JP2002370659A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device for preventing an increase in electric power consumption more than necessary by cutting off current- carrying to a control device as quickly as possible without causing the possibility of overheat of a motor after restarting when performing current-carrying cutoff operation in the middle of control for limiting an indicator current to the steering assisting force generating motor for preventing an overload. SOLUTION: The upper limit value of the indicator current to the steering assisting force generating electric motor is limited according to a limiting condition preset by the control device. When performing the current-carrying cutoff operation to the control device in the middle of limiting the upper limit value of the indicator current to the motor, when ambient temperature of the motor detected by a temperature sensor is less than a preset value, the current-carrying to the control device is cut off.

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 generating a steering assist force by an electric motor.

[0002]

2. Description of the Related Art In an electric power steering apparatus,
In order to prevent the electric motor for generating the steering assist force from being overheated due to overload, the upper limit value of the command current to the motor is limited according to a preset restriction condition.

For example, as a limiting condition, a set value of a variable corresponding to a motor load, such as a continuous driving time of the motor at the start of the limit and an integrated value of a supplied current, is determined in advance, and when the variable reaches the set value, The upper limit value of the command current is reduced from the maximum value to the minimum value, and thereafter, is restored from the minimum value to the maximum value. By gradually reducing and returning the upper limit value of the command current, overheating of the motor and the control device is prevented and cooling is performed. By returning the upper limit value of the command current to the maximum value, the steering feeling can be favorably maintained without the steering assist force becoming insufficient more than necessary.

Conventionally, when the ignition key switch of the vehicle is turned off while the upper limit value of the command current to the motor is being limited, the current supply to the motor is not interrupted immediately without interrupting the power supply to the control device. Power supply is cut off after the upper limit value has returned to the maximum value. This prevents the motor from overheating when the ignition key switch is turned off and then turned on and restarted in a short time.

[0005]

The limitation condition of the upper limit value of the command current to the steering assist motor is determined on the assumption that the vehicle is driving. Since the steering assist motor is frequently driven while the vehicle is operating, it is necessary to cool the motor sufficiently long after returning to the maximum value after limiting the upper limit of the indicated current. There is. However, after the ignition key switch is turned off and the energization cutoff operation is performed, the steering assist motor is not driven. Therefore, if the power cutoff operation is performed while the upper limit value of the command current to the steering assist motor is being limited,
The time required for the upper limit value of the command current of the motor to return to the maximum value becomes unnecessarily long, and the power supply to the control device is not interrupted until the return, so that power is consumed more than necessary.

[0006]

SUMMARY OF THE INVENTION The present invention is applied to an electric power steering apparatus provided with a control device for limiting an upper limit value of a command current to an electric motor for generating a steering assist force in accordance with a preset limit condition. .

A first feature of the present invention is that a temperature sensor for detecting the ambient temperature of the electric motor and a means for determining whether the detected ambient temperature is lower than a predetermined set value are provided. If the detected ambient temperature is less than the set value when the power supply cutoff operation is performed on the control device while the upper limit value of the instruction current to the electric motor is being limited, the power supply to the control device is performed. Is to be cut off.
According to this configuration, when an energization cutoff operation to the control device is performed while the upper limit value of the instruction current to the electric motor is being limited, whether the detected ambient temperature is lower than a predetermined set value or not. By determining whether or not the electric motor is cooled, it can be determined whether or not the electric motor has been sufficiently cooled so as not to cause overheating after the restart. This makes it possible to cut off the power supply to the control device as quickly as possible without causing the electric motor to overheat after the restart.

