JPH1169611A - Electrically-driven motor drive-type steering apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrically-driven motor drive-type steering apparatus, in which whether an overcorrect flows or not can be discriminated precisely. SOLUTION: A main CPU 28 finds an average current, for one second flowing to a resistance 37. On the basis of an average current, whether an overcurrent flows to respective power MOS transistors 31a, 31b is discriminated. As a result, not only an overcurrent which flows continuously but also an overcurrent which flows intermittently can be surely discriminated. In addition, when a comparatively small overcurrent at an average of 4.5 A to less than 9 A flows for one second, a current (i) which flows to the power MOS transistors 31a, 31b is cut off after a comparatively long time of 30 seconds. In addition, when a comparatively large overcurrent at an average of 9 A or higher flows for one second, the current (i) which flows to the power MOS transistors 31a, 31b is cut off after a comparatively short time of 10 seconds.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric motor-driven steering system for steering wheels of a vehicle by an electric motor.

[0002]

2. Description of the Related Art Conventionally, as this type of apparatus, there is one described in, for example, Japanese Patent Laid-Open No. 6-219289. Here, the wheels of the vehicle are steered by an electric motor,
The current flowing through the electric motor is detected, and the steering angle of the wheel is detected. , Considers the motor locked. This prevents burning of the motor.

[0003]

The causes of the overcurrent flowing into the electric motor are not limited to the lock of the electric motor, but also the short-circuit of the exciting coil of the electric motor, the short-circuit of the power MOS transistor for driving the electric motor, and the like. Alternatively, there are various causes such as a high load of the electric motor.

[0004] Due to any of these causes, a current equal to or larger than a set value does not always flow through the electric motor for a predetermined time, and in many cases, overcurrents of various magnitudes intermittently flow. For example, when the vehicle is traveling on a mountainous road, the load on the electric motor increases, and a large overcurrent flows intermittently. In addition, when the mechanism for transmitting the power of the electric motor is oily or the mechanism is deformed by hitting a curb or the like, and the friction of the mechanism is increased, the load on the electric motor is increased and a large overcurrent is generated. Flows intermittently.

[0005] Regardless of the flow of the overcurrent, various failures can be caused. In particular, the power MOS transistor that drives the electric motor breaks down even if the overcurrent is too large and the time during which the overcurrent flows is too long.

Therefore, various failures cannot be prevented beforehand only when a current equal to or greater than a set value continues to flow through the electric motor for a predetermined time as in the above-described conventional apparatus.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and has as its object to provide an electric motor-driven steering device capable of accurately determining whether an overcurrent is flowing. And

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention relates to an electric motor-driven steering device which steers wheels by an electric motor, wherein a time average value of a current flowing through the electric motor is obtained. And determining means for determining whether an overcurrent is flowing based on the time average value.

According to such a configuration, it is determined whether or not an overcurrent is flowing based on the time average value of the current flowing through the electric motor. Therefore, it is possible to reliably determine not only an overcurrent that flows continuously but also an overcurrent that flows intermittently.

[0010] As a time average value of the current flowing through the electric motor, a total sum of the current for each predetermined time may be obtained. In this case, it is only necessary to accumulate the current flowing through the electric motor for a certain period of time. For example, the value of the current flowing through the electric motor may be repeatedly sampled during a certain period of time, and these values may be sequentially stored in the memory. This memory is
A small storage capacity is acceptable.

The determination means determines whether or not an overcurrent is flowing based on the magnitude of the time average value of the current flowing through the electric motor and the duration of the magnitude of the time average value. It may be determined that an overcurrent is flowing for a shorter duration as the value increases. In this case, for example, if a large overcurrent flows, it is immediately determined that an overcurrent is flowing. If the overcurrent is relatively small, it is determined that the overcurrent is flowing when the overcurrent continues.

[0012]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows an embodiment of an electric motor-driven steering device according to the present invention. FIG.
1 shows a schematic configuration of a vehicle to which the steering device of this embodiment is applied.

