JP3409758B2 - Electric power steering device for vehicles - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering apparatus for a vehicle equipped with an electric motor for applying an assisting force to a turning operation of a steering wheel, and more particularly to a command from an actual steering torque detected. The present invention relates to an electric power steering device configured to obtain a current value and supply a current according to the command current value to the electric motor.

[0002]

2. Description of the Related Art An electric power steering apparatus of this kind stores a plurality of points, which are determined in advance by experiments, and which consist of a steering torque and a command current value, as disclosed in, for example, Japanese Unexamined Patent Publication No. 6-43187. And a command current value based on the actual steering torque detected by the torque sensor and the relationship between the steering torque and the command current value, which are configured by connecting these points with a straight line. The electric current is determined and a current corresponding to the command current value is supplied to the electric motor.

[0003]

However, in the above-mentioned conventional technique, the change amount of the command current value with respect to the unit change amount of the steering torque may change largely before and after a plurality of points determined by experiments in advance. Therefore, there are problems that the change of the assist force becomes unstable and the steering feeling is deteriorated, and the system becomes unstable and the steering system vibrates.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to address the above-described problems, and features of the present invention are an electric motor that generates a torque according to a flowing current and a steering torque that detects a steering torque of a steering wheel. A detection unit; a storage unit that stores a plurality of predetermined points composed of a steering torque and a command current value; a relationship between the steering torque and the command current value determined by the stored plurality of points; The steering wheel includes: a command current determining means for determining a command current value based on the steering torque detected by the torque detecting means; and an energizing means for supplying a current according to the determined command current value to the electric motor. In the electric power steering apparatus for a vehicle in which the electric motor applies an assisting force to the turning operation of the steering wheel, the command current determining means controls the unit change amount of the steering torque. The maximum value of the change width of the change amount of the command current value is the maximum value of the change width of the change amount of the command current value with respect to the unit change amount of the steering torque determined by connecting the plurality of stored points with a straight line. The command current value is determined so as to be smaller than the above.

According to this, the storage means stores a plurality of predetermined points consisting of the steering torque and the command current value, and the command current determining means stores the detected steering torque and the stored plurality of points. The command current value is determined based on the relationship between the steering torque and the command current value determined by the point. At this time, the command current determination means changes the command current value with respect to the unit change amount of the steering torque (that is, the steering torque on the X axis is Y).
The maximum value of the change width (the inclination change amount due to the change of the steering torque) of the straight line or the curved line when the relationship between the steering torque and the instruction current value is drawn on the axis is stored in the memory. The command current value is determined so as to be smaller than the maximum value of the change width of the change amount of the command current value with respect to the unit change amount of the steering torque, which is determined by connecting the plurality of points with a straight line.

Therefore, even when the operating state is such that the detected steering torque varies before and after a plurality of stored points, the change amount of the command current value with respect to the unit change amount of the steering torque greatly changes. Therefore, it is possible to prevent the steering feeling from being deteriorated and suppress the occurrence of vibration in the steering system.

In this case, the command current determining means has a relationship between the steering torque larger than the detected steering torque by a predetermined amount and the steering torque obtained by connecting the stored points with a straight line and the command current value. The first command current value is obtained from the above, and the first command current value is obtained from the relationship between the steering torque that is smaller than the detected steering torque by a predetermined amount and the stored steering torque that connects the plurality of points with a straight line and the command current value. 2 The command current value is calculated, and the first command current value and the second command current value are calculated.
It is preferable to determine the command current value based on the command current value. Further, the command current value determined at this time may be a simple average value of the first command current value and the second command current value, and serves as a basis for obtaining the detected steering torque and the first command current value. Difference from the steering torque (predetermined amount),
It may be a weighted average value or the like in consideration of the difference (predetermined amount) between the detected steering torque and the steering torque that is the basis for obtaining the second command current value.

According to this, since the change of the command current value can be smoothed by calculation, it is not necessary to increase the plurality of points stored in the storage means, and the capacity of the storage means is reduced. It becomes possible.

Another feature of the present invention is that an electric motor that generates a torque according to a current that is supplied, steering torque detecting means that detects a steering torque of a steering wheel, and a predetermined value that includes a steering torque and a command current value. A command current based on the relationship between the steering torque and the command current value determined by the stored points, and the steering torque detected by the steering torque detecting means. A command current determining means for determining a value and an energizing means for supplying a current according to the determined command current value to the electric motor are provided, and an assist force is applied by the electric motor to the turning operation of the steering wheel. In an electric power steering device for a vehicle, a plurality of points stored by the storage means are determined by connecting the stored points with a straight line. The maximum value of the change width of the change amount of the command current value with respect to the unit change amount of the torque of the steering torque is determined by connecting a plurality of points consisting of the steering torque and the command current value determined in advance by a straight line. This is a point set to be smaller than the maximum value of the change width of the change amount of the command current value with respect to the unit change amount.

