JP3503436B2 - Electric motor driven steering system - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric motor-driven steering device for steering wheels of a vehicle by an electric motor. 2. Description of the Related Art Conventionally, as this type of apparatus, there is one described in, for example, Japanese Patent Application 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. The causes of the overcurrent flowing through the electric motor are not limited to the lock of the electric motor, but also the short-circuiting of the exciting coil of the electric motor, the power MOS transistor for driving the electric motor. There are various causes such as short circuit of the motor or high load of the electric motor. [0004] Due to any of these causes, a current equal to or greater than a set value does not always flow through the electric motor for a predetermined time, and in many cases, overcurrents of various magnitudes flow intermittently. For example, when the vehicle is traveling on a mountainous road, the load on the electric motor increases, and a large overcurrent flows intermittently. Also, 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 this 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 exceeding 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] In order to solve the above-mentioned problems, the present invention is an electric motor-driven steering device that steers wheels by an electric motor driven by a power MOS transistor, wherein the steering device is provided in advance. Means for obtaining a value corresponding to the average current corresponding to the average current of the predetermined time flowing through the power MOS transistor at every given time; and, whenever the value corresponding to the average current is obtained, the same average current Is compared with the first threshold value, and if the value corresponding to the same average current is equal to or greater than the first threshold value, the first duration is increased, and the value corresponding to the same average current becomes the same value. Means for initializing the first duration to 0 if not equal to or greater than the first threshold, and a value corresponding to the average current and the first threshold each time a value corresponding to the average current is obtained. Second larger
The thresholds are compared, and if the value corresponding to the average current is equal to or greater than the second threshold, the second duration is increased, and if the value corresponding to the average current is equal to or greater than the second threshold. means for initializing to zero the second duration if no, the first duration is a
When the current reaches the first time limit , the current flowing through the power MOS transistor is cut off, and the second duration time is set to the first time .
Means for interrupting a current flowing through the power MOS transistor when a second time limit shorter than the time limit is reached. According to this, power for driving the electric motor is provided.
-The time of the predetermined time flowing through the MOS transistor
A value corresponding to the average current is determined. And the average
Each time a value corresponding to the current
Is compared with the first threshold value, and the
If the value is equal to or greater than the first threshold, the first duration increases.
When the value corresponding to the average current is equal to or greater than the first threshold value,
If not, the first duration is initialized to zero. Also,
Each time a value corresponding to the average current is obtained,
A corresponding value and a second threshold greater than the first threshold
And the value corresponding to the average current is the second threshold.
If it is greater than or equal to the value, the second duration is stepped up, and
If the corresponding value is not greater than or equal to the second threshold, at the second continuation
The interval is initialized to zero. [0010] The first continuation time is set at the time of the first limit.
Current flowing through the power MOS transistor is turned off when it reaches between, the second duration during the first limit
When the second time limit shorter than the time limit is reached, the power M
The current flowing to the OS transistor is cut off. As described above, the present invention can be applied to a predetermined time.
Power based on the value corresponding to the average current
-Determine whether an overcurrent is flowing through the MOS transistor.
Not only the continuous overcurrent, but also the
An overcurrent that flows continuously can also be reliably determined.
Furthermore, according to the characteristics of the power MOS transistor,
-Size of allowable overcurrent of MOS transistor
The current can be interrupted according to the duration,
Therefore, the power MOS transistor can be used effectively.
Can be 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, the 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 the drive shaft, and a rack shaft 18 that meshes with the pinion. Move left and right,
The steering angle of each of the rear wheels 19 and 20 linked to the rack shaft 18 changes. 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 receives 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 of the rear wheels 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 and the supply voltage to the electric motor 17, etc.
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 a PWM signal having a duty ratio corresponding to the rotation speed is formed, and this PWM signal is
Output to The sub CPU 29 generates a pulse signal corresponding to the PWM signal, and notifies the driver driving and monitoring IC 30 of the pulse signal. The driver driving & monitoring IC 30 is provided with respective 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. Further, the 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.
A value Isum obtained by integrating the value IAD shown in the graph of FIG. For example, when the value IAD of the period t0 of one second 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.
The integrated value Isum1 is obtained in the graph of FIG. The sampling period of the current I is 6 ms.
ec, the current I is reduced to approximately 1 by one second.
Since sampling is performed 67 times, the current I is increased by 16
Each of the 167 values IAD obtained by sampling seven times is integrated to obtain an integrated value Isum. Therefore, the integrated value Isum indicates the 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 characteristic of the duration Timesum with respect to the current i flowing through the power MOS transistor, and shows the characteristic at each of 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 transistor failure occurs. 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. In the graph of FIG. 4, the duration Timesum that can guarantee that no transistor failure occurs is as follows:
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 or not 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 a value IAD indicating the current I 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. Further, the main CPU 28 determines the time measurement 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 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.
In the cycle of, the value IAD indicating the current I is taken in, and this value IAD
Is added to the integrated value Isum to update the integrated value Isum. At the same time, 6 msec is added to the clock time Timesum to update the clock 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 clock time Timesum reaches 1 second (step 105, Yes), and the main CPU 28 initializes the clock 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 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 per 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 CT4.5A by adding 1 second to the first duration CT4.5A (initial value = 0) (step 110), and sets the first duration CT4.5A to 30. 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 time CT9A to 0 (step 11).
3) After the integrated value Isum is initialized to 0 (step 1)
09), and return 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), and initializes the integrated value Isum 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 a current i of 4.5 A or more has flowed on average per second, or whether or not a current of 9 A or more has flowed on average per second. A 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 on average does not flow 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 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 1 second (step 110), the first duration time CT4.5A becomes 30 seconds or longer (step 111, Yes). When the first duration time CT4.5A becomes 30 seconds or more (step 111, Yes), an average of 4.times.
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 to 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 interrupted (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
Since the second step CT9A is incremented by 10 seconds (step 114), the second duration CT9A becomes 10 seconds or longer (step 115, Ye).
s). At this time, a state in which a current i of 9 A or more per second flows through the power MOS transistor for 10 seconds has continued, and this 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
If 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 a 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. In the case where a relatively small overcurrent of 4.5 A or more and less than 9 A flows in the power MOS transistor per second on average, a relatively long time of 30 seconds is exceeded, and then the power MOS transistor is turned on again for one 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. Therefore, 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 conditions for current interruption based on the time average of the current and the duration thereof are 30 seconds or more at 4.5 A or more, and 10 seconds at 9 A or more.
Not only two types of conditions, ie, seconds or more, but also three or more types of conditions may be determined. Alternatively, a function representing a relationship that the duration becomes shorter as the time average becomes larger may be determined in advance, and the duration may be derived from the time average based on this function. Further, the current interruption condition based on the time average value of the current and the duration thereof may be determined according to the characteristics of other components as well as the characteristics of the power MOS transistor . [0053] As described above, according to the present invention, in advance
To a value corresponding to the average current of the current flowing in the specified time
Overcurrent flows in the power MOS transistor based on
Or not, so it is a continuous overcurrent
In addition, it is necessary to reliably determine intermittent overcurrent
Can be. Further, the characteristics of the power MOS transistor
Combined, the allowable overcurrent of the power MOS transistor
The current can be interrupted according to the size and duration of the
This allows the power MOS transistor's ability to be
It can be used effectively. [0055]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing one embodiment of an electric motor-driven steering device of the present invention. FIG. 2 is a diagram showing a schematic configuration of a vehicle to which the steering device of this embodiment is applied. 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.
FIG. 4 is a graph showing a characteristic of a duration I Timesum with respect to a current i flowing through a power MOS transistor. FIG. 5 is a flowchart showing a process in a steering device of this embodiment. 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 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