In FIG. 2, a front wheel steering mechanism 11 includes a pinion (not shown) interlocked with a steering shaft of a steering wheel 12 and a rack shaft 13 meshing with the pinion. When the pinion rotates, the rack shaft 13 moves in the left-right direction, and the steering angles of the front wheels 14 and 15 linked to the rack shaft 13 change.

The rear wheel steering mechanism 16 includes the electric motor 1.
7 (for example, a brushless motor), a pinion (not shown) interlocked with a drive shaft, and a rack shaft 18 that meshes with the pinion. When the pinion rotates with the operation of the electric motor 17, the rack shaft 18 is moved. Move left and right,
The steering angles of the rear wheels 19 and 20 linked to the rack shaft 18 change.

The steering sensor 21 detects the rotation angle of the steering shaft of the steering wheel 12. The vehicle speed sensor 22 detects the speed of the vehicle. Wheel speed sensor 23
Detects the rotational speed of the wheel. Yaw rate sensor 24
Detects the yaw rate of this vehicle. The rear wheel steering angle sensor 25 detects the steering angle of each of the rear wheels 19 and 20. The position sensor 26 detects the rotation angle of the drive shaft of the electric motor 17.

The electric motor drive type steering device 27 inputs the detection outputs of the respective sensors 21 to 26, the supply voltage to the electric motor 17, and the like, and based on these detection outputs, the supply voltage to the electric motor 17, and the like. Then, the drive control of the electric motor 17 is performed to change the steering angle of each rear wheel 19, 20.

The electric motor-driven steering device 27 is constructed as shown in FIG.
29, driver driving & monitoring IC 30, driver IC 3
1, a power supply IC 33, a memory 34, and the like.

The main CPU 28 includes sensors 21 to 26
In accordance with the target rear wheel steering angle and the current rear wheel steering angle determined based on the detection output of
The rotation direction, rotation angle, and rotation speed of the drive shaft of the electric motor 17 are determined, and each drive signal LA is determined according to the rotation direction and rotation angle.
1, LA2 ~ LC1, LC2 driver driver & monitoring IC3
0, and forms a PWM signal having a duty ratio corresponding to the rotation speed.
Output to The sub CPU 29 generates a pulse signal corresponding to the PWM signal and notifies the driver driving & monitoring IC 30 of the pulse signal.

The driver driving and monitoring IC 30 is provided with driving signals LA1, LA2 to LC1, L1 from the main CPU 28.
In response to C2, any one of the upper power MOS transistors 31a of the driver IC 31 and the lower power MOS transistors 31b of the driver IC 31
Is selected. Further, the driver driving & monitoring IC 30 controls each of the selected power MOS transistors 3 only during a period corresponding to the pulse signal from the sub CPU 29.
Turn on 1a and 31b. As a result, the current from the power supply (not shown) is changed from the fuse 35 to the relay 36 to the resistor 3.
7 → the upper power MOS transistor 31a → the electric motor 17 → the lower power MOS transistor 31b.

Such an upper power MOS transistor 31a and a lower power MOS transistor 31b
Is repeatedly selected and turned on.
Rotates by a fixed rotation angle at an appropriate rotation speed in one of the rotation directions, and the steering angles of the rear wheels 19 and 20 are changed.

A current I supplied to the electric motor 17 flows through the resistor 37 of the driver IC 31 as the selection and the ON of the upper power MOS transistor 31a and the lower power MOS transistor 31b are repeated. The driver driving & monitoring IC 30 notifies the current I. The main CPU 28 converts the current I from analog to digital (A / D conversion) and outputs a value I indicating the current I.
Generate AD.

The graph (b) in FIG. 3 shows the characteristic of the value IAD corresponding to the current I. The characteristic of the value IAD is obtained by sampling the current I periodically (6 msec) by the processing of the flowchart of FIG. 5 described later.

The graph of FIG. 3A is shown in FIG.
The value Isum obtained by integrating the value IAD shown in the graph of FIG. For example, when the value IAD of the one-second period t0 is integrated in the graph of FIG. 3B, an integrated value Isum0 is obtained in the graph of FIG. When the value IAD of the period t1 is integrated, FIG.
In the graph shown in FIG.