According to this, the storage means stores a plurality of predetermined points consisting of the steering torque and the command current value, and the command current determining means stores the detected steering torque and the stored plurality of points. The command current value is determined based on the relationship between the steering torque and the command current value determined by the point. At this time, the plurality of points stored by the storage means are the change amount of the command current value with respect to the unit change amount of the steering torque determined by connecting the stored plurality of points with a straight line (that is, the steering torque on the X-axis). Is a command current value on the Y axis and the relationship between the steering torque and the command current value is drawn.
Change range (amount of change in the inclination due to change in steering torque)
The maximum value of is the maximum change width of the change amount of the command current value with respect to the unit change amount of the steering torque, which is determined by connecting a plurality of points consisting of the steering torque and the command current value that are determined in advance by a straight line. It is set to be smaller than the value.

Therefore, since the maximum value of the change width of the change amount of the command current value with respect to the unit change amount of the steering torque becomes small, the change amount does not change greatly, and the deterioration of steering feeling can be prevented. It is possible to suppress the occurrence of vibration in the steering system. Moreover, since the number of the plurality of points that must be determined by experiments can be reduced, it becomes possible to more easily provide an electric power steering apparatus having desirable characteristics.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION A first embodiment of the present invention will now be described with reference to the drawings. FIG. 1 shows a schematic block diagram of an electric power steering apparatus according to the present invention. Is an electric control unit (hereinafter referred to as “ECU”) 25 including an electric control device (circuit) 10 and a drive circuit 20 connected to the electric control device 10, and energization control by the drive circuit 20. And a DC electric motor 30.

The electric motor 30 applies an assisting force to the steering of the front wheels by the turning operation of the steering wheel (steering wheel) 31, and is attached to the steering shaft 33 via the reduction mechanism 32 so that torque can be transmitted. The rack bar 34 is driven in the axial direction according to the rotation, and the front wheels connected to the rack bar 34 via tie rods are steered. A steering torque sensor 3 is attached to the steering shaft 33.
5, the steering torque sensor 35 detects a steering torque TM acting on the steering shaft 33 and outputs a steering torque signal representing the torque.

Next, details of the electric circuit of the electric power steering apparatus shown in FIG. 1 will be described with reference to FIG. 2. The electric control apparatus 10 includes a microcomputer (CPU) 11, an input interface 12, and an output. Interface 13 and EEPROM 14 (Electric
al Erasable PROM) and CPU 11
Includes a memory 11a that stores a program, a map, and the like described later.

The input interface 12 is connected to the CPU 11 via a bus, and has the steering torque sensor 35, the vehicle speed sensor 41 for detecting the vehicle speed V, and the engine speed sensor 42 for detecting the engine speed NE, as described above.
Also, it is connected to a board temperature sensor 23 arranged on the printed circuit board of the drive circuit and detecting the temperature TMPBORD of the printed circuit board, and supplies a detection signal of each sensor to the CPU 11.

The output interface 13 is connected to the CPU 11 via the bus, and is also connected to the drive circuit 20 and the normally open type relay 21 so that they are electrically connected to each other in response to a command from the CPU 11. It sends a signal to change the state. The EEPROM 14 is a storage unit that stores and holds data even when the power is not supplied from the vehicle battery 50. The EEPROM 14 is connected to the CPU 11 via the bus and holds the data supplied from the CPU 11. At the same time, the data held therein is supplied to the CPU 11 in response to a request from the CPU 11.

The drive circuit 20 includes four switching elements Tr1 to Tr4 each having a MOSFET whose gate is connected to the output interface 13, two resistors 20a and 20b, and the substrate temperature sensor 23 described above. . One end of the resistor 20a is connected to the downstream side terminal of the relay 21 whose upstream side terminal is connected to the power supply line L of the battery 50 mounted in the vehicle, and the resistor 20a is connected to the downstream side terminal.
The other end of a is connected to the sources of the switching elements Tr1 and Tr2. The drains of the switching elements Tr1 and Tr2 are connected to the sources of the switching elements Tr3 and Tr4, respectively.
The drain of No. 4 is grounded through the resistor 20b. Further, between the switching elements Tr1 and Tr3 is connected to one side of the electric motor 30, and the switching elements Tr2 and T3 are connected.
Between r4 and the other side of the electric motor 30 is connected.
Both ends of the electric motor 30 are connected to the input interface 1
2 so that the CPU 11 inputs the voltage Vt between the motor terminals of the electric motor 30. Further, both ends of the resistor 20b are also connected to the input interface 12, and the CPU 11 can detect the motor current value IMOTR of the electric motor 30 by detecting the voltage across the resistor 20b.

