JP3534040B2 - 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 system 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 prevent overheating of the electric motor. The present invention relates to an electric power steering device that limits a motor current flowing through the electric motor.

[0002]

2. Description of the Related Art As disclosed in Japanese Patent Publication No. 6-51474, an electric power steering apparatus of this type determines a motor current value to be supplied to an electric motor based on a steering torque indicating a driving state of a vehicle. Then, a current according to the determined motor current value is supplied to the electric motor. Further, when the average value of the current flowing through the electric motor is larger than a predetermined value, this device executes current limiting control for gradually reducing the determined motor current value, whereby the electric motor is brought into an overheated state. I try not to become.

[0003]

However, in the above-mentioned conventional technique, the current limiting control is executed when the average value of the current flowing in the electric motor is larger than the predetermined value. When the current flowing through the electric motor is gradually reduced by the current limiting control, the average value of the current becomes smaller than the predetermined value as a result, although the current limiting control is actually in a state where it should be continued. There is a problem that the current limit control is canceled.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to address the above problems, and a first feature thereof is an electric motor that generates an assisting force for a turning operation of a steering handle,
Steering torque detecting means for detecting the steering torque of the steering wheel, command current value determining means for determining a command current value according to the detected steering torque, and whether or not the electric motor is in an overload state and overload state determining means for determining, wherein the electric motor is determined to be overloaded Tei
And a current limiting means for limiting said command current value to a predetermined value when that, in the electric power steering apparatus for a vehicle passing a motor current corresponding to the command current value is limited by the current limiting unit to the electric motor The overload state determination means determines whether or not the electric motor is in an overload state based on a current value of a motor current actually flowing in the electric motor, and the electric motor is in an overload state. After being determined to be present, it is configured to determine whether or not the overload state is continuing based on the value according to the detected steering torque.

In this case, in order to limit the command current value to a predetermined value, the command current value is limited to a constant or variable current limit value which is variable according to the vehicle speed (below the current limit value). Value), limiting to a current limit value that decreases according to the duration of the overload state, or gradually decreasing the command current value itself. The value according to the steering torque includes a value based on the command current value.

[0006] According to this, an overload condition wherein the electric motor by determining means-out <br/> that is determined to be overloaded, the command current value is a predetermined value determined according to the steering torque Limited by When the electric motor is not determined to be in an overload state, the overload state determination means determines that the electric motor is in an overload state based on the current value of the motor current actually flowing in the electric motor. And the electric motor is overloaded.
After that , it is determined whether or not the overload state continues , based on the value according to the detected steering torque. Therefore, even if the command current value is limited based on the determination that the electric motor is in an overload state and the motor current that actually flows in the electric motor decreases, for example, a value corresponding to the steering torque such as the command current value. Current limit is continuously implemented as long as is large. As a result, it is possible to appropriately avoid the situation where the electric motor falls into an overheated state.

On the other hand, when it is determined that the vehicle is not in the overload state, it is determined whether the vehicle is in the overload state based on the command current value (based on whether the command current is larger than a predetermined value). It may be possible to do so. However,
The command current value when the electric motor is in the overload state and the command current value when the assist force is required without being in the overload state may be very close to each other. If the above-mentioned overload state is determined based on only the above, there is a problem that the current limitation is performed even when the assist force is originally required instead of the overload state, and the assist force becomes insufficient.

By the way, when the electric motor is not locked and is rotating (that is, not in the overload state), the electric motor generates counter electromotive force due to rotation, and therefore the actual motor current value is It is considerably smaller than the command current value. Therefore, in the power steering control device having the above characteristics, when it is determined that the overload state is not present, the overload state is determined based on the current value of the motor current actually flowing in the electric motor. did. As a result, it is possible to reliably distinguish between the case where the vehicle is in the overload state and the case where the assisting force is required instead of the overload state, so that it is possible to appropriately limit the current.

The electric power steering system having the above-mentioned first characteristic can also have the characteristics described in the following (1) to (6).

(1) When the motor current actually flowing in the electric motor is larger than a predetermined overload judgment value (first overload judgment value), the electric motor is overloaded. When it is determined that the electric motor is in an overload state, a value (the command current value or the like) corresponding to the detected steering torque is a predetermined overload determination value (second overload determination value). ) When it is smaller than the above, the electric motor should be determined not to be overloaded. According to this, it is possible to reliably determine whether or not the vehicle is in the overload state with a simple configuration.

(2) In the electric power steering apparatus having the above-mentioned feature (1), the overload condition determining means determines that the motor current actually flowing in the electric motor is larger than a predetermined overload determining value. It should be configured to determine that the electric motor is overloaded when it continues for a predetermined time or longer. According to this, even when the steering wheel is steered to the vicinity of the end and the actual motor current temporarily becomes a large value, it is not judged that the vehicle is in the overload state. Can occur.