The sampling period of the current I is 6 ms.
ec, the current I is reduced to about 1 by one second.
Since the sampling is performed 67 times, the current I is set to 16
The 167 values IAD obtained by performing the sampling seven times are integrated to obtain an integrated value Isum.

Therefore, the integrated value Isum indicates the total sum of the current I flowing per unit time, and corresponds to the time average value of the current I.

The graph of FIG. 4 shows the characteristics of the duration Timesum with respect to the current i flowing through the power MOS transistor, and shows the characteristics at each of the temperatures 35 ° C., 60 ° C., and 85 ° C. The duration Timesum is a period that can guarantee that no transistor failure occurs when a constant current i flows.

As is clear from the graph of FIG. 4, the larger the current i flowing through the transistor, the shorter the duration Timesum that can guarantee that no failure occurs. Therefore, the larger the current i, the shorter the time the transistor will fail.

For this reason, if it is determined that an overcurrent is flowing in a short time as the current I supplied from each transistor of the driver IC to the electric motor 17 is large, the failure of each transistor is prevented beforehand. Can be.

It should be noted that the duration Timesum that can guarantee that no transistor failure occurs in the graph of FIG.
The time is sufficiently shorter than the time when a transistor failure actually occurs.

Now, in such a configuration, in order to quickly and surely detect the overcurrent of the electric motor 17 for steering the wheels, the processing of the flowchart of FIG. 5 is repeated at a predetermined cycle (for example, 6 msec). Is going.

First, the main CPU 28 controls the electric motor 1
It is determined whether an abnormal flag F indicating that an overcurrent is flowing is set in Step 7 (Step 101).
At this time, since the abnormal flag F has not been set yet (step 101, No), the main CPU 28
Captures the value IAD indicating the current I that has been A / D converted by the driver driving & monitoring IC 30 (step 10).
2). Then, the main CPU 28 confirms that the power supply voltage VIG is equal to or higher than the predetermined threshold 9.5 V (step 103, Yes), and then proceeds to step 104. If the power supply voltage VIG is less than the threshold value 9.5 V (step 103, No), the power supply voltage VIG is not high enough to guarantee the normal operation of the main CPU 28 and peripheral devices. Return.

In step 104, the main CPU 2
In step 8, the value IAD obtained in step 102 is added to the integrated value Isum (initial value = 0), and the integrated value is updated as the value Isum. The main CPU 28 also determines the time
(Initial value = 0) is added to 6 msec, and the clock time Timesum is updated to 6 msec.

Thereafter, the main CPU 28 determines the time T
After confirming that the imesum has not reached the predetermined time of 1 second (Step 105, No), Step 101
Return to

Unless the counted time Timesum reaches 1 second, the steps 101 to 105 are repeated for 6 msec.
The value IAD indicating the current I is taken in the cycle of
Is added to the integrated value Isum to update the integrated value Isum. At the same time, 6 msec is added to the counted time Timesum to update the counted time Timesum to 6 msec.

Each time steps 101 to 105 are repeated, 6 msec is added to the time measurement time Timesum.
At the time of the 67th addition, the counted time Timesum reaches 1 second (Step 105, Yes), and the main CPU 28 initializes the counted time Timesum to 0 (Step 106).

At this point, the process of taking in the value IAD indicating the current I and adding it to the integrated value Isum has been repeated 167 times. The sum of the 167 values IAD is the integrated value Isum shown in FIG.

Subsequently, the main CPU 28 determines that the integrated value Isum is equal to a predetermined first threshold value (= 15000).
It is determined whether or not this is the case (step 107). This first threshold value of 15000 corresponds to the current i = 4.5 A in the graph of FIG. Therefore, in this step 107, the integrated value Isum and the first threshold value (= 1
5000), it is determined whether or not a current i of 4.5 A or more on average flows through the power MOS transistor per second.

If the integrated value Isum is not equal to or greater than the first threshold value, that is, if an average current of 4.5 A or more does not flow in one second (step 107, No), the main CPU 2
8 initializes the first duration CT4.5A to 0 (step 108), initializes the integrated value Isum to 0 (step 109), and returns to step 101.

