JP2762370B2 - Control method of electric power steering device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a control method for an all-electric power steering device, and more particularly to a method for determining an overload.

[Conventional technology]

The conventional overload determination method is to determine an overload when the motor current exceeds a certain value over the entire steering area (the area from the left maximum angle to the right maximum angle of the steering). The current value is limited when a state determined as overload has passed a predetermined time. The reason for limiting the current value is to prevent the motor-driven transistor from being thermally damaged. The overload is, for example, when the motor current exceeds 38 A, and the current limit value when the overload state has passed for a predetermined time is, for example, 15 A.

[Problems to be solved by the invention]

As described above, in the conventional overload determination, the determination method is the same over the entire steering region. Therefore, in the steering stopper area (the maximum left and right angles of the steering and the area in the vicinity thereof), the current value is limited when the overload state has passed for a predetermined time, and the motor-driven transistor is not damaged by heat. Although effective to prevent this, the current value is similarly limited in the normal steering region (the steering region other than the stopper region), and there is a problem that the steering becomes heavy despite the steering operation.

On the other hand, by taking advantage of the feature that the overload state in the steering stopper area lasts long but the overload state in the normal area does not last long, the predetermined time during which the overload state elapses is appropriately set. A method has been proposed to prevent the current limitation in the normal region. However, there is a problem in the accuracy of the operation, and the current limitation in the normal region cannot be accurately prevented.

The present invention has been made in view of such a point,
An object of the present invention is to provide a control method for an electric power steering device in which current limitation in a steering stopper region and prevention of current limitation in a normal region are reliably performed.

[Means for solving the problem]

In order to achieve such an object, a first invention of the present application (an invention according to claim 1) detects a steering wheel torque from a torque signal from a torque sensor, and determines a motor current instruction value from the detected steering wheel torque and vehicle speed. Is calculated, and an estimated motor terminal voltage V _MSET in the snake-holding state with respect to the calculated motor current instruction value is obtained.
_MSET is _compared with the actual motor terminal voltage V _M, and V _M -V
_{When MSET} > ΔV, it is determined that the steering state is a _turning state, and when V _MSET −V _M > ΔV, it is determined that the steering state is a return state, and | V _M −V _MSET | ≦ ΔV In such a case, it is determined that the steering state is the snaking state, and the motor current is limited when the motor current value in the snaking state is equal to or more than a predetermined set value.

The second invention of the present application (the invention according to claim 2) determines the cutting state, the return state, and the snaking state by the same method as the first invention, and the duty ratio of the motor drive in the snaking state is equal to or more than a predetermined set value. In this case, the motor current is limited.

[Action]

Therefore, according to the present invention, in the first invention, the steering state is determined based on the voltage between the motor terminals and the steering wheel torque, and the motor current is limited only when the motor current value exceeds a predetermined set value in the snaking state. .

In the second invention, the steering state is determined based on the voltage between the motor terminals and the steering wheel torque, and the motor current is limited only when the motor is in the snaking state and the motor drive duty ratio exceeds a predetermined set value.

〔Example〕

FIG. 5 is a circuit diagram showing an assist motor drive control circuit of a general all-electric power steering device. In the figure, 1 is a torque sensor that outputs a torque signal a, 2 is a filter for removing noise of the torque signal a, 3 is a vehicle speed sensor that outputs a vehicle speed signal b, 4 is a CPU that controls the entire circuit, 4a Is an A / D converter of the CPU 4, 5 is a D / A converter connected to the output side of the CPU 4, 6 is a comparator, 7, 8 are AND circuits, 9 to 9
12 is a drive unit, 13 is a power switch means such as a relay, 14 to
17 is a transistor connected to the drive units 9 to 12, 18 is an assist motor, 19 and 20 are resistors for detecting a motor current, 21 is a current detector, 22 and 23 are analog switches, 24 is a buffer, and BT is a battery. It is.

Next, the general operation of the circuit of FIG. 5 will be described.
The torque signal a is input to the A / D converter 4a of the CPU 4, and the vehicle speed signal b is directly input to the CPU 4. The CPU 4 outputs a drive current value c as a command value from the signals a and b to the D / A converter 5, and outputs a right signal d and a left signal e for determining the rotation direction of the motor. The analog drive current value output from the D / A converter 5 is compared with the motor current value from the current detector 21 by the comparator 6, and if the drive current value is larger than the motor current value, the AND circuits 7, 8 And outputs "0" if the value is small. Here, assuming that the CPU 4 outputs a right signal d of “1” and a left signal e of “0”, if the drive current value is larger than the motor current value, the AND circuit 7 outputs the signal of “1”. Is output, and the drive unit 9 drives the transistor 14. Further, the drive unit 12 directly receives the right signal d from the CPU 4.
To drive the transistor 17. Therefore, the motor
A current flows from left to right through 18, and the motor 18 rotates rightward. When the drive current value is smaller than the motor current value, or when both the right signal d and the left signal e are “0”, none of the transistors is driven.