(3) In the electric power steering system having the above-mentioned features (1) or (2), the overload condition determination means changes the overload determination value to a smaller value as the vehicle speed increases. Be configured as follows. In this case, the overload determination value is set to a first value when the vehicle speed is "0", and is a second value smaller than the first value when the vehicle speed is other than "0". (Constant value) is included. Generally, when the speed of the vehicle is low, particularly when it is “0”, a large assist force is required. Therefore, the command current value is determined to be a larger value as the speed of the vehicle is lower. Therefore, when the steering wheel is steered to the end in a parking lot or the like provided indoors in a building or the like, the command current value and the resulting actual motor current value have a vehicle speed of "0". It doesn't grow as big as However, it is preferable to limit the motor current when the case where the vehicle runs while the electric motor is locked continues. According to the feature (3), the current limitation can be executed even in such a case, so that the electric motor can be prevented from being overheated.

(4) In the electric power steering apparatus having the first feature of the present invention or the feature described in any one of the above (1) to (3), the current limiting means is in an overload state. The command current value is set to a smaller value as the time determined to be longer is longer. According to this, it is possible to prevent overheating of the electric motor while generating the assist force to some extent.

(5) In the electric power steering apparatus having the first feature of the present invention or the feature described in any one of the above (1) to (4), the current limiting means sets the command current value to the command current value. It is configured to be limited according to the speed of the vehicle. In this case, it is preferable to limit the command current value so that the command current value becomes larger as the vehicle speed increases. According to this, it is possible to achieve appropriate current limitation according to the traveling state.

(6) In the electric power steering apparatus having the first feature of the present invention or the feature described in any one of (1) to (5), the current limiting means is provided when the vehicle is started. Alternatively, the command current value is not limited until a predetermined condition is satisfied after starting. According to this, for example, in the case where the vehicle is parked for a long time in a cold region and the wheels are frozen on the road surface and the vehicle is about to start traveling, for example, at the time of starting and only for a predetermined period after the starting. Can generate a sufficient assist force to enable the vehicle to travel (steer). In this case, the predetermined condition is that the environmental temperature of the vehicle is higher than a predetermined temperature at the time of starting the vehicle, or the integrated value of the current actually flowing in the electric motor from the start of the vehicle is the predetermined integration determination. It is advantageous that the value is greater than or equal to the value.

A second feature of the present invention is that an electric motor that generates an assisting force for the turning operation of a steering wheel, a command current value determining means that determines a command current value according to a driving state of a vehicle, and the electric motor. Is in an overload state, and when the electric motor is determined to be in an overload state, the command current value is limited by a predetermined value to obtain a motor current final output value. And a final output value calculating means for determining the command current value as a final output value of the motor current when it is determined that the electric motor is not in an overload state, and a motor current corresponding to the final output value of the calculated motor current. In the electric power steering device for a vehicle, in which the electric current is supplied to the electric motor, the overload state determination unit is configured to detect the current value of the motor current actually flowing to the electric motor and the motor. In that the electric motor when the difference is small between the flow final output value is configured to determine that there overloaded.

According to this, when the overload state determination means determines that the electric motor is in the overload state, the command current value determined according to the operating state of the vehicle is a predetermined value (current limit value). When the electric motor is determined not to be in an overload state, the command current value is set as the motor current final output value, and the motor current final output value is determined. The generated current is sent to the electric motor. Further, the overload state determination means,
When the difference between the current value of the motor current actually flowing in the electric motor and the final output value of the motor current is small, it is determined that the electric motor is in the overload state.

That is, when the electric motor is not locked and is rotating (when it is not in an overload state), the electric motor generates counter electromotive force due to rotation, and therefore the actual motor current value is It is considerably smaller than the motor current final output value. On the other hand, when the electric motor is locked and is in an overload state, the counter electromotive force does not occur, so that the current value of the motor current and the final output value of the motor current become substantially equal.

Therefore, in the electric power steering having the second feature, when the difference between the current value of the motor current actually flowing in the electric motor and the final output value of the motor current is small, the electric motor is overdriven. It was decided to determine that it was in a loaded state. As a result, it becomes possible to accurately determine whether or not the electric motor is overloaded,
Appropriate current limiting can be implemented. In addition, when the difference between the current value of the motor current and the final output value of the motor current is small, the state that the difference between the current value of the motor current and the final output value of the motor current is small continues for a predetermined time or more. When done "is naturally included.

[0020]

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. Includes an electric control circuit 10, a drive circuit 20, and a DC electric motor 30 whose energization is controlled by the drive circuit 20.
The electric control circuit 10 and the drive circuit 20 form an electric control unit 25.

The electric motor 30 gives 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, the details of the electric control unit 25 of the electric power steering apparatus shown in FIG. 1 will be described with reference to FIG.
, An input interface 12, an output interface 13, and an EEPROM 14 (Electrical Erasable PR).
OM) and a microcomputer,
The CPU 11 has a built-in memory 11a including a ROM (not shown) that stores a program and a map described later, and a RAM (not shown) that temporarily stores a calculated value when the CPU 11 executes the program.

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 board of the drive circuit 20 to detect the temperature TMPBORD of the printed 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 is supplied with power. The data supplied from the CPU 11 is stored, and the held data 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.
It should be noted that both ends of the electric motor 30 and between the resistor 20b and the switching elements Tr3, Tr4 are connected to the input interface 12, whereby the CPU 11 causes the motor terminal voltage Vt of the electric motor 30 and the motor current value IMOT.
R and can be detected.