If the integrated value Isum is equal to or greater than the first threshold value, that is, if an average current of 4.5 A or more flows per second (step 107, Yes), the main CPU 2
8 updates the first duration time CT4.5A by adding 1 second to the first duration time CT4.5A (initial value = 0) (step 110). Seconds (step 111, N
o), proceed to step 112;

In step 112, the main CPU 2
8 is a second threshold value (=
(30000) or more. This second threshold value of 30000 corresponds to the current i =
Since this corresponds to 9.0 A, it is determined by comparing the integrated value Isum with the second threshold value (= 30000) whether or not a current i of 9 A or more on average flows through the power MOS transistor per second.

If a current i of 9 A or more on average does not flow in one second (step 112, No), the main CPU 28
Initializes the second duration CT9A to 0 (step 11).
3) After the integrated value Isum is initialized to 0 (step 1)
09), returning to step 101.

If a current i equal to or greater than 9 A averagely flows per second (step 112, Yes), the main CPU 28 sets the second duration CT9A (initial value = 0).
, The second duration CT9A is updated (step 114), and after confirming that the second duration CT9A is not longer than 10 seconds (step 11).
5, No), the integrated value Isum is initialized to 0 (step 10).
9) Return to step 101.

Accordingly, an integrated value Isum corresponding to the average current flowing through the power MOS transistor is obtained in a one-second cycle, and each time the integrated value Isum is compared with the first threshold value,
Alternatively, by comparing the integrated value Isum with the second threshold value,
It is determined whether or not current i of 4.5 A or more has flowed on average per second, or whether or not current i of 9 A or more has flowed on average per second, and current i of 4.5 A or more has flowed on average per second. If so, update the first duration time CT4.5A and average 9 times per second.
If a current i equal to or more than A flows, the second duration CT9A is updated.

However, if a current i of 4.5 A or more does not flow on average in one second, the first duration CT4.5A is initialized to 0, and a current i of 9 A or more does not flow on average in one second. For example, the second duration time CT9A is initialized to zero.

Here, when the current i of 4.5 A or more on average continues to flow in one second, this is judged (step 10).
7, Yes) is repeated, each time the first duration time CT
Since 4.5A is incremented by one second (step 110), the first duration CT4.5A is 30 seconds or longer (step 111, Yes).

When the first duration time CT4.5A becomes 30 seconds or more (step 111, Yes), the average of 4.15 seconds / sec.
This means that the state in which the current i of 5 A or more flows through the power MOS transistor continues for 30 seconds.
The main C
The PU 28 sets an abnormal flag F indicating that an overcurrent is flowing through the electric motor 17, turns on a warning lamp (not shown), notifies the effect, and turns off the contact of the relay 36. Then, the current path from the power supply to the electric motor 17 is cut off (step 116). This protects not only the power MOS transistor, but also the electric motor 17, various electronic devices, the wire harness, and the like.

If the current i of 9 A or more on average continues to flow in one second, this is judged (step 112, Ye
s) is repeated, each time the second duration time CT9A becomes 1
The second step CT9A is longer than 10 seconds (step 115, Ye).
s). At this time, the state in which a current i of 9 A or more per second flows through the power MOS transistor per second has continued for 10 seconds, which may cause a failure of the power MOS transistor. Therefore, the main CPU 28 sets the abnormal flag F. , Lighting lamp (not shown)
Is turned on to turn off the contact of the relay 36 (step 116).

That is, an average of 4.5 A or more and 9 A per second
When a relatively small overcurrent of less than 3 is flowing through the power MOS transistor, the power MOS transistor can withstand a relatively long time exceeding 30 seconds.
After 0 seconds, the current i flowing through the power MOS transistor is cut off. When a relatively large overcurrent of 9 A or more flows per second on average, the operation of the power MOS transistor can be guaranteed only for a short time of less than 10 seconds. MO
The current i flowing through the S transistor is cut off.

As described above, in the above embodiment, the power MOS
An integrated value Isum corresponding to an average current for one second flowing through the transistor is obtained, and the power MO is calculated based on the integrated value Isum.
Since it is determined whether or not an overcurrent is flowing through the S transistor, it is possible to reliably determine not only a continuously flowing overcurrent but also an intermittently flowing overcurrent.