With the above configuration, the drive circuit 20 (that is,
The electric motor 30) is in a state in which power can be supplied from the battery 50 when the relay 21 is turned on (closed), and when the switching elements Tr1 and Tr4 are selectively turned on (on state), the electric motor 30 When a current flows in a predetermined direction in the motor 30, the motor 30 rotates clockwise, and when the switching elements Tr2, Tr3 are selectively turned on, a current flows in the electric motor 30 in a direction opposite to the predetermined direction. The motor 30 rotates counterclockwise. When the relay 21 is turned off (opened), the power supply path of the electric motor 30 is cut off, and the power supply to the motor 30 is stopped.

An ignition switch (I / G switch), which is turned on (closed) or turned off (open) by a driver, is provided on the power supply line L of the battery 50.
One end of 22 is connected. The other end of the ignition switch 22 is connected to the CPU 11, the input interface 12, the output interface 13, and the steering torque sensor 35 via the diode D1, and when the ignition switch 22 is turned on, power is supplied to each. It has become so. Further, the downstream of the diode D1 is a diode D2 which allows only a current flowing from the downstream side of the relay 21 to the downstream side of the diode D1.
When the relay 21 is turned on by being connected to the downstream terminal of the relay 21 via the CPU 11, the CPU 11, the input interface 12, the output interface 13, regardless of the state of the ignition switch 22,
Power is supplied to the steering torque sensor 35 via the relay 21.

Next, the operation of the electric power steering device constructed as described above will be described with reference to FIGS. FIG. 3 shows a main routine executed by the CPU 11 every time a predetermined time elapses, and FIG. 4 shows the basic target current value calculation routine shown in step 310 of FIG. 3 in detail. .

First, the driver turns on the ignition switch 2
When 2 is changed from off to on, the CPU 11 executes an initial routine (not shown), and then executes the processing of the main routine shown in FIG.
00 and proceeds to step 310. CPU11
In step 310, the basic target current value TKIHON which is one of the command current values is set to the steering torque TM detected by the steering torque sensor 35 and the basic target current value shown in FIGS. It is obtained from the map (hereinafter, also simply referred to as “map”). This map is constructed by connecting a plurality of points (map points), each of which is a set of the steering torque TM and the basic target current value TKIHON determined in advance by experiment, and a straight line connecting each of these map points. Is.

More specifically, the map A in FIG. 5A is map points P0 to P3, the map B in FIG. 5B is map points P4 to P9, and the map C in FIG. 5C is map. Point P1
0 to P15, each map point is stored in the memory 11a.
Remembered in. Also, maps A, B and C
Are vehicle speeds VS1, VS2 and VS3 (VS1 <VS
2 <VS3).

The CPU 11 executes the routine shown in FIG. 4 in executing step 310. That is, C
The PU 11 starts the process from step 400, reads the current vehicle speed V and the current steering torque TM from the corresponding sensors in step 402, and in step 404, adds the predetermined amount ΔTM to the steering torque TM to obtain the upper torque. TMU,
In the following step 406, the value obtained by subtracting the predetermined amount ΔTM from the steering torque TM is set as the lower torque TMD.

Next, the CPU 11 proceeds to step 408, where the vehicle speed V is the vehicle speed VS1 associated with the map A.
If it is determined to be "Yes", it is determined in step 410 that the upper basic current value TKU (see the value a1 in FIG. 5A) is determined from the upper torque TMU and the map A. In step 412, from the lower torque TMD and the map A, the lower basic current value TKD (value a3 in FIG. 5A).
(Refer to FIG. 5A), and in step 414, the simple average value of the upper side basic current value TKU and the lower side basic current value TKD (see the value a2 in FIG. 5A) is set as the basic target current value TKIHON.
At step 495, this routine is once ended.

On the other hand, if the determination at step 408 is "No", the CPU 11 proceeds to step 416, where the vehicle speed V is the vehicle speed VS1 associated with the map A.
Above, and the vehicle speed VS2 associated with the map B
Determine if less than. And this step 4
When it is determined to be “Yes” in 16, the CPU 11
Proceeds to step 418 to determine the upper first basic current value TKU1 from the upper torque TMU and map A, and step 420
At, the lower first basic current value TKD1 is determined from the lower torque TMD and the map A. Then, the CPU 11 proceeds to step 42.
2, and at the same step 422, the upper first basic current value TK
A simple average value of U1 and the lower first basic current value TKD1 is set as the first basic target current value TK1.