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 electric motor 30, the electric 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 electric 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 electric motor 30 is stopped.

An ignition switch (IG switch) 2 which is switched on (closed) or off (opened) by a driver is provided on the power supply line L of the battery 50.
One end of 2 is connected. Ignition switch 2
The other end of 2 is connected to the CPU 11, the input interface 12, the output interface 13 and the EE via the diode D1.
It is connected to the PROM 14 and the steering torque sensor 35, and power is supplied to each of them when the ignition switch 22 is turned on.
The downstream side of the diode D1 is connected to the downstream side terminal of the relay 21 via a diode D2 that allows only a current flowing from the downstream side of the relay 21 to the downstream side of the diode D1, and the relay 21 is in an ON state. If it is, regardless of the state of the ignition switch 22,
Power is supplied to the CPU 11, the input interface 12, the output interface 13, the EEPROM 14, and 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. When the ignition switch 22 is in the "ON" state and the start of the engine is confirmed based on the engine speed NE in an initial routine (not shown), the CPU 11 repeatedly executes the main routine shown in FIG. That is, the CPU 11 starts the process from step 300 at a predetermined timing and then proceeds to step 310.
The basic target current value TK is calculated at. This calculation is based on the steering torque TM obtained from the steering torque sensor 35, the vehicle speed V obtained from the vehicle speed sensor 41, and the basic target current map (illustrated in step 310) stored in the memory 11a. The basic target current value TK at the time point is obtained. The basic target current map is stored for each predetermined vehicle speed (in this case, low vehicle speed, medium vehicle speed, high vehicle speed), and the CPU 11 corresponds to the vehicle speed closest to the actual vehicle speed V and the vehicle speed closest to the next vehicle speed. The basic target current value TK is obtained from each of the two basic target current maps (relation line between the vehicle speed V and the basic target current value TK), and they are interpolated with respect to the vehicle speed V to determine the final basic target current value TK. .

Next, the CPU 11 proceeds to step 320 and calculates the correction value TH. The correction value TH includes an inertia compensation current value TKAN and the like for reducing the feeling of inertia of the motor and improving the steering feeling. Inertial compensation current value TKAN
Is, for example, the steering torque TM from the steering torque sensor 35.
The time differential value (dTM / dt) of the steering torque TM is calculated from the map shown in FIG. 4 and the time differential value of the steering torque TM.
The inertia compensation current basic value TKANB that increases as the time differential value of is increased, and the gain k1 is calculated from the map shown in FIG. 5 and the actual vehicle speed V, and the product (= k1 · TK
ANB) is the final inertia compensation current value TKAN. In step 320, the CPU 11 obtains another correction value in addition to the inertia compensation current value TKAN, sets the sum of these correction values as the correction value TH, proceeds to step 330, and calculates the basic target current value TK and the correction value TH. Set the sum as the command current value ICTRL. Note that the above steps 310 to 330
Constitutes a command current value determining means.

Next, the CPU 11 proceeds to step 340 to calculate the overload current limit value IKFK. In particular,
The CPU 11 starts the processing of the subroutine shown in FIG. 6 from step 600, proceeds to step 605, and determines whether or not the value of the overload flag FKFK is “1”. The change of the value of the overload flag FKFK will be described later.

For the sake of explanation, it is assumed that the electric motor 30 is not overloaded. In this case, as described below,
Since the value of the overload flag FKFK is "0", CP
U11 makes a “No” determination at step 605 to proceed to step 610, at which the value of the overload determination current value IHAN is actually flowing through the electric motor 30 (actual motor current).
IMOTR. The actual motor current value IMOTR is the resistance 20b.
It is obtained by AD converting the potential at the connection point between the switching element Tr3 and Tr4.

Next, the CPU 11 proceeds to step 615 and determines the overload determination reference value IKJ based on the vehicle speed V and the map shown in step 615. In this example,
When the vehicle speed V is "0", the overload determination reference value IKJ is the value IKJ1
When the vehicle speed V is not "0", the overload determination reference value IKJ is made equal to the value IKJ2 (second value) smaller than the value IKJ1. Thus, the overload judgment reference value
The IKJ is changed according to the vehicle speed V because the state where the steering wheel 31 is held at the limit of its rotation range during traveling (the state where the steering wheel 31 is in the end contact) may continue, and in that case, Since the basic target current value TK is set to increase as the vehicle speed decreases, the actual motor current does not increase as much as when the vehicle speed is "0", but if no current limitation is performed, the electric motor 30 This is because it may overheat.

Subsequently, the CPU 11 proceeds to step 620 and determines whether the overload determination current value IHAN is larger than the overload determination reference value IKJ. At this point in time, the electric motor 30 is not in the overload state, so the actual motor current IMOTR value, that is, the overload determination current value IHAN is smaller than the overload determination reference value IKJ. Therefore, the CPU 11 makes a “No” determination at step 620 to proceed to step 625.
The value of the overload state continuation counter CKFK is cleared to "0". Next, the CPU 11 clears the value of the overload flag FKFK to “0” in step 630, and then executes step 635.
Clears the value of map selection flag FMAP to "0".
The value of this map selection flag FMAP is the same as in step 620 above.
When it is determined that the electric motor 30 is in the overload state in step 675, and the current limit value map is selected in step 675 described later, it is set to “1” in step 680, When it is determined that all of them have disappeared, they are cleared to "0" in step 635.

