JP3163920B2 - Electric power steering device and control unit used for it - 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 an automobile and a control unit used for the apparatus.

[0002]

2. Description of the Related Art Conventionally, an electric power steering device has
A steering torque is detected by a steering torque sensor attached to the steering shaft of the steering wheel, and a steering assist force is generated by passing a current to a motor that transmits driving force to the steering shaft etc. according to the magnitude of the steering torque. is there. Since the relationship between the steering assist force and the motor current is considered to be linear, the assist characteristic of the steering assist is represented by the relationship between the steering torque and the motor current, as shown in FIG. 5 (showing both sides in the left-right steering direction). . Also, this property
The motor current changes depending on the vehicle speed calculated based on the signal from the vehicle speed sensor, and the motor current increases at a low vehicle speed. For this reason, when an operation requiring a large steering assist force, such as a garage putting operation, is repeated for a long time, a correspondingly large current flows through the motor for a long time, resulting in an increase in the amount of heat generated by the motor and damage to the motor. There is fear. Therefore, as a countermeasure against heat generation of the motor, there is a method of limiting the maximum current of the motor from the average current of the motor (for example, Japanese Patent Application Laid-Open No. 63-263167, Japanese Patent Publication No.
No. 1474).

[0003]

However, according to the method disclosed in the above-mentioned publication, when the average current exceeds a specified value, such as when the stationary / end contact state continues, the maximum current of the motor is reduced. It is limited and the current value drops. Therefore, the average value of the current value decreases, does not exceed the specified value, the restriction on the maximum current of the motor is released, and the current starts flowing through the motor. The relationship between the motor current and the temperature in such a state is as shown in FIG. The motor operation in this stationary / end-contact state, regardless of the driver's operation,
It is controlled only by the motor current value.
When the end contact state is continued, overheating and cooling of the motor are repeatedly performed, and the motor is continuously stressed. The present invention solves the above-mentioned problem, and monitors the steering torque input to limit the current supplied to a motor that generates a steering assist force when the vehicle is considered to be in a garage or end contact. Accordingly, an object of the present invention is to provide an electric power steering device capable of reducing heat generation of a motor and a control unit used for the electric power steering device.

[0004]

In order to achieve the above object, the present invention provides a steering torque sensor for detecting a steering torque of a steering wheel, a motor for generating a force for assisting steering of the steering wheel, and a steering torque. An electric power steering apparatus comprising: a control unit that receives a steering torque signal from a sensor and controls a current supplied to a motor, wherein the control unit calculates an average value of the steering torque from a detection signal from the steering torque sensor. Steering torque average value calculating means, and when the steering torque average value obtained by the steering torque average value calculating means is equal to or more than a predetermined value, regardless of the steering angle or the amount of fluctuation of the steering angle. And current control means for reducing the current flowing through the motor. According to a second aspect of the present invention, in addition to the configuration of the first aspect, a means for detecting a vehicle speed or an engine speed is further provided, and the current control means controls the average value of the steering torque at a low vehicle speed or a low engine speed. Is greater than the specified value,
This is to reduce the current flowing through the motor. According to a third aspect of the present invention, there is provided a steering torque sensor for detecting a steering torque of a steering wheel, a motor for generating a force for assisting steering of the steering wheel, and a current supplied to the motor upon receiving a steering torque signal from the steering torque sensor. An electric power steering device comprising a control unit for controlling
When the control unit maintains the steering torque value equal to or greater than the predetermined value for a predetermined time or more , the steering angle
And a current control means for reducing the current flowing through the motor irrespective of the fluctuation amount of the steering angle . According to a fourth aspect of the present invention, in addition to the configuration of the third aspect, a means for detecting a vehicle speed or an engine speed is further provided, and the current control means sets a value of the steering torque at a low vehicle speed or a low engine speed. When the state equal to or higher than the predetermined value is maintained for a predetermined time or longer, the current flowing to the motor is reduced. According to a fifth aspect of the present invention, there is provided a control unit used in an electric power steering device that assists a steering force by a motor in accordance with a steering torque of a steering wheel, wherein a control signal is obtained from a detection signal of a steering torque detection sensor that detects the steering torque.
A steering torque average value calculating means for calculating an average value of the steering torque ; and a steering angle or steering angle when the steering torque average value obtained by the steering torque average value calculating means is equal to or more than a predetermined value.
Current control means for reducing the current flowing through the motor irrespective of the angle variation . According to a sixth aspect of the present invention, in the configuration according to the fifth aspect, the current control means flows to the motor when the average value of the steering torque exceeds a predetermined value in a state where the vehicle speed is low or the engine speed is low. This is to reduce the current. According to a seventh aspect of the present invention, there is provided a control unit for use in an electric power steering apparatus for assisting a steering force by a motor in accordance with a steering torque of a steering wheel, wherein a state in which the value of the steering torque is a predetermined value or more is maintained for a predetermined time or more. when the lasted over,
A current control means is provided for reducing the current flowing through the motor irrespective of the steering angle and the variation of the steering angle . According to a seventh aspect of the present invention, in the configuration of the seventh aspect,
The current control means reduces the current flowing to the motor when the value of the steering torque is equal to or higher than a predetermined value at a low vehicle speed or a low engine speed for a predetermined time or more.