Thereafter, the CPU 11 proceeds to step 424 to determine the upper second basic current value TKU2 from the upper torque TMU and the map B, and at step 426 the lower second basic current value TKU2 from the lower torque TMD and the map B. Determine the value TKD2. Next, the CPU 11 proceeds to step 428, sets the simple average value of the upper second basic current value TKU2 and the lower second basic current value TKD2 as the second basic target current value TK2 in step 428, and proceeds to step 430. The first basic current value TK1 and the second basic current value TK2 according to the formula shown in step 430.
Is interpolated with respect to the vehicle speed V, and the result is the basic target current value TK
After setting as IHON, this routine is once ended at step 495.

On the other hand, if the determination in step 416 is "No", the CPU 11 proceeds to step 432 where the vehicle speed V is the vehicle speed VS2 corresponding to the map B.
Above, and the vehicle speed VS3 associated with the map C
Determine if less than. And this step 4
If the answer in 32 is “Yes”, the CPU 11
Proceeds to step 434 to determine the upper first basic current value TKU1 from the upper torque TMU and the map B, and step 436
At, the lower first basic current value TKD1 is determined from the lower torque TMD and the map B. Then, the CPU 11 proceeds to step 43.
8, the upper first basic current value TK in step 438.
A simple average value of U1 and the lower first basic current value TKD1 is set as the first basic target current value TK1.

After that, the CPU 11 proceeds to step 440 to determine the upper second basic current value TKU2 from the upper torque TMU and the map C, and at step 442, determines the lower second basic current value TKU2 from the lower torque TMD and the map C. Determine the value TKD2. Next, the CPU 11 proceeds to step 444, sets the simple average value of the upper second basic current value TKU2 and the lower second basic current value TKD2 as the second basic target current value TK2 in step 444, and proceeds to step 446. The first basic current value TK1 and the second basic current value TK2 according to the formula shown in step 446.
Is interpolated with respect to the vehicle speed V, and the result is the basic target current value TK
After setting as IHON, this routine is once ended at step 495.

On the other hand, if the determination in step 432 is "No", the CPU 11 proceeds to step 448 where the upper basic current value TKU is determined from the upper torque TMU and the map C.
And the lower torque TM in step 450.
The lower basic target current value TKD is determined from D and the map C, and in step 452, the simple average value of the upper basic current value TKU and the lower basic current value TKD is set as the basic target current value TKIHON, and the step At 495, this routine is once ended.

As described above, when the vehicle speed V is lower than the vehicle speed VS1 associated with the map A, only the map A is used in the calculation of the basic target current value TKIHON, and the detected steering torque TM is used. The upper basic current value (first command current) TKU obtained from the torque TMU and the map A that are larger by a predetermined amount ΔTM, and the detected steering torque TM
The final basic target current value TKIHON is an average value of the torque TMD smaller by a predetermined amount ΔTM and the lower basic current value (second command current value) TKD obtained from the map A.

Therefore, as shown in FIG. 5A, the map A is constructed by connecting a plurality of points P0 to P3 determined by the steering torque TM and the basic target current value TKIHON with straight lines. , The amount of change in the basic target current value TKIHON with respect to the unit change amount of the steering torque TM before and after the points P1 and P2 (see FIG. 5).
When the slope of the straight line in (A) changes significantly (that is, when the change width (change rate, change rate) of the change amount of the basic target current value TKIHON with respect to the unit change amount of the steering torque TM is large. ), Even if the basic target current value TKIHON
It is possible to suppress a sudden change in the amount of change. In other words,
When the map points stored in the memory 11a are connected by a straight line, the change width of the change amount of the basic target current value per unit change amount of the steering torque with respect to the steering torque has the maximum value at the points P1 and P2. According to the basic target current value TKIHON obtained as described above, the maximum value of the change width can be made smaller than the change width at the points P1 and P2.

When the vehicle speed V is higher than the vehicle speed VS3 associated with the map C, the basic target current value TK
Only the map C is used in the calculation of IHON, and the basic target current value TKIHON is calculated in the same manner as when the vehicle speed V is smaller than the vehicle speed VS1 (steps 448 to 452). Therefore, the change rate of the basic target current value TKIHON is calculated. It is possible to suppress a sudden change in

On the other hand, when the vehicle speed V is the vehicle speed VS1 to VS2 or the vehicle speed VS2 to VS3, the maps A and
B and the maps B and C are selected, and the upper first and second basic current values TKU1 and T corresponding to the upper torque TMU which is larger than the steering torque TM detected for each selected map by a predetermined amount ΔTM.
KU2 and the first and second lower basic current values TK corresponding to the lower torque that is smaller than the detected steering torque TM by a predetermined amount ΔTM.
A first basic target current value TK1 and a second basic target current value TK2 are obtained from D1 and TKD2, and they are proportionally distributed (interpolated) with respect to the vehicle speed V to obtain a final basic target current value TKIHON.

