the steering motor, which is a load, is short-circuited, the switching element is immediately stopped to stop driving the steering motor, so the switching element can be protected and damage caused by the short circuit can be prevented. This has the effect of being able to prevent this.

[Explanation of Examples]

FIG. 2 is a schematic diagram of a power steering mechanism to which the present invention is applied, and FIG. 1 is a block diagram showing the overall configuration of its motor drive circuit. In FIG. 2, a torque sensor 2 and a transmission mechanism 3 for transmitting the steering force from the steering handle 1 are connected to the steering handle 1. The torque sensor 2 detects the torque of the steering wheel 1 in the left and right direction, and its output is given to the motor drive circuit 4. The motor drive circuit 4 is connected to a battery 5 of the vehicle, and controls a steering motor 6 that drives in the left and right direction in response to a left and right torque signal given from the torque sensor 2. The steering wheel 7 is rotated by a predetermined angle in the left-right direction.

Next, the configuration of the motor drive circuit 4 according to the first embodiment of the present application will be explained with reference to FIG. In this figure, the torque detection signal from the torque sensor 2 is transmitted to an upper FET drive section 11 and a lower FET drive section 1, which are steering motor drive sections.
given to 2. The upper FET drive unit 11 determines the positive or negative polarity from the torque sensor, and selects the first . Any third switching element, for example a power MO3FETI
3 or 14 selectively. - lower front side F
The ET drive section 12 obtains a pulse signal with a duty ratio corresponding to the absolute value of the signal obtained from the torque sensor 2, and its output is the second. It is given to the power MO3FETI5 or 16 which is the fourth switching element. Lower F
Gate circuits 18a and 18b, which are cut-off control means 17, are connected between the ET driving section 12 and the FETs 15 and 16.

1st. The fourth switching elements 13 and 16 and the third and second switching elements 14 and 15 are connected in series and connected across the battery 5, respectively. Both ends of the steering motor 6 are connected symmetrically between the common connection points of these switching elements, and the steering motor 6
A resistor 19 for current detection is provided in series with. A bridge circuit is constituted by the first to fourth switching elements 13 to 16.

Now, both ends of the current detection resistor 19 are applied to a differential amplifier 20 via a resistor circuit. The differential amplifier 20 converts the current flowing through the motor into a voltage signal, and its output is given to a window comparator 21 consisting of operational amplifiers 21a and 21b. window comparator 21
Upper and lower threshold values Vrefl and Vref2 are set, and if the voltage signal is between these values, an H level is output, and if it deviates from this range, an L level is output. Here, current detection resistor 19. The differential amplifier 20 and the window comparator 21 are current detection means 2 that detect whether the current flowing through the steering motor is within a predetermined range.
2. Now, the output of the window comparator 21 is applied to the inverting input terminal of the gate circuit 23. Also M
Two pulse outputs from the lower FET driver 12 that pulse-drive the O3FETs 15 and 16 are applied to the other input terminal of the gate circuit 23 via an OR circuit 24. The gate circuit 23 uses a signal at the moment when the FET is pulse-driven as a gate signal, and during this period, the L level output of the window comparator 21 is applied to the flip-flop 25 as a set input. Here, the gate circuit 23. The OR circuit 24 and the flip-flop 25 constitute a determining means 26 that determines whether or not there is an output from the current detecting means 22 when any switching element is driven. Now, the C output of the flip-flop 25 is transmitted to the pair of gate circuits iaa and 18b of the above-mentioned cutoff control means 17, and the FET 15
Or, the drive of 16 is stopped.

Next, the operation of this embodiment will be explained with reference to FIG. When the signal from the torque sensor 2 generates a voltage signal in either direction, for example, the positive direction, and is applied to the FET drive section 11.12, the upper FET drive section 11, for example,
When ET13 is turned on continuously, the lower FET
As shown after time 1 in FIG. This causes the steering motor 6 to be driven intermittently.Since the steering motor 6 has an L load, the motor current has a substantially triangular current waveform as shown in FIG. 3(b), and this signal is obtained from the differential amplifier 20 as a voltage signal.This signal is then sent to the window comparator 21.
A comparison is made between the threshold values Vrefl and Vref2 to see if they are within the range. Time t in Figures 3(b) and (C)
As shown after l, if it is within this range, an H level output is obtained from the window comparator 21, and the flip-flop 25 is in a reset state. Therefore, the lower F
The FETs 13 and 15 or 14 and 16 are driven by the ET driving section 12 via the gate circuits 18a and 18b.