[0005]

In the electric power steering apparatus having the above structure, the average value calculating means of the control unit calculates an average value of the steering torque from a steering torque detection signal of the steering wheel detected by the steering torque sensor.
When the average value of the steering torque is equal to or more than a predetermined value, the current control means, regardless of the steering angle or the amount of change in the steering angle,
The current flowing to the motor that assists the force required for turning the steering wheel is reduced. By monitoring the steering torque in this manner, when it is determined that the heat generation amount of the motor is large, it is possible to reduce the heat generation of the motor without flowing an extra current. Further, in the electric power steering apparatus according to the second aspect, when the average value of the steering torque becomes equal to or more than a predetermined value in a state where the vehicle speed is low or the engine speed is low, the current control means reduces the current flowing through the motor. This makes it possible to reduce the heat generated by the motor when the steering operation is performed in a garage or end contact. Further, in the electric power steering apparatus according to claim 3, the steering torque sensor detects a steering torque of the steering wheel, and the control unit receives a steering torque signal from the steering torque sensor and assists a motor for assisting a force required for rotating the steering wheel. Control the supplied current. At this time, the current control means of the control unit, when the value of the steering torque is maintained at a predetermined value or more for a predetermined time or more , the steering angle and the fluctuation amount of the steering angle
Irrespective of reducing the current flowing through the motor. Thereby, an operation equivalent to that of the first aspect is obtained. Claim 4
In the electric power steering apparatus, the current control means reduces the current flowing through the motor when the value of the steering torque is equal to or more than a predetermined value for a predetermined time or more at a low vehicle speed or a low engine speed. Thus, an operation equivalent to that of the second aspect is obtained. In the control unit according to claim 5, the steering torque average value calculating means calculates an average value of the steering torque from the detection signal of the steering torque detection sensor, and the current control means determines that the steering torque average value is equal to or more than a predetermined value. At the same time, regardless of the steering angle or the amount of change in the steering angle,
Reduce the current flowing through the motor. Thus, when it is determined that the heat generation amount of the motor is large, it is possible to reduce the heat generation of the motor without flowing an extra current. Further, in the control unit according to claim 6, the current control means reduces the current flowing to the motor when the average value of the steering torque becomes equal to or more than a predetermined value at a low vehicle speed or a low engine speed. Thus, an operation equivalent to that of the fifth aspect is obtained.
Further, in the control unit according to claim 7, when the value of the steering torque is equal to or greater than the predetermined value for a predetermined time or more, the current control means changes the steering angle or the change in the steering angle.
Irrespective of the moving amount, the current flowing through the motor is reduced, and the same operation as described above is obtained. Further, in the control unit according to claim 8, the current control means is configured to control the current flowing through the motor when the steering torque value is maintained at a predetermined value or more for a predetermined time or more at a low vehicle speed or a low engine speed. And an effect equivalent to the above is obtained.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of the electric power steering device. The electric power steering device
The steering wheel 1 includes a steering wheel 1 to which a driver applies a steering torque. The steering wheel 1 is connected to a pinion gear 2 and a rack shaft 3 via a steering shaft 1a.
The operation wheel 4 is connected to. Further, the electric power steering device includes a steering torque sensor 5 for detecting a steering torque applied to the steering wheel 1, a motor 6 for generating an auxiliary driving force necessary for steering the steering wheel 1, and a motor 6.
An auxiliary driving mechanism 7 for applying the auxiliary driving force of
A control device 8 (control unit) that controls the amount of current supplied to the motor 6 based on the steering torque detected by the steering torque sensor 5 is provided. A vehicle speed signal from a vehicle speed sensor 9 is also input to the control device 8, and power is supplied from a battery 10.

