JP2002308120A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device capable of generating an optimum steering feeling in which a movement of the center of gravity of vehicle does not give any influence when the center of gravity has shifted at accelerating or decelerating on a flat road or in running up a slope or down a slope. SOLUTION: The electric power steering device is equipped with a G sensor 12 to sense the gravitational acceleration of the vehicle, a means to decide a motor current command value in accordance with the turn of a steering wheel 1, a means to decide a correction factor in accordance with the gravitational acceleration, a means to calculate the corrected motor current command value on the basis of the motor current command value and the correction factor in accordance with the gravitational acceleration sensed by the G sensor 12, and a means to emit a drive signal to a drive circuit 60 of a steering assist motor 6 on the basis of the corrected motor current command value calculated by the calculating means, whereby the steering assist force in accordance with the gravitational acceleration can be obtained.

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 provided with a motor for assisting the operation of a steering mechanism by steering a steering means.

[0002]

2. Description of the Related Art As an electric power steering device, as described in Japanese Patent Application Laid-Open No. Hei 7-186959,
It has a torque sensor for detecting a steering torque applied to the steering means, a vehicle speed sensor for detecting a vehicle speed, a motor for steering assistance, and a calculation unit for calculating an acceleration in a traveling direction of the vehicle from the vehicle speed detected by the vehicle speed sensor. A control unit that outputs a motor current command value to a drive circuit of the motor, and corrects the motor current command value to a small value based on the acceleration calculated by the calculation unit. There is known a configuration in which a strong steering force is made heavier than when the acceleration is zero.

[0003] As described in Japanese Patent Application Laid-Open No. Hei 6-31666, a steering wheel having a steering wheel and a steering shaft having an upper end connected to the steered wheel and a lower end connected to a pinion, a vehicle speed detecting vehicle speed. A sensor, a steering assist motor, and a control unit that has a determination unit that determines a deceleration traveling state of the vehicle based on the vehicle speed detected by the vehicle speed sensor, and that outputs a motor current command value to a drive circuit of the motor. When the determination unit determines that the vehicle is in the decelerating running state, the motor current command value is corrected to be small, so that the steering force does not suddenly decrease even when the vehicle speed suddenly decreases due to sudden braking. Things are known.

By the way, steering of a vehicle is performed against a road surface reaction force applied to a steering wheel (generally, a front wheel).
The magnitude of the road surface reaction force corresponds to the magnitude of the vehicle speed slowdown and the magnitude of the steering angle, respectively. The drive control of the motor is fundamental.

On the basis of this basic principle, the former Japanese Patent Laid-Open No.
The electric power steering apparatus described in Japanese Patent No. 6995 discloses a motor current command value that is corrected to be small based on the acceleration of the vehicle, and the steering force required when the vehicle accelerates and decelerates is emphasized. The electric power steering device described in Japanese Patent Application Laid-Open No. 6-31666 corrects a motor current command value to a small value when it is determined that the vehicle is in a decelerating running state based on the vehicle speed, and suddenly increases the vehicle speed by abrupt braking. The required steering force is weighted when the vehicle speed is lowered. Therefore, when the vehicle decelerates, a good steering assist force can be obtained.

[0006]

However, the vehicle may run not only on a flat road but also on a slope such as a sloping road. On this slope, the vehicle is inclined in the front-rear direction. On the downhill, the center of gravity of the vehicle moves forward, and on the uphill, the center of gravity of the vehicle moves rearward. Therefore, the steering resistance is higher on a down slope than on a flat road, and the steering resistance is lower on an up slope compared to a flat road, and acceleration and deceleration on a flat road, a down slope, and an up slope. The steering assist force sometimes obtained was different, and an optimum steering feeling as a whole could not be obtained.

[0007] An object of the present invention is to provide an electric power steering device capable of coping with the above circumstances.

[0008]

The electric power steering apparatus according to the present invention comprises a steering means, a motor for assisting the operation of a steering mechanism by the steering of the steering means, and a drive circuit for the motor. An electric power steering device having a control unit for controlling, a detection unit for detecting a gravitational acceleration of the vehicle, a unit for determining a motor current command value in accordance with the steering of the steering unit, and a correction coefficient in accordance with the gravitational acceleration. Means for determining a correction motor current command value based on the correction coefficient and the motor current command value according to the gravitational acceleration detected by the detection means,
Means for outputting a drive signal to the drive circuit based on the corrected motor current command value calculated by the means.