Next, the CPU 11 proceeds to step 640 and determines whether or not the value of the overload current limit prohibition flag FKIN is "1". Overload current limit prohibition flag FKIN
The value of is operated by FIGS. 9 and 10 which will be described later, but is normally "0". Therefore, the CPU 11 makes a “No” determination at step 640 to proceed to step 645 to determine whether the value of the overload flag FKFK is “1”. At this point, the value of the overload flag FKFK is "0", so the CPU 11 returns "N" in step 645.
o ”, the process proceeds to step 650, and the maximum value IMAX of the current that can flow in the electric motor 30 is set as the overload current limit value IKFK
Set (motor current maximum value IMAX). Then the CPU
11 advances to step 695 to end this routine once, and then advances to step 350 of FIG.

The CPU 11 calculates another current limit value IL in step 350. Another representative example of the current limit value IL is an ECU-side current limit value ILECU for protecting the switching elements Tr1 to Tr4 in the ECU 25 (drive circuit 20) from overheating. This ECU side current limit value I
The LECU obtains, for example, an electric motor current integral value ISUM obtained by pseudo-integrating the current value IMOTR of the electric motor 30, and calculates the electric motor current integral value ISUM, the substrate temperature TMPBORD detected by the substrate temperature sensor 23, and a predetermined value. Calculation formula (TMPECU ＝ k ・ IS
UM + TMPBORD) and switching elements Tr1 to Tr4
The estimated temperature TMPECU of is calculated, and the higher the estimated temperature TMPECU of the switching element is, the smaller value is determined.

Next, the CPU 11 proceeds to step 360 to execute the calculation routine of the motor current final output value IFINAL detailed in FIG. Specifically, in step 805, the CPU 11 compares the overload current limit value IKFK with another current limit value IL, and when the overload current limit value IKFK is larger than the other current limit value IL, In step 810, another current limit value IL is set to the final current limit value ILF, while if the overload current limit value IKFK is smaller than the other current limit value IL, in step 815 the final current limit value ILF is set. Set the overload current limit value IKFK to. At this time, the overload current limit value IKFK is equal to the above-mentioned step 650 of FIG.
At, since it is made equal to the motor current maximum value IMAX,
The CPU 11 makes a “Yes” determination at step 805 to execute step 810, whereby the final current limit value IL
F is made equal to the other current limit value IL.

Next, the CPU 11 proceeds to step 820 and determines whether or not the absolute value of the command current value ICTRL is larger than the final current limit value ILF. Then, when the absolute value of the command current value ICTRL is larger than the final current limit value ILF, it is determined in step 825 whether the command current value ICTRL is positive or negative, and when it is positive, the motor current final output value IFINAL is determined in step 830. Set the final current limit value ILF to, and if negative, set the motor current final output value IFINAL to a value (-ILF) that is the sign of the final current limit value ILF reversed in step 835, and then proceed to step 895. This routine is once ended. On the other hand, when it is determined in step 820 that the absolute value of the command current value ICTRL is smaller than the final current limit value ILF, in step 840 the motor current final output value IFINAL
The command current value ICTRL is set to, and the routine proceeds to step 895 to end this routine once.

In this way, the motor current final output value IFINAL limited by the final current limit value ILF is determined. At this point, step 65 of FIG.
At 0, the overload current limit value IKFK is the maximum motor current value IM
Since it is set to AX, the command current value ICTRL is limited by the other current limit value IL, and thus the motor current final output value IFINAL is determined. In other words, since it is determined that the electric motor 30 is not in the overload state, the current limit of the command current value ICTRL by the overload current limit value IKFK is not performed.

Thereafter, the CPU 11 determines in step 370 the motor current final output value IFINAL and the motor current value IMOT.
Based on R, 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 in the drive circuit 20 in accordance with this. As a result, a current according to the motor current final output value IFINAL flows through the electric motor 30, and an assist force corresponding to the current is applied to the steering shaft 33. And the CPU 11
Ends this routine once in step 395, and after a predetermined time, again starts the processing of this routine from step 300.

Next, a case where the electric motor 30 is changed from not overloaded to overloaded will be described. The electric motor 30 being overloaded means, for example, when the steering wheel 31 is steered until locked, or
A state in which a large motor current is applied to the electric motor 30 when the front wheels come into contact with a curb or the like during steering to lock the steered wheels.