According to a second feature of the present invention, there is provided means for determining whether or not an elapsed time since the power-off operation to the control device is equal to or greater than a predetermined set value. The point is that when an operation to cut off the power supply to the control device is performed while the upper limit value of the command current is being limited, if the elapsed time is equal to or longer than the set value, the power supply to the control device is cut off. According to this configuration, when the power cutoff operation is performed on the control device while the upper limit value of the command current to the electric motor is being limited, the elapsed time since the power cutoff operation is performed is predetermined. By determining whether or not the value is equal to or greater than the set value, it is possible to determine whether or not the electric motor has been sufficiently cooled so as not to cause overheating after restart. This makes it possible to cut off the power supply to the control device as quickly as possible without causing the electric motor to overheat after the restart.

In the present invention, it is preferable to have both the first feature and the second feature.

As the limiting conditions, the reference current corresponding to the integrated value of the current supplied to the electric motor at the start of the limitation, the minimum value of the upper limit of the indicated current, and the lower limit of the upper limit of the indicated current are reduced. The rate of increase when increasing to the maximum value is set in advance, and when the integrated value of the supplied current exceeds the square value of the reference current, the reduction of the indicated current from the upper limit value is started, and the supplied current is reduced. When the integrated value exceeds the square of the minimum value of the upper limit value of the indicated current, the upper limit value of the indicated current is set to the minimum value, and then the maximum value is increased at the increasing speed, and the reference current is set. The lower the set ambient temperature, the greater the lower the set ambient temperature, and the higher the speed, the lower the set ambient temperature. Fast It is preferable to that. Thereby, the upper limit of the instruction current to the electric motor can be appropriately limited.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In an electric power steering apparatus 1 shown in FIG. 1, a steering shaft 2 connected to a steering wheel H of a vehicle is connected to wheels 4 via a steering gear 3. The steering gear 3 is a rack and pinion type in this embodiment,
A pinion 6 is connected to the steering shaft 2 via a universal joint 5, and a rack 7 that meshes with the pinion 6. The wheels 4 are connected to the rack 7 via a link mechanism. As a result, the rotation of the steering wheel H is transmitted to the rack 7 via the steering shaft 2 and the pinion 6, and the movement of the rack 7 changes the toe angle of the wheel 4 to perform steering. The steering gear 3 only needs to be able to transmit the movement of a member operated by the driver's steering to the wheels such that the steering angle changes, and may be, for example, a ball screw type.

The output of the electric motor 10 for generating a steering assist force is transmitted to the wheels 4 via an output transmission mechanism. The output transmission mechanism has a driven gear 11 provided on the steering shaft 2 and a drive gear 12 meshed with the driven gear 11, and the drive gear 12 is driven by the motor 10 to generate a steering assist force. I do. The output transmission mechanism controls the output of the motor 10 so that the steering angle changes.
For example, a screw integrated with a rack of a rack and pinion type steering gear and a nut screwed to the screw may be used, and the nut may be driven by the motor 10.

As a steering assist reference value for determining the steering assist force, a torque sensor 21 for detecting a steering torque transmitted by the steering shaft 2 and a vehicle speed sensor 22 for detecting a vehicle speed are connected to an on-vehicle control device 23. Have been. Note that the steering assist reference value is not particularly limited as long as it is a reference for determining the steering assist force. For example, a steering angle may be employed.

A current detection sensor 25 for detecting a current value of the motor 10 and a temperature sensor 26 for detecting an ambient temperature of the motor 10 are connected to the control device 23. The structure and arrangement of the temperature sensor 26 are not limited as long as the temperature sensor 26 can detect the ambient temperature of the motor 10. For example, the temperature sensor 26 is connected to the motor 10 or the controller 23.
Or the housing 23a of the control device 23.
It may be arranged inside.

The control device 23 includes the torque sensor 2
An instruction current value is calculated in accordance with the steering torque detected by step 1 and the vehicle speed detected by the vehicle speed sensor 22. That is, the control device 23 stores a preset relationship between the steering torque, the vehicle speed, and the command current value, and calculates the command current value from the stored relationship, the detected steering torque, and the vehicle speed. The stored relationship is determined, for example, such that the steering assist force increases as the steering torque increases and the vehicle speed decreases. The control device 23 obtains a command voltage so as to eliminate a deviation between the current value detected by the current detection sensor 25 and the command current value by performing PID control, for example, and outputs the command voltage to the motor 10. I do.