In the case of clockwise rotation, the analog switch 22 is turned on, and the voltage at the left end of the motor 18 is supplied to the CPU 4 via the buffer 24.
Is input to At this time, the voltage at the right end of the motor 18 is substantially close to the body potential of the vehicle body, and therefore, the voltage at the left end of the motor 18 is substantially the voltage between the motor terminals. In the case of the left rotation, the analog switch 23 is turned on, and the same operation is performed.

Next, an embodiment of the present invention will be described with reference to FIG. 1, FIG. 2, FIG.
This will be described with reference to FIGS. When the ignition key switch is turned on, power is supplied to the assist motor drive control circuit shown in FIG. 5, initial settings are made by clearing the memory in the CPU 4, etc., and an initial diagnosis is made as to whether there is any abnormality in the relay and the motor. (Steps 31 and 32). In the initial setting, the overload flag F is set to zero.

Next, it is determined whether or not there is an overload (step 33). Since the overload flag F is initially 0, the process proceeds to step 34 to detect the steering wheel torque (step 34). A motor current instruction value is calculated from the steering wheel torque and the vehicle speed (step 35).

A method for calculating the motor current instruction value will be described. The direction of the torque is determined from the voltage value of the torque signal a shown in FIG. This is because the CPU 4 has a map of torque on the horizontal axis and a voltage on the vertical axis as shown in FIG. Next, a torque value T is calculated using a symmetrical torque calculation map as shown in FIG. 6 (b), and a vehicle speed value s is calculated based on the vehicle speed signal b. Next, an instruction value is calculated from an instruction value (drive current value) -torque map (instruction value map) using the vehicle speed value s as a parameter as shown in FIG. 6 (c).

In this way, the motor current instruction value and its direction are calculated. Then, these values are output to the motor 18 (step 36). As a result, current flows to the motor 18, and the motor 18 starts rotating. It detects a voltage V _M between the motor terminals of this time determines the steering state (step 37). After the steering state determination, an overload determination is performed (step 38), and the process returns to step 33. If it is determined in step 33 that an overload has occurred (if the overload flag F = 1), the process proceeds to step 39 to limit the current.

The steering state determination will be described with reference to the steering state determination flowchart of FIG. First detects the motor terminal voltage V _M (detected value) (step 40). Next, the estimated motor-terminal voltage in the steering-holding state with respect to the motor current instruction value (step 35) obtained in FIG.
_MSET (search value) is obtained (step 41). This search voltage
V _MSET is obtained from the motor terminal voltage-motor current n = 0 characteristic shown in FIG. 6 (d). Fig. 6 (d)
In the above, n is a parameter of the motor rotation speed, and n =
The characteristic lines of n1, n2, and n3 show the characteristics when the clockwise drive current flows and the motor rotates clockwise, and the characteristic lines of n = -n1, -n2, and -n3 show the drive current of the counterclockwise rotation and the motor rotates. This shows the characteristics when turning left.

Then, by comparing the voltage V _M and V _MSET, V _M is the greater than V _MSET finding the value of V _M -V _MSET (step 42, 43). V _M
The value of -V _MSET is determined that the cut state is greater than [Delta] V (step 44), the value of V _M -V _MSET is determined that steering hold state when [Delta] V is smaller than (step 45). ΔV
Is a value as shown in FIG.
This is a predetermined allowable value for preventing malfunction due to noise or the like. If V _M is smaller than V _MSET in step 42, V
Determine the value of _MSET -V _M (step 46). If the value of V _MSET -V _M is greater than ΔV, it is determined that the vehicle is in the return state (step 47). If the value of V _MSET -V _M is less than ΔV, it is determined that the vehicle is in the _{steering holding} state (step 45).