As described above, when the electric motor 30 is in the overload state, the value of the overload flag FKFK is "0".
Is. Therefore, when executing the routine shown in FIG. 6, the CPU 11 makes a “No” determination at step 605 to execute steps 610 and 615, and proceeds to step 620. At this stage, since the electric motor 30 is in an overloaded state, the actual motor current is determined in step 610 above.
The overload determination current value IHAN for which IMOTR is set is larger than the overload determination reference value IKJ. Therefore, the CPU 11 makes a “Yes” determination at step 620 to proceed to step 655 to increase the value of the overload state continuation counter CKFK by “1”. Next, the CPU 11 determines in step 660 whether or not the value of the map selection flag FMAP is "1".
At this point, the value of the map selection flag FMAP is "0" in step 635 described above, so step 66
The judgment at 0 is “No”, and the CPU 11 makes a step 6
In step 65, it is determined whether the value of the overload state continuation counter CKFK is larger than the overload continuation time determination value CHAN.

At this moment, since the value of the overload state continuation counter CKFK has just started to increase from "0" (see step 625), the overload state continuation counter CKFK.
Is smaller than the overload duration judgment value CHAN. Therefore, the CPU 11 makes a “No” determination at step 665 to proceed to step 640, and at step 640 returns “N”.
It is determined to be “o” and the process proceeds to step 645. At this time, since the overload flag FKFK is still "0", the CPU1
In step 650, the value 1 of the overload current limit value IKFK is set to the maximum motor current value IMAX, and the process proceeds to step 695. As a result, immediately after the electric motor 30 is overloaded, the command current value ICTRL is not limited by the overload current limit value IKFK.

When the overload condition continues, the CPU 1
1 is steps 600, 605, 610, 615, 62
0,655,660,665,640,645,65
Since 0 and step 695 are repeatedly executed, the value of the overload state continuation counter CKFK is gradually increased by step 655. As a result, when the predetermined time elapses, the value of the overload state continuation counter CKFK becomes larger than the overload continuation time determination value CHAN. Therefore, the CPU 11 determines “Yes” in step 665, and the overload in step 670. Set the value of flag FKFK to "1".

Next, in step 675, the CPU 11 selects a current limit value map (limit current map) according to the vehicle speed V. This current limit value map is shown in FIG.
As shown in FIGS. 7A and 7B, when the vehicle speed V is 0 km / h, the map of FIG. 7A is selected, and when the vehicle speed V is other than 0 km / h. The map shown in FIG. 7B is selected.

The current limit value map will now be described. This map shows the current limit value IKFK on the vertical axis and the overload state continuation counter CKFK on the horizontal axis, showing the relationship between the two. Then, the map of FIG. 7A has map points (C1, I1), (C2, I2), (C
3, I3) are connected by a straight line. Also, FIG.
The map of (B) is the map points (C4, I4), (C5,
I5) and (C6, I6) are connected by a straight line.
The relationship between these map points is C1 <C2 <C4
<C5 <C3 <C6, I1>I4>I5>I2>I6>
It is I3. After that, the CPU 11 proceeds to step 680, sets the value of the map selection flag FMAP to “1”, and proceeds to step 640.

As described above, since the value of the overload current limit prohibition flag FKIN is generally "0", the CPU1
1 is determined as “No” in step 640 and then step 6
Proceed to 45. In this case, the value of the overload flag FKFK is set to "1" in the previous step 670. Therefore, the CPU
11 determines “Yes” in step 645, the process proceeds to step 685, and the current limit value map selected in the previous step 675 and the overload state continuation counter CKFK (that is,
Current limit value IK according to the time during which the overload condition continues
Determine the FK.

As a result, when the step 360 of FIG. 3, that is, the routine shown in FIG. 8 is executed, if the overload current limit value IKFK is smaller than another current limit value IL, step 8 is executed.
The final current limit value ILF is set in 15 and the command current value ICTRL is limited (reduced) by the overload current limit value IKFK in steps 820 to 840.

Next, a description will be given of the point after the point of time when it is determined that the vehicle is in the overload state based on the motor current value IMOTR actually flowing in the electric motor 30 as described above.
Since U11 repeatedly executes the main routine,
The process of the routine shown in FIG. 6 is restarted from step 600 at a predetermined timing, and the process proceeds to step 605.
At this point, the value of the overload flag FKFK is "1" in the previous step 670. Therefore, the CPU
11 determines “Yes” in step 605 and proceeds to step 690 to determine the absolute value of the command current value ICTRL as the overload determination current value IHAN (value corresponding to the command current value ICTRL, that is, the steering torque TM). Value that actually increases with increasing steering torque TM). Then, in step 615, the overload determination reference value IKJ is determined, and in step 620, it is determined whether or not the overload determination current value IHAN for which the command current value ICTRL is set is larger than the overload determination reference value IKJ. .

At this time, if the electric motor 30 is continuously overloaded, the absolute value of the output TM of the steering torque sensor 35 is large, and therefore the basic target current obtained in step 310 of the main routine shown in FIG. The absolute value of the value TK is also large, and the command current value ICTR obtained in step 330
The absolute value of L also increases. Therefore, if the overload condition continues, the CPU 11 returns “Yes” in step 620.
s ”, the process proceeds to step 655, and the value of the overload state continuation counter CKFK is further increased by“ 1 ”. And
In step 660, the value of the map selection flag FMAP is "1".
Or not.