The control device 23 stores limiting conditions for limiting the upper limit value of the command current to the motor 10,
The upper limit value of the command current to motor 10 is limited according to the limiting condition. The limiting condition is set in advance so that overheating of the motor 10 due to overload of the motor 10 can be prevented.

In this embodiment, when the integrated value of the energizing current Im of the motor 10 exceeds the square value of the predetermined reference current Ia, the upper limit value of the indicated current is reduced from the maximum value Imax to the minimum value Imin. To start that. Further, when the integrated value becomes less than the square of the predetermined minimum value Imin of the upper limit value of the instruction current, the controller starts to increase the upper limit value of the instruction current from the minimum value Imin to the maximum value Imax. As the limiting conditions, the reference current Ia, the minimum value Imin of the upper limit of the indicated current, and the upper limit of the indicated current are set to the minimum value.
The increase speed when increasing from Imin to the maximum value Imax is set in advance. The maximum value Imax of the upper limit value of the command current is determined in advance from the specification of the motor 10 according to the maximum steering assist force required by the electric power steering device 1. The limiting condition and the maximum value Imax of the upper limit value of the command current are stored in the control device 23.

Here, the integrated value of the energizing current Im correlates with the heat generation amount of the motor 10, and the heat generation amount of the motor 10 correlates with the square of the energizing current Im. Therefore, M is determined by the conduction current I
integrated value of m, Laplace operator and s, as a transfer function of G (s), by M = G (s) · Im 2 can be obtained an integrated value of electric current Im to approximately. In the present embodiment, assuming that G (s) = 1 / {(1000 + s) · s}, the integrated value M of the conduction current Im = Im ² / {(1000 + s)}.
S}, and when the integrated value M exceeds the square value of the reference current Ia, that is, Im ² / ｛(1000 + s).
When s｝> Ia ² , the limitation of the upper limit value of the command current is started. Note that the transfer function G (s) is an example, and any transfer function G (s) may be used as long as the integrated value of the conduction current Im can be approximately obtained. The square value of the reference current Ia is determined as follows. The motor 10 is energized when the motor 10 is continuously driven for an allowed time ta while the maximum value Imax of the upper limit of the indicated current is energized at a predetermined ambient temperature. It is determined so as to correspond to the integrated value of the current. The minimum value Imin of the upper limit value of the command current is set such that continuous driving of the motor 10 is allowed at a predetermined atmospheric temperature while the minimum value Imin is energized. At the predetermined ambient temperature, the upper limit of the indicated current is the minimum value
In the state of Imin, the motor 10 can be driven continuously if the square value of the conduction current Im correlated to the heat generation amount of the motor 10 becomes smaller than the square value of the minimum value Imin of the upper limit of the command current. . Therefore, in the present embodiment, when the integrated value M of the conduction current Im correlated with the heat generation amount of the motor 10 becomes less than the square of the minimum value Imin of the upper limit value of the indicated current, the upper limit value of the indicated current is reduced. To release the limit, set the upper limit of the indicated current from the minimum value Imin to the maximum value.
Start increasing to Imax.

The limiting condition is set so that the lower the set ambient temperature of the motor 10, the more the temperature is reduced. That is, the reference current Ia corresponding to the allowable continuous driving time ta of the motor 10 and the minimum value Im of the upper limit value of the indicated current.
In is increased as the set ambient temperature is lower. Further, the increasing speed is increased as the set ambient temperature is lower.