FIG. 2 is a specific configuration diagram of the electric power steering device. The control device 8 includes a CPU 21 that controls the entire electric power steering device,
A motor drive circuit 22 controlled by the PU 21 to drive and control the motor 6;
A motor current / voltage detection circuit 23 to be input to 21, a fail safe circuit 24 for limiting the current value when the motor current exceeds a predetermined allowable value, and a power supply to the motor drive circuit 22 for fail safe And a relay circuit 25 and a relay contact 26 for performing / interrupt control. CPU2
1 receives an engine speed signal 27 in addition to the detection signals from the steering torque sensor 5 and the vehicle speed sensor 9. When the ignition key switch 28 is turned on, the relay circuit 25 operates and power is supplied to the motor drive circuit 22. The CPU 21 performs pulse width modulation (PWM) on the motor drive circuit 22 in accordance with the steering torque detected by the steering torque sensor 5, so that the motor 6 generates an assisting force required for steering.
Is controlled.

FIG. 3 is a block diagram of the motor control function executed by the CPU 21. A steering torque 31 which is a detection signal from the steering torque sensor 5 is converted into a motor current value by a steering torque / motor current characteristic 33a of a motor current determination 33, and a vehicle speed 32 which is a detection signal from the vehicle speed sensor 9 is The gain is adjusted in the amplifier 35 by the vehicle speed / gain characteristic 34, and the target current value is determined based on these. As for the steering torque 31, the average value of the steering torque is calculated by the torque average value calculation 36, and the maximum current value is determined by the torque average value / current maximum value characteristic 37. Then, the maximum current value is determined by the current maximum value restriction 38 from the target current value and the current maximum value. The motor current control 39 includes a motor current detection 4
0, the motor current of the motor 6 is detected and P
The feedback control by WM is performed, and the current maximum value limitation 38 acts on the motor current control 39 so as to limit the supply current to the motor 6 to the determined maximum current value. The motor 6 and the motor current detection 40 shown in FIG. 3 include the motor drive circuit 22 and the motor current / voltage detection circuit 23 shown in FIG.

The operation of the electric power steering apparatus configured as described above, in particular, the motor current control will be described with reference to the flowchart of FIG. The ignition key switch 28 of the electric power steering device is turned on
Then, power is supplied to the control device 8 and the CP
U21 performs initial processing such as initial setting of gain (S21).
1) The steering torque is read from the detection signal from the steering torque sensor 5 (S2). Further, the motor current is read by the motor current / voltage detection circuit 23 (S3). Next, a torque average value is calculated from the read steering torque (S4),
This torque average value is the torque average value / current maximum value characteristic 3
7 (S5). If the torque average value is larger than the specified value (YES in S5), a current corresponding to the torque average value is determined. The maximum value is calculated (S6). If the average torque value is not larger than the specified value (NO in S5), a predetermined current maximum value is selected (S7). Subsequently, a target current value is created from the steering torque / motor current characteristic 33a (S
8) It is checked whether this target current value is larger than the current maximum value obtained in S6 or S7 (S9). If the target current value is larger than the current maximum value (YES in S9), the current maximum The target current value is limited by the value limit 38 (S1
0), motor current control is performed by PWM (S11). If the target current value is not larger than the current maximum value (NO in S9), the motor current control is performed by PWM using the target current value as it is (S11). Thereafter, the processing is S
2, the same operation is repeated.