Therefore, an appropriate basic target current value TKIHON for the vehicle speed is obtained, and the basic target current value TKIHON is determined.
It is possible to prevent a sudden change in the change rate of the steering wheel, and prevent the deterioration of the steering feeling and the occurrence of the vibration of the steering system.

Next, the CPU 11 causes the step 32 in FIG.
In step 0, the inertia compensation current value TKAN for reducing the feeling of inertia of the motor and improving the steering feeling is calculated.
Specifically, the steering torque TM from the steering torque sensor 35
The time differential value (dTM / dt) of the steering torque TM is 0 when the time differential value of the steering torque TM is 0, and the larger the time differential value dTM / dt of the steering torque TM, the larger the inertia compensation current In addition to obtaining the value TKANB, the gain k1 that changes according to the detected vehicle speed V (monotonically increases with respect to the vehicle speed V in the low vehicle speed range, becomes a constant value in the medium vehicle speed range, and then gradually decreases as the vehicle speed V increases), Product of these (= k1 · TKAN
B) is the final inertia compensation current value TKAN.

Next, the CPU 11 causes the step 33 in FIG.
In step 0, the steering wheel return control current value TMOD is calculated to improve the return performance (return performance to the neutral point) of the steering wheel 31 and to compensate the friction of the mechanical system due to steering. Specifically, the CPU 11 causes the voltage Vt between the terminals of the electric motor 30, the current value IMOTR of the electric motor 30, and the voltage equation (K · ω = Vt−R · IMOTR, where K is a constant,
R is the resistance value between the terminals of the electric motor 30), and the rotational angular velocity ω of the electric motor 30 is obtained, and this is multiplied by a predetermined constant to obtain a steering angular velocity estimated value STRV, and this steering angular velocity estimated value STRV and FIG. Handle return control current value map shown in
Also, the handle return control current value TMOD and the friction compensation current basic value TMASA are obtained from the friction compensation current value map shown in FIG. Then, the CPU 11 selects the steering wheel return control current value TMOD when the steering state is about to return the steering wheel 31, and selects the friction compensation current basic value TMASA when the steering wheel 31 is not about to be returned, and the selected value. Based on, the previous steering wheel return control current value TMOD is blunted to obtain the current steering wheel return control current value TMOD.

Next, the CPU 11 causes the step 34 in FIG.
In order to improve the convergence of steering at high vehicle speed and the responsiveness when the driver further steers the steering wheel 31 to a predetermined angle (cut), The damping control current value TDAMP of is calculated. Specifically, the CPU 11 causes the estimated steering angular velocity value STRV
Then, the damping control current value TDAMP is calculated from the damping control current value map shown in FIG.

Next, the CPU 11 causes the step 35 in FIG.
The ECU for proceeding to 0 to protect the switching elements Tr1 to Tr4 in the ECU 25 (drive circuit 20) from overheating
Calculate the side current limit value ILECU. Specifically, CPU1
1 is the current value IMOTR of the electric motor 30 is integrated to obtain the electric motor current integrated value ISUM, and a predetermined calculation formula (TMPECU = TPEBORD is used by using a predetermined coefficient ke3 and the substrate temperature TMPBORD detected by the substrate temperature sensor 23). ke3 · ISUM + TMPBORD) is calculated to obtain the estimated temperature TMPECU of the switching elements Tr1 to Tr4, and the ECU-side current limit value ILECU that decreases as the estimated temperature TMPECU increases is calculated.

Next, the CPU 11 executes step 3 in FIG.
In step 60, the motor-side current limit value ILMOTR for protecting the electric motor 30 from overheating is calculated. Specifically, C
The PU 11 sets a value obtained by subtracting a predetermined heat balance balance current THSQIM from the motor current value IMOTR of the electric motor 30 as the heat balance balanced current IMBARA. The heat balance balance current THSQIM is a current value at which the electric motor 30 is in an equilibrium state at a constant temperature equal to or lower than the overheating temperature even if the electric current is continuously supplied to the electric motor 30.

When the post-heat balance balance current IMBARA is equal to or greater than "0", the CPU 11 multiplies the squared post-heat balance balance current IMBARA by a predetermined positive coefficient kup. In addition to the squared motor current value SQIMSUM,
The result is a new motor current square integrated value SQIMSUM,
When the current IMBARA after heat balance is smaller than “0”, the value obtained by multiplying the value obtained by squaring the current IMBARA after heat balance by a predetermined positive coefficient kdwn is the motor current square integrated value SQIMSUM at that time. And the result is used as a new motor current square integrated value SQIMSUM. When the motor current square integrated value SQIMSUM thus obtained exceeds a predetermined threshold value, the motor current square integrated value SQIMSUM is decreased by a predetermined amount, and the motor current square integrated value is added. When the value SQIMSUM is smaller than a predetermined threshold value, a motor side current limit value ILMOTR that increases by a predetermined amount is calculated.