FIG. 2 shows an example of the stored limiting condition. In this embodiment, the limiting condition is as follows.
The set atmosphere temperature is less than 25 ° C, 25 ° C to 30 ° C,
30 ° C to 35 ° C, 35 ° C to 40 ° C, 40 ° C to 45 ° C, 4
5 ° C to 50 ° C, 50 ° C to 55 ° C, 55 ° C to 60 ° C, 60
For each of the reference temperature ranges of ° C to 65 ° C, 65 ° C to 70 ° C, and 70 ° C or higher, the temperature is preset and stored in the control device 23.
That is, the maximum value Im of the upper limit value of the instruction current to the motor 10
The reference current Ia associated with the allowable continuous drive time ta of the motor 10 at ax (65 amps in the present embodiment), the minimum value Imin of the upper limit of the instruction current to the motor 10, and the upper limit of the instruction current are The increase speed Vi when increasing from the minimum value Imin to the maximum value Imax is stored for each reference temperature range of the set atmosphere temperature.

FIG. 3 shows an example of the relationship between the allowable continuous drive time ta of the motor 10 and the upper limit value of the command current to the motor 10. In the illustrated example, the set ambient temperature is less than 25 ° C. The maximum value Imax of the upper limit value of the indicated current is 6
5 amps.

FIG. 4 shows an example of the relationship between the upper limit value of the command current to the motor 10 and the integrated value M of the energizing current. When the integrated value M is the square value of the reference current Ia, the upper limit value is the maximum value.
When the integrated value M is the square value of the minimum value Imin of the upper limit, the upper limit becomes the minimum value Imin. In the present embodiment, the upper limit value of the indicated current is obtained by linear interpolation until the integrated value M exceeds the square value of the reference current Ia and reaches the square value of the minimum value Imin of the upper limit value. It is assumed that the upper limit value of the command current gradually decreases. In the illustrated example, the set atmosphere temperature is less than 25 ° C., and its maximum value Imax
Is 65 amps. In the example of FIG. 2, when the ambient temperature is equal to or higher than 65 ° C., the minimum value Imin of the upper limit of the command current is smaller than the reference current Ia. In such a case, when the integrated value M exceeds the square value of the reference current Ia, the upper limit value of the indicated current does not gradually decrease from the maximum value Imax but immediately becomes the minimum value Imin.

FIG. 5 shows an example of the relationship between the upper limit value of the command current and the time when the upper limit value of the command current to the motor 10 is increased from the minimum value Imin to the maximum value Imax. Ambient temperature is less than 25 ° C, its maximum value Im
ax is set to 65 amps.

The control procedure of the motor 10 by the control device 23 will be described with reference to the flowchart of FIG. First, the ambient temperature of the motor 10 is set (the reference temperature range in FIG. 2 is set) (step 1), and the value of the energizing current Im of the motor 10 detected by the current detection sensor 25 is read (step 2). Next, the integrated value M of the supplied current Im is calculated as M = Im ² / {(1000 + s) · s} (Step 3), and it is determined whether or not the integrated value M is equal to or less than the square of the reference current Ia (Step 4). ). If the integrated value M is equal to or less than the square value of the reference current Ia, the process returns to step 1. When the integrated value M exceeds the square value of the reference current Ia, for example, as shown in FIG. 4, the current is supplied between the minimum value Imin and the maximum value Imax of the upper limit value of the command current corresponding to the set ambient temperature. The upper limit of the command current of the motor 10 is reduced according to the relationship between the integrated value M of the current Im and the upper limit of the command current (step 5). Next, it is determined whether or not the upper limit value of the command current has reached the minimum value Imin (step 6), and if not, the process returns to step 5. If the upper limit value of the command current reaches the minimum value Imin, the upper limit value of the command current to the motor 10 is increased from the minimum value Imin to the maximum value Imax at the increase speed Vi corresponding to the set ambient temperature ( Step 7). Next, the upper limit value of the indicated current is equal to the maximum value Imax.
Is determined (step 8), and the maximum value Imax
If not, the process returns to step 7. If the upper limit value of the indicated current reaches the maximum value Imax, it is determined whether or not to end the control (step 9), and if not, the process returns to step 1. The end of the control is determined based on, for example, whether or not an ignition key switch of the vehicle is off.