If a relatively small overcurrent of 4.5 A or more and less than 9 A flows in the power MOS transistor per second, the power MOS transistor may exceed the comparatively long time of 30 seconds and then return to the second. When a relatively large overcurrent of 9 A or more is flowing, the current i flowing through the power MOS transistor is cut off after reaching a relatively short time of 10 seconds. For this reason, according to the characteristics of the power MOS transistor, the current can be cut off in accordance with the magnitude and duration of the allowable overcurrent of the power MOS transistor, thereby effectively utilizing the capability of the power MOS transistor. Can be.

Further, the integrated value Isum is a value IA indicating the current I.
D is taken and this value IAD is integrated and found.
It is determined by simple arithmetic processing. For example, the accumulated value Isum can be obtained by sequentially storing 167 values IAD taken 167 times per second in the RAM, and calculating the sum of the values IAD in the RAM after one second elapses. In addition, the storage capacity of the RAM may be small.

The present invention is not limited to the above embodiment, but can be variously modified. For example,
The condition of current interruption based on the time average value of the current and its duration is 30 seconds or more at 4.5 A or more, and 10
Not only two types of conditions of seconds or more, but also three or more types of conditions may be determined. Alternatively, a function indicating a relationship that the duration becomes shorter as the time average value becomes larger may be determined in advance, and the duration may be derived from the time average value based on this function. Furthermore, the condition of current interruption based on the time average value of the current and the duration thereof may be determined according to the characteristics of the power MOS transistor as well as the characteristics of other components. Further, when obtaining the duration, even if the time average value decreases to a level that cannot be said to be an overcurrent, if the reduction is temporary, the timing of the duration may be continued without interruption. .

[0053]

As described above, according to the present invention, whether or not an overcurrent is flowing is determined based on the time average of the current flowing through the electric motor. Therefore, it is possible to reliably determine not only an overcurrent that flows continuously but also an overcurrent that flows intermittently.

Further, since the total sum of the currents at predetermined time intervals is obtained as a time average value of the current flowing through the electric motor, it is only necessary to integrate the current flowing through the electric motor within a predetermined time.

Further, it is determined that an overcurrent is flowing for a shorter duration as the time average value becomes larger. For example, if a large overcurrent flows, it is determined that an overcurrent is flowing immediately. can do.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an electric motor-driven steering device according to the present invention.

FIG. 2 is a diagram showing a schematic configuration of a vehicle to which the steering device according to the embodiment is applied;

FIG. 3A is a graph showing a characteristic of an integrated value Isum obtained by integrating the value IAD shown in the graph of FIG.
(B) shows the current I flowing through the electric motor in the apparatus of FIG.
Showing the characteristic of the value IAD corresponding to

FIG. 4 is a graph showing a characteristic of a duration Timesum with respect to a current i flowing through a power MOS transistor.

FIG. 5 is a flowchart showing processing in the steering device according to the embodiment;

[Explanation of symbols]

 Reference Signs List 11 front wheel steering mechanism 12 steering wheel 13, 18 rack shaft 14, 15 front wheel 16 rear wheel steering mechanism 17 electric motor 19, 20 rear wheel 21 steering sensor 22 vehicle speed sensor 23 wheel speed sensor 24 yaw rate sensor 25 rear wheel steering angle sensor 26 position Sensor 27 Electric motor driven steering device 28 Main CPU 29 Sub CPU 30 Driver driving & monitoring IC 31 Driver IC 33 Power supply IC 34 Memory

Claims (3)

[Claims] 1. An electric motor-driven steering device for steering wheels by an electric motor, wherein a time average value of a current flowing through the electric motor is obtained, and whether an overcurrent is flowing is determined based on the time average value. An electric motor-driven steering device comprising a determination unit for determining the condition. 2. The electric motor-driven steering system according to claim 1, wherein a total sum of the current for each predetermined time is obtained as a time average value of a current flowing through the electric motor. And determining whether or not an overcurrent is flowing based on a magnitude of a time average value of a current flowing through the electric motor and a duration of the magnitude of the time average value. The electric motor-driven steering device according to claim 1, wherein it is determined that the overcurrent is flowing for a shorter duration as the value increases.