Now, if the steering motor 6 is destroyed for some reason or the motor wiring is short-circuited, the steering motor 6 is
A large current flows through the differential amplifier 20, and a square-wave current output that changes at a large level corresponding to the drive pulse as shown in FIG. 3(b) is obtained. Therefore, since the threshold value V ref1 and V ref2 of the window comparator 21 are exceeded, an L level output is obtained from the window comparator 21 , and the flip-flop 25 is sent via the gate circuit 23 . Therefore, the gates of the gate circuits 18a and 18b are closed by the d output, and the lower F
Pulse signals are no longer applied to the FETs 15 and 16 from the ET drive section 12, and the driving of the switching elements is stopped.

In this embodiment, the lower FET drive section 12 and FET15.16 are used.
Interruption control means 1 consisting of gate circuits 18a and 18b between
7 is provided, but it goes without saying that it may be provided between the output of the upper FET drive section 11 and the FETs 13 and 14.

Further, FIG. 4 is a circuit diagram showing the configuration of a second embodiment of the present application. In this figure, the same parts as in the first embodiment are designated by the same reference numerals, and detailed explanation will be omitted.

In this embodiment, the output of the torque sensor 2 is transmitted through the upper FET 31,
Applied to lower FET 32. The upper FET drive section 31 includes power MO5FETs 13 and 14 which are switching elements.
The lower FET drive unit 32 selectively and continuously conducts the MO3FETs 15 and 16 depending on the output level of the torque sensor 2. In this case, the upper FET
A pair of outputs from the drive section 31 are given to the OR circuit 24, and the gate circuit 23 is opened and closed by the OR output. Also, the output of the upper FET 31 is connected to the gate circuits 18a and 18b.
MO3FET 13.
It is given to 14.

The other configurations are the same as those of the first embodiment described above.

In this case, the output of the upper FET driver 31 is given to the FETs 13 and 14 via the gate circuits 18a and 18b, but these gate circuits are provided on the output side of the lower FET driver 32. It is also possible.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an electric power steering device according to a first embodiment of the present invention, FIG. 2 is a schematic diagram of a power steering mechanism to which the present invention is applied, and FIG. 3 is a waveform of each part of the first embodiment. FIG. 4 is a circuit diagram of an electric power steering device according to a second embodiment of the present application. Fig. 2 1------) Lux sensor 5--Battery 6-- Steering motor 11. 3
t-knee upper FET drive section 12.32-・
-Lower FET drive section 13-16--Power MO5
FET 17--... Cutoff control means 18
a, 18b--Gate circuit 20--
Differential amplifier 21-----Window comparator 22---Current detection means 23----
-Gate circuit 24-・-OR circuit 25・-・・
-Flip-flop 26-...-Discrimination means patent applicant Tateishi Electric Co., Ltd. agent Patent attorney Yoshiki Okamoto (and one other person)

Claims (1)

[Claims] (1) A torque sensor that is connected to the steering shaft and detects its rotational torque; a steering motor that rotates the steering; first and fourth switching elements connected to both ends of the power supply;
and a second switching element connected in series, respectively, and the steering motor is connected symmetrically between common connection terminals of the first and fourth switching elements and the third and second switching elements. and a steering motor drive unit that controls the steering motor by driving the first, second, third, and fourth switching elements of the bridge circuit based on the output from the torque sensor. In the power steering device, current detection means detects whether a current flowing through the steering motor is within a predetermined range, and discrimination means determines whether or not there is an output from the current detection means when any of the switching elements is driven. An electric power steering device comprising: and a cutoff control means for stopping driving of the switching element when the discriminating means determines a mismatched output.