When the control of the motor 10 is performed,
An energization cutoff control procedure performed when an energization cutoff operation is performed by turning off an ignition key switch of the vehicle will be described with reference to a flowchart of FIG. This energization cutoff control may be performed in parallel with the control of the motor 10, or may be alternately interrupted at predetermined intervals. First, when an energization cutoff operation is performed based on an input of an energization cutoff signal by an OFF operation of an ignition key switch (Step 101), a set time elapse signal is output after a predetermined set time has elapsed since the energization cutoff operation was performed. Then, a timer to be turned on is turned on (step 102). The set time is set in advance based on the time required to lower the motor 10 to a temperature at which there is no possibility of overheating at the time of restart after the power supply to the control device 23 is cut off, and is stored in the control device 23, for example, one minute. It is said. Next, the motor 1
It is determined whether or not the upper limit value of the command current to 0 is the maximum value Imax (step 103). If the upper limit of the command current is not the maximum value, it is determined that the upper limit of the command current to the motor 10 is being limited. This allows
It is possible to reliably determine whether or not the upper limit of the instruction current to the motor 10 is being limited. In step 103, if the upper limit value of the command current to the motor 10 is the maximum value Imax, the upper limit value of the command current to the motor 10 is not limited at the time of the power cutoff operation. It shuts off and ends the control (step 104). In step 103, if the upper limit value of the command current to the motor 10 is not the maximum value Imax, it is determined whether or not the ambient temperature T of the motor 10 detected by the temperature sensor 26 is lower than the set temperature To (step 105). The set temperature To is set in advance based on a temperature at which the motor 10 is not likely to be overheated at the time of restart after the power supply to the control device 23 is cut off, stored in the control device 23, and is set to, for example, 55 ° C. If the detected ambient temperature T of the motor 10 is lower than the set temperature To in step 105, that is, if the power cutoff operation to the control device 23 is performed while the upper limit value of the command current to the motor 10 is being limited, The ambient temperature T detected by the sensor 26 is equal to the set temperature T
If it is less than o, the power supply to the control device 23 is cut off and the control is terminated (step 104). If the ambient temperature T of the motor 10 detected by the temperature sensor 26 in step 105 is equal to or higher than the set temperature To, it is determined in advance whether or not the set time has elapsed, that is, the elapsed time since the power-off operation has been performed. It is determined based on a signal from the timer whether or not the value is equal to or greater than the set value (step 106). If the set time has elapsed in step 106, that is, when the power supply cutoff operation to the control device 23 is performed while the upper limit value of the command current to the motor 10 is being limited, the elapsed time is equal to or longer than the set value. If this is the case, the power supply to the control device 23 is cut off and the control is terminated (step 104). If the set time has not elapsed, the process returns to step 101.

According to the above configuration, when the power supply is cut off by turning off the ignition key switch while the upper limit value of the command current to the steering assist force generating motor 10 is being limited, the temperature sensor 26 detects the current. By determining whether or not the measured ambient temperature T is less than a predetermined set value To, and by determining whether or not the elapsed time after the power-off operation is performed is equal to or more than a predetermined set value. It can be determined whether or not the motor 10 has been sufficiently cooled so as not to overheat after the restart. As a result, the power supply to the control device is cut off as soon as possible without causing the motor 10 to overheat after the restart,
Unnecessary increase in power consumption can be prevented. Further, according to the above-described embodiment, when the upper limit of the command current to the motor 10 is limited to prevent overload, the limit can be relaxed according to the ambient temperature. As a result, the command current is prevented from being excessively limited, and a decrease in steering feeling can be suppressed.