After the calculation of the motor side current limit value ILMOTR,
The CPU 11 proceeds to step 370 of FIG. 3 and sets the smaller one of the ECU side current limit value ILECU and the motor side current limit value ILMOTR as the final current limit value ILTEMP.

Next, the CPU 11 executes step 3 in FIG.
In step 80, the final assist current value IFINAL is calculated. Specifically, the CPU 11 sets the sum of the inertia compensation current value TKAN and the handle return control current value TMOD as the inertia / return current value TKM, and sets the basic target current value TKIHON, the inertia / return current value TKM, and the damping control current value TDAMP. When the absolute value of the assist current value ICTRL is smaller than the current limit value ILTEMP, the assist current value ICTRL is set as the final assist current value IFINAL and the absolute value of the assist current value ICTRL is calculated. When the value is larger than the current limit value ILTEMP, the current limit value ICTRL is changed depending on whether the assist current value ICTRL is positive or negative.
The final assist current value I is the positive and negative sign of LTEMP
FINAL

Next, the CPU 11 executes step 3 in FIG.
At 90, based on the final assist current value IFINAL, well-known PID control and PWM control are performed to determine the energization time of each of the switching elements Tr1 to Tr4, and a control signal is generated to the drive circuit 20 according to this. To do. as a result,
A current corresponding to the final assist current value IFINAL flows through the electric motor 30, and an assist force corresponding to the current is applied to the steering shaft 33. Then, the CPU 11 once ends this routine in step 395, and restarts the routine from step 300 again after a predetermined time.

As described above, the first aspect of the present invention
The electric power steering device of the embodiment has a steering torque.
TM controls the appropriate assist force according to the vehicle speed V. Particularly, in the present embodiment, when the basic target current value TKIHON which is the basis of the command current value is obtained, the steering torque TM and the basic target current value TKIHON are set as a set in advance by experiments and stored in the memory 11a. Based on the multiple map points (data) that were set, the final basic target current value TK so that the rate of change of the same basic current value TKIHON does not change suddenly.
Calculate IHON. Therefore, it is possible to prevent deterioration of steering feeling and occurrence of vibration of the steering system. Further, according to the first embodiment, in order to smooth the basic target current value map, more map points than necessary are stored in the memory 11a.
Since it is not necessary to store it in the memory, the storage capacity of the memory 11a can be reduced.

In the first embodiment, the basic target current value corresponding to the torque larger than the detected steering torque TM by the predetermined amount ΔTM, and the torque smaller than the detected steering torque TM by the predetermined amount ΔTM. Final basic target current value TKIHON based on simple average value with basic target current value
However, the points P0 to 0 stored in the memory 11a are determined.
Based on the data of P3, points P4 to P9, and points P10 to P15, for example, an approximate curve is calculated by the least square method, and the final basic target current is calculated from the calculated curve and the detected steering torque TM. You may ask for the value TKIHON.

In the first embodiment, the difference (ΔTM) between the upper torque TMU and the detected steering torque TM.
And the difference (ΔTM) between the lower side torque TMD and the detected steering torque TM are equal, but these values are set to different values ΔTM1 and ΔTM2, and the difference between these values ΔTM1 and ΔTM2 is taken into consideration to determine the final value. A basic target current value TKIHON can be obtained.

Next, a second embodiment of the electric power steering apparatus according to the present invention will be described. In the second embodiment, the program shown in the flowchart of FIG. 9 is executed instead of the flowchart of FIG. 4 of the first embodiment, and the basic target current value map of FIG.
It differs from the first embodiment only in that the basic target current value map shown in 0 is adopted. Therefore, the difference will be described below.

First, a basic target current value map used in obtaining the basic target current value TKIHON in the second embodiment will be described with reference to FIG.
The maps of (C) to (C) are similar to those of FIG.
It corresponds to S2 and VS3 (VS1 <VS2 <VS3), and the solid line in the figure indicates that the CPU 11 indicates the basic target current value TKIHON.
The relationship between the steering torque and the basic target current value used when calculating Further, in FIG. 10, points P0 to P
Reference numeral 15 indicates the steering torque and the basic target current value TKIHON which are experimentally obtained in advance so that the basic target current value TKIHON with respect to the steering torque TM becomes an appropriate value under the corresponding vehicle speed.
And a set of points.