In this case, the value of the map selection flag FMAP is
It is set to "1" in the previously executed step 680. Therefore, the CPU 11 returns “Yes” at step 660.
s ”, and the overload current limit prohibition flag FKIN
Since the value of is “0”, “No” in step 640,
Since the value of the overload flag FKFK remains “1”, it is determined “Yes” in step 645 and the process proceeds to step 685. In step 685, the value of the overload state continuation counter CKFK and the previous step 675 are performed. The current limit value IKFK is determined based on the selected current limit value map.

If the above condition continues, the value of the overload condition continuation counter CKFK gradually increases in step 655. Therefore, the current limit value selected from FIG. 7 (A) or FIG. 7 (B). As can be understood from the map, the current limit value IKFK gradually decreases and the current flowing through the electric motor 30 decreases. As a result, the electric motor 30 is controlled so as not to be overloaded while maintaining the assist force to some extent.

On the other hand, when the electric motor 30 comes out of the overloaded state, the absolute value of the output TM of the steering torque sensor 35 becomes small. As a result, the absolute value of the basic target current value TK obtained in step 310 of the main routine shown in FIG. 3 becomes smaller, and therefore the absolute value of the command current value ICTRL obtained in step 330 also becomes smaller. As a result, C
When the PU 11 repeatedly executes the routine shown in FIG. 6, the PU 11 determines “No” in step 620,
25 to 635 to execute the overload state continuation counter CKF
The values of K, the overload flag FKFK, and the map selection flag FMAP are cleared to "0". Therefore, it is determined to be “No” in step 645 following step 640, and step 65
Go to 0 and set the overload current limit value IKFK to the maximum motor current value.
As IMAX, the limit of the command current value ICTRL by the overload current limit value IKFK is released.

As described above, in the present embodiment, when it is not determined that the vehicle is in the overload state, it is determined whether the vehicle is in the overload state based on the actual motor current value IMOTR (step 605). ~ 620), when it is determined that the overload state, the value of the overload flag FKFK is set to "1" (step 670), after that, the command current value IC
It is determined by TRL whether or not the overload state continues (steps 605, 690, 615, 620). That is, steps 605-620,690,655,665
Constitutes an overload state determination means. Further, steps 675, 685 and the routine of FIG. 8 are current control means,
Also, the final output value calculating means is configured to limit the command current value ICTRL to the overload current limit value IKFK when it is determined that an overload condition exists.

This is because the actual motor current value IMOTR is limited to a value that gradually decreases by the overload current limit value IKFK after it is determined that the motor is overloaded. Current value IHAN for actual motor current value IM
If OTR is left as it is, the overload condition is released in step 620 although the current limit by the overload current limit value IKFK (current limit during overload) should actually be continued. This is because it may be determined to be (“No”) and the same current limitation may not be performed.

By the way, when it is determined that the vehicle is not overloaded, the command current value ICTRL is set to the overload determination current value IHA.
It may be possible to determine the overload state depending on whether or not it is larger than N. However, the electric motor 3
The command current value ICTRL when 0 is in the overload state and the command current value when the steering force is steered near the end (rotation limit) of the steering wheel 31 and the assist force is originally required. Since the value is very close to ICTRL, if the command current value ICTRL alone is used to determine the overload condition, the current limit during overload will be performed even when the assist force is required instead of the overload condition. I will be destroyed.
On the other hand, when the electric motor 30 is not locked and is rotating (that is, not in the overload state), the electric motor 30 generates counter electromotive force due to rotation, and therefore the actual motor current value IMOTR is It is considerably smaller than the command current value ICTRL.

Therefore, in the above embodiment, when it is determined that the electric motor 30 is not in the overload state, the overload state is determined based on the current value IMOTR of the motor current actually flowing in the electric motor 30. Decided to do. As a result, it is possible to reliably distinguish the overload state from the state in which the assist force is required but not the overload state.
It is possible to perform appropriate overload current limiting.

Further, in the above embodiment, by using the map selection flag FMAP, once it is determined that the vehicle is in the overload state, the same current limiting is performed until it is determined that the vehicle is not in the next overload state. Use a value map. This is because the current limit map is switched when the vehicle speed changes while the current limit during overload is being performed (when the vehicle goes from a stopped state to a running state or vice versa). This is to prevent a sudden change in the overload current limit value IKFK, which causes a sudden change in the motor current final output value IFINAL and a sudden change in the assist force.

Next, regarding the operation of the overload current limit prohibition flag FKIN used in step 640 of FIG. 6, C
This will be described with reference to the routines shown in FIGS. 9 and 10 that the PU 11 repeatedly executes every time a predetermined time elapses.

First, a description will be given of the case where the vehicle is started in a state where the vehicle is stopped (parked) for a long time in an environment where the outside air temperature is extremely low. The CPU 11 starts the processing of the routine shown in FIG. 9 from step 900 at a predetermined timing, and in step 905, monitors whether or not immediately after the ignition switch 22 is changed from “off” to “on”. Therefore, when the ignition switch 22 is changed from "OFF" to "ON" along with the start of driving of the vehicle, the CPU 11 makes a "Yes" determination at step 905 to proceed to step 910, where the starting current integrated value ISST is set.
The value of is cleared to "0". Next, the CPU 11 proceeds to step 915 and determines that the substrate temperature TMPBORD detected by the substrate temperature sensor 23 is a predetermined determination value TBHAN (for example, 0 ° C.).
It is determined whether or not it is smaller than the value corresponding to.