The present invention is not limited to the above embodiment. For example, when the power supply cutoff operation is performed while the upper limit value of the command current to the steering assist force generation motor 10 is being limited, in the above embodiment, the ambient temperature T detected by the temperature sensor 26 becomes a predetermined set value. Both the determination as to whether the time is less than To and the determination as to whether or not the elapsed time since the power-off operation was performed are equal to or greater than a predetermined set value are performed. Accordingly, it may be determined whether to cut off the power supply to the control device.

[0028]

According to the present invention, when the power supply cutoff operation is performed during the control for limiting the command current to the motor for generating the steering assist force to prevent the overload, the motor overheats after the restart. An electric power steering device can be provided which cuts off the power supply to the control device as soon as possible without causing the occurrence of the power consumption and prevents the power consumption from increasing more than necessary.

[Brief description of the drawings]

FIG. 1 is a configuration explanatory diagram of an electric power steering device according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a limiting condition stored in a control device in the electric power steering device according to the embodiment of the present invention.

FIG. 3 is an example of a relationship between a set value of a continuous driving time of the motor and an upper limit value of the instruction current to the motor at the start of the limitation of the upper limit value of the instruction current to the motor in the electric power steering apparatus according to the embodiment of the present invention. Figure showing

FIG. 4 is a diagram illustrating an example of a relationship between an integrated value of a current supplied to a motor and an upper limit of a command current to the motor in the electric power steering device according to the embodiment of the present invention;

FIG. 5 is a diagram showing an example of the relationship between the upper limit of the command current and the time when the upper limit of the command current to the motor is gradually increased in the electric power steering device according to the embodiment of the present invention.

FIG. 6 is a flowchart showing a control procedure of a motor in the electric power steering device according to the embodiment of the present invention.

FIG. 7 is a flowchart showing a power cutoff control procedure in the electric power steering device according to the embodiment of the present invention.

[Explanation of symbols]

 10 electric motor 23 controller 26 temperature sensor

Claims (4)

[Claims] An electric power steering apparatus comprising a control device for limiting an upper limit value of a command current to an electric motor for generating a steering assist force in accordance with a preset restriction condition, a temperature for detecting an ambient temperature of the electric motor. A sensor and means for judging whether or not the detected ambient temperature is lower than a predetermined set value are provided, and power is supplied to the control device while the upper limit of the instruction current to the electric motor is being limited. If the detected ambient temperature is lower than the set value when the shutoff operation is performed, the power supply to the control device is shut off. 2. An electric power steering apparatus comprising a control device for limiting an upper limit value of a command current to an electric motor for generating a steering assist force in accordance with a preset restriction condition, the operation of turning off the power supply to the control device is performed. Means is provided for determining whether or not the elapsed time since the start of the operation is equal to or greater than a predetermined set value. Sometimes, if the elapsed time is equal to or greater than a set value, the power supply to the control device is cut off. A temperature sensor for detecting an ambient temperature of the electric motor; and means for judging whether or not the detected ambient temperature exceeds a predetermined set value. When the power supply cutoff operation to the control device is performed in the middle of limiting the upper limit value of the current, if the detected ambient temperature is less than the set value, the power supply to the control device is cut off. 3. The electric power steering device according to 2. 4. As the limiting conditions, the reference current corresponding to the integrated value of the current supplied to the electric motor at the start of the limiting, the minimum value of the upper limit of the indicated current, and the upper limit of the indicated current are reduced. After that, the increase speed when increasing to the maximum value is set in advance, and when the integrated value of the supplied current exceeds the square value of the reference current, the reduction of the upper limit value of the indicated current from the maximum value is started, and When the integrated value of the energizing current exceeds the square value of the minimum value of the upper limit value of the instruction current, the upper limit value of the instruction current is set to the minimum value, and thereafter, the reference current is increased to the maximum value at the increasing speed. Is increased as the set atmosphere temperature is lower, the minimum value of the upper limit value of the indicated current is increased as the set atmosphere temperature is lower, and the increasing speed is lower as the set atmosphere temperature is lower. Fast enough The electric power steering apparatus according to any one among claims 1 to 3 that.