As is apparent from FIG. 10, for example, FIG.
If points P0 to P3 are connected by a straight line in (A), point P
The amount of change in the basic target current value TKIHON per unit amount of change in the steering torque TM greatly differs between 1 and the point P2 (before and after). Therefore, in the present embodiment, these points P0 to P3 are not stored in the memory 11a as they are, but instead of the point P1, the points Q1 on the line segment P0-P1 are stored.
And the distance from the point P1 on the line segment P1-P2 is the point P
A point Q2 equal to the distance between 1 and Q1 is stored in the memory 11a. Regarding the point P2, instead of the point P2, a point Q3 on the line segment P1-P2 and a line segment P2-P3
The point Q4, which is above and the distance from the point P2 is equal to the distance between the points P2 and Q3, is stored in the memory 11a. That is, points P0, Q1, Q2, Q are stored in the memory 11a.
Memorize 3, Q4 and P3.

Similarly, for map B, points P4, Q5, Q6, P6, P7, Q are used instead of points P4 to P9.
7, Q8 and point P9 are stored in the memory 11a. Further, regarding the map C, since there is no point at which the amount of change in the basic target current value TKIHON per unit amount of the steering torque TM greatly changes, there are points P10 to P determined by experiments.
15 is stored as it is.

Next, the method of determining the basic target current value TKIHON in the second embodiment will be described. When executing step 310 of FIG. 3, the CPU 11 starts processing from step 900 of the program of FIG.
Read the vehicle speed V and steering torque TM. Then the CPU
11 determines in step 910 whether the vehicle speed V is lower than the vehicle speed VS1 associated with the map A, and "Yes
If it is determined to be "s", the basic target current value TKIHON is obtained from the steering torque TM and the map A in step 915, and this routine is once ended in step 995.

On the other hand, if it is determined "No" in step 910, the CPU 11 proceeds to step 920,
It is determined whether the vehicle speed V is equal to or higher than the vehicle speed VS1 associated with the map A and is smaller than the vehicle speed VS2 associated with the map B shown in FIG. When it is determined to be “Yes” in step 920, the CPU 11 proceeds to step 925, and calculates the first basic target current value TK1 from the steering torque TM and the map A.

Next, the CPU 11 proceeds to step 930 and determines the second basic target current value from the steering torque TM and the map B.
TK2 is calculated, and in step 935, the first basic current value TK1 and the second basic current value TK2 are interpolated with respect to the vehicle speed V according to the formula shown in step 935, and the result is set as the basic target current value TKIHON. At step 995, this routine is once ended.

When the determination at step 920 is "No", the CPU 11 proceeds to step 940, where the vehicle speed V is the vehicle speed VS2 corresponding to the map B.
As described above, it is determined whether or not the vehicle speed VS3 associated with the map C shown in FIG. When it is determined to be “Yes” in this step 940, the CPU 11 proceeds to step 945 to calculate the first basic target current value TK1 from the steering torque TM and the map B.

Next, the CPU 11 proceeds to step 950 and determines the second basic target current value from the steering torque TM and the map C.
TK2 is calculated, and in step 955, the first basic current value TK1 and the second basic current value TK2 are interpolated with respect to the vehicle speed V according to the formula shown in step 955, and the result is set as the basic target current value TKIHON. At step 995, this routine is once ended.

Further, when the determination in step 940 is "No", the CPU 11 proceeds to step 960 and determines the basic target current value TKIH from the steering torque TM and the map C.
ON is sought, and this routine is once ended at step 995.

As described above, in the second embodiment, it is premised that the map is constructed by linearly interpolating the points stored in the memory 11a. Instead of storing a plurality of map points (points P0 to P15) consisting of a set with the value TKIHON as they are, the change in the change amount of the basic target current value TKIHON with respect to the unit change amount of the steering torque TM is changed based on these points. A plurality of smaller map points are calculated in advance, and the calculated points and, if necessary, some of the experimentally obtained points are stored in the memory 11a.

Therefore, according to the second embodiment, as in the first embodiment, a rapid change in the rate of change of the basic target current value is suppressed, and deterioration of the steering feeling and vibration of the steering system are prevented. be able to.

In the second embodiment, point Q
The linear interpolation is performed between 1-Q2, between points Q3-Q4, between points Q5-Q6, and between points Q7-Q8.
As indicated by the one-dot chain line in (A) and (B), a curve that approximates to the line formed by the line segment connecting the plurality of points P0 to P9 obtained by the experiment is obtained by calculation in advance (that is, the points Arcs Q1 and Q2 centered on P1, arc Q centered on point P2
3 to Q4, arcs Q5 to Q6 centered on the point P5, arcs Q7 to Q8 centered on the point P8), and the representative point of the curve is stored in the memory 1
You may make it memorize | store in 1a.

As described above, the first and second aspects of the present invention
According to the embodiment, when the points consisting of the steering torque and the basic target current value (command current value) predetermined by the experiment are connected by a straight line, the basic target current value per unit change amount of the steering torque Even in the case where the maximum value of the change width of the change amount becomes large, in the first embodiment, the CPU
According to the calculation of 11, the memory 11 is used in the second embodiment.
By devising the map points stored in a, the maximum value of the change width of the change amount of the basic target current value per unit change amount of the steering torque can be reduced. As a result,
Since the change amount of the command current value with respect to the unit change amount of the steering torque does not greatly change, it is possible to prevent the deterioration of the steering feeling and suppress the vibration of the steering system.