In the present invention, a flat road, a downhill road,
The gravitational acceleration of the vehicle at the time of the uphill ramp and acceleration / deceleration is detected, and the motor current command value can be corrected based on the detected gravitational acceleration. A steering assist force according to the actual acceleration at the time of deceleration can be obtained, and an optimum steering feeling that is not affected by the movement of the center of gravity of the vehicle as a whole can be obtained.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings showing the embodiments. FIG. 1 is a longitudinal sectional view of an electric power steering device according to the present invention.

This electric power steering device has a first steering shaft 2 having an upper end connected to a steered wheel 1 for steering and a lower end having a tubular portion, and an upper end inserted into the tubular portion and having an upper end connected to the steering shaft 2. A torsion bar 3 coaxially connected to the upper end of the torsion bar and twisted by the action of the steering torque applied to the steering wheel 1, and a second steering shaft 4 whose lower end is coaxially connected to the lower end of the torsion bar 3. A torque sensor 5 for detecting a steering torque applied to the steered wheels 1 based on a relative rotational displacement of the first and second steering shafts 2 and 4 according to the torsion of the torsion bar 3; Motor 6 for steering assistance driven based on torque
A control unit 7 for controlling a drive circuit 60 of the motor 6,
A reduction gear mechanism 8 having a drive gear 81 such as a worm and a driven gear 82 such as a worm wheel for reducing the rotation and transmitting the rotation to the second steering shaft 4 in conjunction with the rotation of the motor 6.
And a housing 9 in which the torque sensor 5 and the reduction gear mechanism 8 are accommodated. The motor 6 is mounted on the housing 9. The universal joints connected to the steered wheels 1, the steering shafts 2, 4, the torsion bar 3, and the second steering shaft 4 constitute steering means.

The reduction gear mechanism 8 includes the driving gear 81 connected to the output shaft of the motor 6 and a driven gear 82 fitted and fixed at the middle of the second steering shaft 4. The rotation of the output shaft is reduced by the meshing of the driven gear 82 and transmitted to the second steering shaft 4, and transmitted from the second steering shaft 4 via a universal joint to, for example, a rack and pinion type steering mechanism. ing. This steering mechanism has a pinion connected to the second steering shaft 4 via the universal joint, and rack teeth meshing with the pinion, and is disposed at a front portion of the vehicle body so as to be movable in the left-right direction. A rack shaft and knuckle arms connected to both ends of the rack shaft are provided. The rack shaft is moved in both directions to push and pull the knuckle arm and steer a steering wheel supported by the knuckle arm left and right. It is to let.

FIG. 2 is a block diagram of the control unit. An input unit of the control unit 7 using a microprocessor has the torque sensor 5, a vehicle speed detecting unit 10 using a sensor for detecting a vehicle speed of the vehicle, a steering amount (rotation amount) of the steering wheel 1, A steering detecting means 11 using a rotary encoder for detecting a steering direction and a detecting means 12 using a G sensor for detecting the gravitational acceleration of the vehicle are connected, and the driving circuit 60 is connected to an output section. Have been.

The detecting means 12 is provided with a G sensor inside or outside the control unit 7, the housing 9, or the like, or uses a G sensor already incorporated in the vehicle for controlling the attitude of the vehicle. Thus, the gravitational acceleration of the vehicle is detected.

The control section 7 includes means 13 for determining a motor current command value in accordance with the steering of the steering means, conversion means 14 for converting the gravitational acceleration detected by the detection means 12 into an electric signal, and Means 15 for determining a correction coefficient according to the electric signal converted by the conversion means 14, and a correction motor current based on the correction coefficient corresponding to the electric signal of the gravitational acceleration detected by the detection means 12 and the motor current command value. Means 16 for calculating a command value and means 17 for limiting the corrected motor current command value calculated by the means 16 to a maximum value or less and outputting a target drive signal to the drive circuit 60 are provided.