According to the electric power steering apparatus of the present embodiment, by performing the above-described processing, the steering torque is monitored, and when the average value exceeds a specified value, an increase in the motor current can be limited. Thereby, heat generation of the motor 6 can be reduced. Further, by monitoring the torque, it is possible to monitor that the operations such as stationary operation and garage operation are performed irrespective of the motor current value. Therefore, the motor 6 can be monitored by a series of operations such as stationary operation. When it is determined that the heat generation amount is large, the current can be appropriately limited so as not to flow an extra current, and the large current is not repeatedly supplied, so that the motor 6 becomes abnormally high temperature due to heat storage. Can be avoided.

In the above-described flowchart, the process of adjusting the gain of the target current value using the vehicle speed / gain characteristic 34, which is performed in response to the vehicle speed from the vehicle speed sensor 9 shown in FIG. Although the control process using the engine speed signal 27 is not shown, if the vehicle current sensitivity and the engine speed detection are considered together with the value of the steering torque to limit the motor current, the control process is further improved. Precise control becomes possible. That is, when the average value of the steering torque is equal to or more than the predetermined value in a state where the vehicle speed is low or the engine speed is low, the motor current is reduced so that the operations such as the stationary operation and the garage operation are continued. In this case, abnormal heat generation of the motor 6 can be reliably prevented. Further, even if the steering torque is not the average value, it is determined that the steering torque value is abnormal when the steering torque value exceeds a predetermined value for a predetermined time or more, or when it is combined with a low vehicle speed or a low engine speed. If it can be determined, control may be performed to reduce the motor current. As a method of reducing the motor current, in addition to the above-described limitation of the maximum value of the motor current,
A method of limiting the average value of the motor current is also conceivable. In the above flowchart, the method of obtaining the maximum current value and the like by calculation has been described. However, a method using a table instead of the calculation may be used.

[0012]

As described above, according to the electric power steering apparatus or the control unit for the electric power steering apparatus according to the first or fifth aspect of the present invention, when the steering torque average value exceeds a predetermined value , the steering angle or the steering angle can be reduced. Irrespective of the amount of fluctuation , the current flowing through the motor that assists the force required to rotate the steering wheel is reduced, so that the heat generated by the motor can be reduced. Moreover, since the torque is monitored, operations such as stationary and garage can be monitored irrespective of the motor current value. Therefore, when it is determined that the heat generation of the motor is large, an extra motor is required. It is possible to limit the current from flowing, and to prevent the motor from becoming abnormally high temperature. Further, according to the electric power steering apparatus or the control unit thereof according to the invention of claim 2 or 6,
Since the steering torque is monitored at a low vehicle speed or a low engine speed, the above effects can be obtained more accurately. Further, according to the electric power steering apparatus or the control unit thereof according to the invention of claim 3 or 7, when the state where the value of the steering torque is equal to or more than the predetermined value is maintained for a predetermined time or more , the steering angle or the steering angle is adjusted. Fluctuation amount
Irrespective of this, the current flowing to the motor is reduced, so there is an intention to continue the operation when it is determined that the heat generation of the motor is large in a series of operations such as stationary and garage. It is possible to limit the excess motor current from flowing as much as possible, thereby avoiding reaching an abnormal temperature due to heat accumulation in the motor due to repeated flow of a large motor current. Further, according to the electric power steering apparatus or the control unit thereof according to the invention of claim 4 or 8, since the steering torque is monitored at a low vehicle speed or a low engine speed, the above effect is further enhanced. Can be obtained accurately.