In the first and second embodiments described above, the basic target current value map is prepared over the entire range (positive and negative) of the steering torque TM.
Only for the positive value of TM, when the steering torque TM is negative, find the basic target current value from the absolute value of the steering torque TM and the same map, and add a minus sign to the value. The basic target current value may be obtained. In this case, the number of map points stored in the memory 11a can be further reduced, so that the storage capacity of the memory 11a can be reduced. Further, by simultaneously adopting the method of the first embodiment and the method of the second embodiment,
It is also included in the present invention to further reduce the maximum value of the change width of the change amount of the basic target current value per unit change amount of the steering torque.

[Brief description of drawings]

FIG. 1 is a schematic block diagram of an electric power steering device according to a first embodiment of the present invention.

FIG. 2 is an electric circuit diagram of the electric power steering apparatus shown in FIG.

FIG. 3 is a flowchart showing a program executed by the CPU shown in FIG.

FIG. 4 is a flowchart showing a program executed by the CPU shown in FIG.

FIG. 5 is a map (table) of basic target current values.

FIG. 6 is a map of a steering wheel return control current value.

FIG. 7 is a map of a friction compensation current value.

FIG. 8 is a map of damping control current values.

FIG. 9 is a flowchart showing a program executed by a CPU according to the second embodiment of the present invention.

FIG. 10 is a basic target current value map according to the second embodiment of the present invention.

[Explanation of symbols]

10 ... Electric control device, 11a ... Memory, 20 ... Drive circuit, 21 ... Relay, 22 ... Ignition switch, 2
3 ... Substrate temperature sensor, 30 ... DC electric motor, 31 ... Steering handle, 32 ... Reduction mechanism, 33 ... Steering shaft, 35 ... Steering torque sensor, 50 ... Battery, Tr1-Tr4 ... Switching elements.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI B62D 127: 00 B62D 127: 00 137: 00 137: 00 (56) Reference JP-A-2-48271 (JP, A) JP HEI 5-85378 (JP, A) JP HEI 6-43187 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B62D 6/00 B62D 5/04

Claims (3)

(57) [Claims] 1. An electric motor that generates a torque according to a current that is supplied, a steering torque detecting unit that detects a steering torque of a steering wheel, and a plurality of predetermined points composed of a steering torque and a command current value. A storage unit that stores the command current that determines the command current value based on the relationship between the steering torque and the command current value determined by the stored points, and the steering torque detected by the steering torque detection unit. An electric power steering apparatus for a vehicle, comprising: a determining unit; and an energizing unit that supplies a current according to the determined command current value to the electric motor, and applies an assist force to the turning operation of the steering handle by the electric motor. In the command current determining means, the maximum value of the change width of the change amount of the command current value with respect to the unit change amount of the steering torque is The electric power steering apparatus is characterized in that the command current value is determined so as to be smaller than the maximum value of the change width of the change amount of the command current value with respect to the unit change amount of the steering torque determined by connecting the . 2. The command current determining means determines the steering torque larger than the detected steering torque by a predetermined amount and the relationship between the steering torque and the command current value in which the stored points are connected by a straight line. A second command is obtained from the relationship between the steering torque obtained by obtaining the first command current value and the steering torque smaller than the detected steering torque by a predetermined amount and the stored steering torque obtained by connecting the plurality of points with a straight line, and the command current value.
The electric power steering apparatus according to claim 1, wherein a command current value is obtained, and the command current value is determined based on the first command current value and the second command current value. 3. An electric motor for generating a torque according to a flowing current, a steering torque detecting means for detecting a steering torque of a steering wheel, and a plurality of predetermined points composed of a steering torque and a command current value. A storage unit that stores the command current that determines the command current value based on the relationship between the steering torque and the command current value determined by the stored points, and the steering torque detected by the steering torque detection unit. An electric power steering apparatus for a vehicle, comprising: a determining unit; and an energizing unit that supplies a current according to the determined command current value to the electric motor, and applies an assist force to the turning operation of the steering handle by the electric motor. In the above, in the plurality of points stored by the storage means, the unit change amount of the steering torque determined by connecting the plurality of stored points with a straight line. The maximum value of the change width of the change amount of the command current value to the command for the unit change amount of the steering torque is determined by connecting a plurality of points consisting of the steering torque and the command current value, which are previously determined by experiments, with a straight line An electric power steering apparatus, characterized in that the point is set to be smaller than a maximum value of a change width of a change amount of a current value.