FIG. 3 is a diagram of a steering torque-motor current command value map. The means 13 for determining the motor current command value includes:
The motor current command value is set using a map created in advance according to the steering torque detected by the torque sensor 5. This map selects one of the characteristics created so as to increase the motor current command value in proportion to the increase in the steering torque in accordance with the vehicle speed detected by the vehicle speed detection means 10. It is configured to output a target motor current command value based on the steering torque detected by the torque sensor 5.

FIG. 4 is a diagram of a gravitational acceleration-correction coefficient map. The means 15 for determining the correction coefficient sets the correction coefficient using a gravitational acceleration-correction coefficient map created in advance according to the gravitational acceleration detected by the G sensor. This map shows that when the vehicle is traveling on a flat road and the vehicle is not accelerated or decelerated, the position of the center of gravity of the vehicle hardly changes.
The correction coefficient is set to 1.0, and when the vehicle is traveling on a descending slope and traveling on a flat road, the center of gravity of the vehicle moves forward, and the steering force is reduced when traveling on a flat road and when not decelerating. The correction coefficient is larger than 1.0 and is set to a maximum of 1.2. When the vehicle accelerates on an uphill road and on a flat road, the center of gravity of the vehicle moves backward. Since the vehicle moves and the steering force decreases as compared to running on a flat road and non-acceleration, the correction coefficient is smaller than 1.0 and is set to a minimum of 0.8. Are determined.

In the electric power steering apparatus configured as described above, the control unit 7 starts the control operation in response to the start of the engine, and the steering torque detected by the torque sensor 5 and the vehicle speed detected by the vehicle speed detecting means 10 And the steering amount (rotation amount) and steering direction of the steered wheel 1 detected by the steering detecting means 11 and the gravitational acceleration detected by the detecting means 12. Based on the read vehicle speed, the steering torque shown in FIG.
One characteristic is selected from the motor current command value map, and a target motor current command value is output based on the selected characteristic and the read steering torque.

On the other hand, a correction coefficient is determined from the gravitational acceleration-correction coefficient map of FIG. 4 based on the read gravitational acceleration. In this case, when the vehicle is traveling on a flat road without acceleration or deceleration, that is, when the gravitational acceleration is 0, the correction coefficient is determined to be 1.0. Further, the gravitational acceleration detected when the vehicle is traveling on a downhill slope and when the vehicle is decelerated while traveling on a flat road is determined to be a correction coefficient larger than 1.0. Further, the gravitational acceleration detected when the vehicle is traveling on an uphill or when traveling on a flat road is determined as a correction coefficient smaller than 1.0, and this correction coefficient is output. You.

The product of the output motor current command value and the correction coefficient is calculated by means 16 for calculating, and a target drive signal is output from the means 17 based on the calculated corrected motor current command value. The motor 6 is driven based on the drive signal. In this case, the corrected motor current command value when the vehicle is traveling on a downhill slope and when decelerated during running on a flat road is a higher value than the uncorrected motor current command value, and The corrected motor current command value when the vehicle is traveling on an uphill road and when the vehicle is accelerated on a flat road has a lower value than the uncorrected motor current command value.

As described above, according to the present invention, the motor current command value can be corrected on the basis of the flat road, the downhill, the uphill, and the gravitational acceleration during acceleration / deceleration. It is possible to obtain a steering assist force according to the actual acceleration at the time of the road, the climbing slope, and the acceleration and deceleration, and it is possible to obtain an optimum steering feeling that is not affected by the movement of the center of gravity of the vehicle.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of an electric power steering device according to the present invention.

FIG. 2 is a block diagram of a control unit of the electric power steering device according to the present invention.

FIG. 3 is a diagram of a steering torque-motor current command value map.

FIG. 4 is a diagram of a gravitational acceleration-correction coefficient map.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steering wheel 6 Motor 7 Control part 12 Detecting means 60 Drive circuit

Claims (1)

[Claims] 1. An electric power steering apparatus comprising a steering unit, a motor for assisting the operation of a steering mechanism by the steering of the steering unit, and a control unit for controlling a driving circuit of the motor. Detecting means for detecting
Means for determining a motor current command value in accordance with the steering of the steering means, means for determining a correction coefficient in accordance with the gravitational acceleration, the correction coefficient and the motor current command value in accordance with the gravitational acceleration detected by the detection means And a means for outputting a drive signal to the drive circuit based on the corrected motor current command value calculated by the means. Steering device.