Next, the overload determination will be described with reference to FIG. First, it is determined whether or not the vehicle is in a steering holding state (step 51).
This is determined using the result of the steering state determination in step 37. In the case of the steering holding state, it is determined whether or not the motor current I exceeds a predetermined set value _ISET (step 5).
2) If I ≦ I _SET , it is determined that an overload has occurred (step 5)
3). If the steering is not held in step 51, the overload flag F is reset, and the process returns to step 33 in FIG. Also,
Even if 1 ≧ I _SET is not established in step 52, the process returns to step 33 in FIG. Thus, in the steering-holding state and 1 ≧
If the I _SET condition is satisfied even once, step 33 in FIG.
Then, the process proceeds to the current limitation in step 39, and the current is limited as long as the steering is maintained. The state where the steering is maintained and 1 ≧ I _SET occurs in the stopper region of the steering wheel and does not occur in the normal region, and therefore, the current limit cannot occur in the normal region. Even if the current is not limited in the normal region, the overload state in the normal region is instantaneous, and the transistor for driving the motor is not thermally damaged.

Next, another embodiment of the overload determination will be described with reference to FIG. The overload determination in FIG. 4 is the same as steps 51, 53, and 54 in the overload determination in FIG. 3 for steps 61, 63, and 64. As shown in step 62, the duty ratio is used instead of the motor current. The difference from FIG. 3 is that only step 62 will be described. In step 62,
Duty ratio instruction value DT and predetermined duty setting value DT _SET
Bets are compared, it is determined that an overload in the case of a and DT ≧ DT _SET holding steering state, if not DT ≧ DT _SET returns to step 33 of FIG. 1.

〔The invention's effect〕

As described above, the present invention detects a steering wheel torque from a torque signal from a torque sensor, calculates a motor current instruction value from the detected steering wheel torque and vehicle speed,
An estimated motor terminal voltage V _MSET in the snaking state with respect to the calculated motor current instruction value is obtained, and the estimated motor terminal voltage V _MSET is _compared with the actual motor terminal voltage V _M, and V
_{When M−} V _MSET > ΔV, it is determined that the steering state is a _turning state, and when V _MSET −V _M > ΔV, it is determined that the steering state is a return state, and | V _M −V _MSET | When ≦ ΔV, it is determined that the steering state is the snake-holding state, and the motor current is limited when the motor current value in the snake-holding state is equal to or greater than a predetermined set value (first invention). Alternatively, the motor current is limited when the duty ratio of the motor drive in the snaking state is equal to or more than a predetermined set value (second invention), thereby preventing the current limitation in the steering stop region and the current limitation in the normal region. Can be ensured, so that the steering can be prevented from becoming heavy in the normal region.

[Brief description of the drawings]

1, 2, 3, and 4 are flowcharts for explaining an embodiment of a control method of an electric power steering apparatus according to the present invention, and FIG. 5 is a circuit diagram of an assist motor drive control circuit. FIG. 6 is a graph showing various maps stored in the memory in the CPU.

Claims (2)

(57) [Claims] An electric power steering apparatus for assisting a steering force by a motor, comprising: detecting a steering wheel torque from a torque signal from a torque sensor; calculating a motor current instruction value from the detected steering wheel torque and a vehicle speed; Obtain the estimated motor terminal voltage V _MSET in the snake-holding state with respect to the calculated motor current instruction value, compare the estimated motor terminal voltage V _MSET with the actual motor terminal voltage V _M, and _obtain V _M −V _MSET > ΔV, it is determined that the steering state is a _turning state. If V _MSET −V _M > ΔV, it is determined that the steering state is a return state, and | V _M −V _MSET | ≦ ΔV. Determining that the steering state is the snake-holding state, and limiting the motor current when the motor current value in the snake-holding state is equal to or greater than a predetermined set value. . 2. An electric power steering apparatus for assisting a steering force by a motor, comprising: detecting a steering wheel torque from a torque signal from a torque sensor; calculating a motor current instruction value from the detected steering wheel torque and vehicle speed; Obtain the estimated motor terminal voltage V _MSET in the snake-holding state with respect to the calculated motor current instruction value, compare the estimated motor terminal voltage V _MSET with the actual motor terminal voltage V _M, and _obtain V _M −V _MSET > ΔV, it is determined that the steering state is a _turning state. If V _MSET −V _M > ΔV, it is determined that the steering state is a return state, and | V _M −V _MSET | ≦ ΔV. It is determined that the steering state is the snake-holding state, and the motor current is limited when the motor drive duty ratio in the snake-holding state is equal to or greater than a predetermined set value. Control method.