Continuation of the front page (56) References JP-A-54-65346 (JP, A) JP-A-61-147791 (JP, A) JP-A-63-263167 (JP, A) JP-A-1-186468 (JP) JP-A-6-219289 (JP, A) JP-A-11-69865 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B62D 5/04 B62D 6/00 H02H 7/085

Claims (1)

(57) An electric motor-driven steering device for steering wheels by an electric motor driven by a power MOS transistor, wherein the power MOS transistor is connected to the power MOS transistor at predetermined time intervals. Means for determining a value corresponding to the average current flowing for the predetermined time; and, whenever a value corresponding to the average current is determined, comparing the value corresponding to the average current with a first threshold value. If the value corresponding to the average current is equal to or greater than the first threshold, the first duration is increased. If the value corresponding to the average current is not equal to or greater than the first threshold, the first duration is increased. Means for initializing to zero, and each time a value corresponding to the average current is obtained, a value corresponding to the average current is compared with a second threshold value larger than the first threshold value. If the corresponding value is greater than or equal to the second threshold The second duration is incremented if Re, and means a value corresponding to the average current to initialize to zero the second duration be not less than the second threshold value, wherein the first duration is a The current flowing through the power MOS transistor is cut off when the first time limit is reached, and the power MOS transistor is turned off when the second duration time reaches a second time limit shorter than the first time limit. An electric motor-driven steering device, comprising: means for interrupting a current flowing through the electric motor.