[Brief description of the drawings]

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

FIG. 2 is a specific configuration diagram of an electric power steering device.

FIG. 3 is a block diagram illustrating functions of a control device in the electric power steering device.

FIG. 4 is a flowchart showing the operation of the control device.

FIG. 5 is a diagram showing a relationship between a steering torque and a motor current in a conventional electric power steering device.

FIG. 6 is a diagram showing a relationship between motor current and temperature in a conventional electric power steering device.

[Explanation of symbols]

 DESCRIPTION OF REFERENCE NUMERALS 1 steering wheel 5 steering torque sensor 6 motor 8 control device 9 vehicle speed sensor 21 CPU 33a steering torque / motor current characteristic 36 torque average value calculation 37 torque average value / current maximum value characteristic 38 current maximum value limit 39 motor current control

Claims (8)

(57) [Claims] A steering torque sensor for detecting a steering torque of a steering wheel, a motor for generating a force for assisting steering of the steering wheel, and a current supplied to the motor upon receiving a steering torque signal from the steering torque sensor. An electric power steering apparatus comprising: a control unit for controlling the steering unit; wherein the control unit calculates a steering torque average value from a detection signal from the steering torque sensor, and the steering torque average value calculation unit. the is sometimes <br/> steering torque average value obtained is equal to or greater than a predetermined value, regardless of the amount of variation in the steering angle and the steering angle, and a current control means for reducing the current flowing in the motor An electric power steering device characterized by the above-mentioned. 2. The vehicle according to claim 1, further comprising: means for detecting a vehicle speed or an engine speed, wherein the current control means is configured to control the motor control when the average value of the steering torque is equal to or more than a predetermined value at a low vehicle speed or a low engine speed. 2. The electric power steering apparatus according to claim 1, wherein a current flowing through the power steering apparatus is reduced. 3. A steering torque sensor for detecting a steering torque of a steering wheel, a motor for generating a force for assisting steering of the steering wheel, and a current supplied to the motor upon receiving a steering torque signal from the steering torque sensor. An electric power steering apparatus comprising: a control unit that controls the control unit, wherein the control unit is configured to control when the value of the steering torque is equal to or greater than a predetermined value for a predetermined time or more.
An electric power steering apparatus comprising: a current control unit that reduces a current flowing through the motor irrespective of a steering angle and a variation amount of the steering angle . 4. A means for detecting a vehicle speed or an engine speed, wherein the current control means changes the steering torque value to a predetermined value or more at a low vehicle speed or a low engine speed for a predetermined time or more. The electric power steering apparatus according to claim 3, wherein the current flowing through the motor is reduced when the electric power steering is continued. 5. A control unit for use in an electric power steering apparatus for assisting a steering force by a motor in accordance with a steering torque of a steering wheel, wherein an average value of the steering torque is obtained from a detection signal of a steering torque detection sensor for detecting the steering torque. And a steering angle or steering angle when the steering torque average value obtained by the steering torque average value calculation means is equal to or greater than a predetermined value.
A current control means for reducing a current flowing through the motor irrespective of a variation amount of the control unit. 6. The motor according to claim 1, wherein the current control means reduces a current flowing through the motor when an average value of the steering torque becomes equal to or more than a predetermined value in a state of low vehicle speed or low engine speed. Item 6. The control unit according to Item 5. 7. A control unit for use in an electric power steering apparatus for assisting a steering force by a motor in accordance with a steering torque of a steering wheel, wherein the value of the steering torque is maintained at a predetermined value or more for a predetermined time or more. sometimes, the amount of variation in the steering angle and the steering angle
Irrespective of this, a control unit comprising a current control means for reducing a current flowing through the motor. 8. The current control means reduces a current flowing through the motor when a value of the steering torque is equal to or greater than a predetermined value for a predetermined time or more at a low vehicle speed or a low engine speed. 8. The method according to claim 7, wherein
Control unit as described.