In this case, since the outside air temperature is sufficiently low and the substrate temperature TMPBORD is smaller than the predetermined judgment value TBHAN, the CPU 11 judges "Yes" in step 915 and proceeds to step 920 to determine when the overload occurs. Set the value of the current limit prohibition flag FKIN to "1", and then step 995.
Then, the routine ends once by going to. This makes CP
U11 determines “Yes” in step 640 of FIG. 6, and proceeds to step 650 to set the motor current maximum value IMAX to the overload current limit value IKFK. As a result, even if it is determined in step 620 that there is an overload, the overload current limitation is not performed.

On the other hand, the CPU 11 repeatedly executes the processing of the routine shown in FIG. 10 from step 1000, and adds the absolute value of the motor current value IMOTR at that time to the starting current integrated value ISST in step 1005. Set as a new starting current integrated value ISST. Then, the CPU 11
Advances to step 1010, and it is determined whether or not the starting current integrated value ISST is larger than a predetermined current integrated determination value ISHAN. As described in step 910 of FIG. 9, the value of the current integrated value ISST at the time of starting is cleared to “0” at the time of starting (when the ignition switch is changed from “off” to “on”). There is. Therefore, immediately after startup, the value of the integrated current value ISST at startup is the current integrated determination value ISHAN.
Smaller than Therefore, the CPU 11 executes step 1010.
Is determined as No and the routine proceeds to step 1095 to end this routine once.

After that, step 1005 is repeatedly executed, and the value of the integrated current value at start-up ISST gradually increases. For this reason, when the specified time elapses, the integrated current value at startup IS
The ST value is larger than the current integration judgment value ISHAN. As a result, the CPU 11 determines “Yes” in step 1010, proceeds to step 1015, and clears the value of the overload current limit prohibition flag FKIN to “0” in step 1015. As a result, the prohibition of the overload current limit is released, and the current limit by the overload current limit value IKFK is enabled.

Next, a case will be described in which the operation of the vehicle is started in an environment where the outside air temperature is normal (not extremely low temperature). When the ignition switch 22 is changed from “OFF” to “ON” along with the start of driving of the vehicle, the CPU 11 makes a “Yes” determination at Step 905 subsequent to Step 900 of the routine of FIG. 9 and proceeds to Step 910. Proceed and clear the current integrated value ISST at startup to "0". Next, the CPU 11 proceeds to step 915 to determine whether the substrate temperature TMPBORD detected by the substrate temperature sensor 23 is smaller than a predetermined determination value TBHAN. In this case, since the substrate temperature TMPBORD is larger than the predetermined judgment value TBHAN, the CPU 11 determines “N” in step 915.
It is determined to be "o", and the value of the overload current limit prohibition flag FKIN is cleared to "0" in step 925. As a result, the current is limited by the overload current limit value IKFK.

As described above, in this embodiment, when the outside air temperature is extremely low, the electric motor 30 is operated from the start.
The current that flows in is integrated, and the current limit during overload is prohibited until the current integration value ISST at startup becomes larger than the current integration determination value ISHAN. This is because when the outside temperature is extremely low, the steered wheels (front wheels in this example) may be stuck to the road surface due to freezing, and if the current limit during overload is immediately applied at that time, the assist force will be insufficient. This is because there is a possibility that steering cannot be performed to start traveling of the vehicle.

As described above, in this embodiment, it is determined whether or not the electric motor 30 is in the overload state based on the current value IMOTR of the motor current actually flowing in the electric motor 30. When it is determined that the electric motor 30 is overloaded (overload flag FKFK = 1)
Is the electric motor 30 based on the command current value ICTRL.
Is configured to determine whether or not is overloaded. Therefore, even when the overload current limit is applied, the overload current limit can be appropriately executed.

Next, a second embodiment of the electric power steering apparatus according to the present invention will be described. In the second embodiment, the routine shown in FIG. 6 of the first embodiment is replaced with FIG.
It differs from the first embodiment only in that the routine shown in 1 is adopted. Therefore, only FIG. 11 will be described below. In FIG. 11, the same steps as those in FIG. 6 are designated by the same reference numerals as those in FIG. 6, and detailed description thereof will be omitted.

When the CPU 11 proceeds to step 340 while executing the main routine shown in FIG.
The processing of the overload current limit value calculation routine shown in step 1100 is started from step 1100 and proceeds to step 1105, where the absolute value of the motor current final output value IFINAL and the motor current value IMOT.
Calculate ISA of the absolute value of R. Next, the CPU 11 proceeds to step 1110, where the difference ISA is the predetermined overload determination value I.
Determine if it is less than SAHAN.

As described above, when the electric motor 30 is not locked and is rotating (that is, when it is not in the overload state), the electric motor 30 produces counter electromotive force due to rotation. The motor current value IMOTR of is considerably smaller than the command current value ICTRL. In addition, in practice, the electric control unit 25 is trying to flow a current according to the motor current final output value IFINAL to the electric motor 30,
Due to the counter electromotive force, the actual motor current value IMOTR becomes considerably smaller than the motor current final output value IFINAL. On the other hand,
The electric motor 30 is locked and the electric motor 30
In the case of an overload condition in which a current is flowing through, the counter electromotive force does not occur, so the motor current value IMOTR and the motor current final output value IFINAL become equal. From the above,
When the difference ISA is smaller than the overload determination value ISAHAN, it can be determined that the electric motor 30 is in the overload state.

Therefore, when the determination at Step 1110 is "Yes", the CPU 11 determines that the electric motor 30 is in the overload state and proceeds to Step 655 and thereafter.
Limit current when overloaded. On the other hand, when it is determined to be “No” in step 1110, the process proceeds to step 625 and thereafter to cancel (stop) the overload current limitation.

As described above, in the second embodiment,
Steps 1105, 1110, 655, 665 constitute an overload state determination means, which can accurately determine whether or not the electric motor 30 is in the overload state, so that the electric motor 30 is not overheated. It becomes possible to prevent it.

Although the respective embodiments of the electric power steering system according to the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be adopted within the scope of the present invention. it can. For example, in the above-described first embodiment, when it is determined that the overload condition is present, it is determined by the command current value ICTRL whether or not the overload condition continues. Instead of the value ICTRL, the detected value TM of the steering torque sensor 35,
Alternatively, it may be configured to determine whether or not the overload state continues, based on the basic target current value TK. In the first embodiment, the value of the overload current limit prohibition flag FKIN is set to the integrated current from the start (current integrated value at start
It is cleared to "0" when ISST) becomes equal to or more than a predetermined value, but may be configured to be cleared to "0" when a predetermined time has elapsed from the start.

[Brief description of drawings]

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

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

FIG. 3 is a flowchart (main routine) showing a program executed by the CPU shown in FIG.

FIG. 4 is a map (table) of inertia compensation current basic values used by the CPU shown in FIG.

5 is a gain map (table) of an inertia compensation current basic value used by the CPU shown in FIG.

FIG. 6 is a flowchart showing a program (overload current limit value calculation routine) executed by the CPU shown in FIG.

FIG. 7 is an overload current limit value map (table) used by the CPU shown in FIG. 2, in which (A) shows a vehicle speed of 0 k.
In the case of m / h, (B) is selected when the vehicle speed is other than 0 km / h.

8 is a flowchart showing a program (motor current final output value calculation routine) executed by the CPU shown in FIG.

9 is a flowchart showing a program (current control prohibition flag operation routine during overload) executed by the CPU shown in FIG.

10 is a flowchart showing a program (overload current control prohibition flag operation routine) executed by the CPU shown in FIG.

FIG. 11 is a flowchart showing a program (overload current limit value calculation routine) executed by the CPU of the electric power steering apparatus according to the second embodiment of the present invention.

[Explanation of symbols]

10 ... Electric control circuit, 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 front page (51) Int.Cl. ⁷ Identification code FI B62D 127: 00 B62D 127: 00 137: 00 137: 00 (56) Reference JP-A-5-254454 (JP, A) JP JP-A-8-244634 (JP, A) JP-A-59-77966 (JP, A) JP-A-8-133109 (JP, A) JP-A-11-240459 (JP, A) JP-A-2001-30932 (JP, A) JP-A 1-223069 (JP, A) JP-B 6-51474 (JP, B2) (58) Fields investigated (Int.Cl. ⁷ , DB name) B62D 5/04 B62D 6/00

Claims (2)

(57) [Claims] 1. An electric motor for generating an assisting force for a turning operation of a steering wheel, steering torque detecting means for detecting a steering torque of the steering wheel, and a command current value determined according to the detected steering torque. a command current value determination means for, the overload state determining means for determining whether the electric motor is overloaded,-out <br/> and the electric motor is determined to be in an overload condition An electric power steering apparatus for a vehicle, comprising: a current limiting unit configured to limit the command current value to a predetermined value, and flowing a motor current corresponding to the command current value limited by the current limiting unit to the electric motor. The overload state determination means determines whether or not the electric motor is in an overload state based on the current value of the motor current that is actually flowing in the electric motor. After data is determined to be overloaded
The same over-it based on the value corresponding to the detected steering torque
An electric power steering apparatus, which is configured to determine whether or not a load state continues . 2. An electric motor for generating an assisting force for a turning operation of a steering wheel, a command current value determining means for determining a command current value according to a driving state of a vehicle, and whether the electric motor is overloaded. An overload state determining means for determining whether or not the electric motor is in an overload state, the command current value is limited by a predetermined value to obtain a motor current final output value, and the electric motor is A final output value calculation means for setting the command current value as a motor current final output value when it is determined that the motor is not in an overload state, and a vehicle for supplying a motor current according to the calculated motor current final output value to the electric motor. In the electric power steering apparatus, the overload state determination unit determines the current value of the motor current actually flowing in the electric motor and the final output value of the motor current. An electric power steering apparatus characterized by is configured to determine that the electric motor is overloaded when small.