JP2012206674A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device which can always assist control to the safe side and keeps a noise resistance improved by eliminating the influence of the noise which simultaneously varies both torque detection values.SOLUTION: In the electric power steering device, a first torque sensor and a second torque sensor that mutually independently detect the steering torque of the steering device of a vehicle as a first torque detection voltage value (Vt1) and a second torque detection voltage value (Vt2) which pass through a common neutral voltage value (Vn) and are set to mutually antiphase. A steering torque arithmetic means includes a reverse voltage conversion means for converting the second torque detection voltage value (Vt2) to a second torque reverse voltage value (-Vt2) in which plus and minus in voltage are reversed, an average voltage value arithmetic means for calculating the average voltage value (Va) of the first torque detection voltage value (Vt1) and the second torque reverse voltage value (-Vt2) converted by the reverse voltage conversion means, and a neutral voltage value summation means for calculating the steering torque voltage value (Vt) by adding the common neutral voltage value (Vn) to the average voltage value (Va) calculated by the average voltage value arithmetic means.

Description

  The present invention relates to an electric power steering device that assists a driver's steering force, and more particularly to control of steering torque.

  When multiple torque sensors detect the steering torque of the steering system and the difference between the detected values of each torque sensor occurs, the assist control of the steering force by the electric motor is not performed. There is an example in which a fail-safe function is provided (see, for example, Patent Document 1).

However, when it takes time to determine the abnormality by comparing the detection values of the torque sensors, the assist control is performed by the abnormal torque sensor during that time, and a problem may occur.
Further, if the failure determination time is shortened, there is a possibility that an erroneous determination is made when noise or the like is temporarily mixed in one torque sensor.

In view of this, an electric power steering apparatus has been proposed in which an average value of detection values of a plurality of torque sensors is obtained and assist control is performed based on the average value (see, for example, Patent Document 2).
In Patent Document 2, when one torque sensor fails and its detected value shifts to a higher or lower value, it is always safe to perform assist control using the average value of the detected values of both torque sensors. Therefore, the influence of the failure is halved, the failure determination time may be long, and the erroneous determination of the failure with respect to noise or the like can be prevented.

Japanese Utility Model Publication No. 62-152880 Japanese Patent No. 2983714

  However, for the peculiar noise in which the detection values of a plurality of torque sensors such as power supply voltage fluctuations fluctuate in the same direction at the same time, the average value of the plurality of torque detection values as in Patent Document 2 is calculated. The variation of the detected value remains as it is and affects the assist control, and the influence of noise such as power supply voltage variation cannot be removed.

  The present invention has been made in view of this point, and the object of the present invention is to always perform assist control to the safe side even if one of the torque sensors fails, and the noise mixed in each torque sensor is based on both torque detection values. The present invention is to provide an electric power steering apparatus that eliminates the influence of noise that fluctuates simultaneously and improves noise resistance.

In order to achieve the above object, the invention according to claim 1
In the electric power steering device in which the assist motor is driven and controlled according to the assist target current value calculated by the assist target current calculating means based on at least the steering torque, and assists human power.
Steering torque of a vehicle steering system is detected independently as a first torque detection voltage value (Vt1) and a second torque detection voltage value (Vt2) that are set in opposite phases through a common neutral voltage value (Vn). A first torque sensor and a second torque sensor,
Steering torque calculation means for calculating a steering torque voltage value (Vt) input to the assist target current calculation means based on the first torque detection voltage value (Vt1) and the second torque detection voltage value (Vt2). ,
The steering torque calculating means includes
Reverse voltage conversion means for converting the second torque detection voltage value (Vt2) into a second torque reverse voltage value (-Vt2) obtained by reversing the polarity of the voltage;
Average voltage value calculation means for calculating an average voltage value (Va) between the first torque detection voltage value (Vt1) and the second torque reverse voltage value (−Vt2) converted by the reverse voltage conversion means;
It comprises neutral voltage value addition means for calculating the steering torque voltage value (Vt) by adding the neutral voltage value (Vn) to the average voltage value (Va) calculated by the average voltage value calculation means. This is an electric power steering device.

  According to the electric power steering apparatus of the first aspect, the first torque sensor and the second torque sensor set the steering torque of the vehicle steering system in opposite phases through a common neutral voltage value (Vn). The first torque detection voltage value (Vt1) and the second torque detection voltage value (Vt2) are detected independently of each other, and the second torque detection voltage value (Vt2) is reversed by the reverse voltage conversion means. Convert to the second torque reverse voltage value (-Vt2), and calculate the average voltage value (Va) between the first torque detection voltage value (Vt1) and the second torque reverse voltage value (-Vt2) by the average voltage value calculation means The steering torque voltage value (Vt) is calculated by adding the neutral voltage value (Vn) to the average voltage value (Va) by the neutral voltage value addition means, so both torques are detected in the steering torque voltage value (Vt). Fluctuations due to noise that fluctuates simultaneously are removed at the average voltage calculation stage to assist control. It does not affect the.

Since the average voltage value is obtained, assist control can always be performed to the safe side even if one of the torque sensors fails.
Since assist control can always be performed on the safe side, necessary and sufficient failure determination time can be secured, and erroneous determination due to noise mixed in each torque sensor can be prevented.

It is a mimetic diagram for explaining an outline of an electric power steering device. It is a schematic block diagram of the motor control system of ECU. It is a block diagram of the configuration of the steering torque calculation means. It is a rectangular coordinate which shows the relationship of the 1st, 2nd torque detection voltage value with respect to steering torque.

Hereinafter, an embodiment according to the present invention will be described with reference to FIGS.
FIG. 1 is a schematic diagram for explaining the outline of the electric power steering apparatus 10.
The steering shaft 2 extending from the steering wheel 1 is configured by connecting the input side shaft 2a and the output side shaft 2b by a torsion bar 3 in the middle, and the pinion 4 fitted to the end of the output side shaft 2b has a vehicle body width. It meshes with the rack shaft 5 oriented in the direction.

Tie rods 7 and 7 are connected to both ends of the rack shaft 5 via ball joints 6 and 6, respectively.
The tie rod 7 is connected to a steered wheel via a link mechanism (not shown).
Therefore, the steering operation of the steering wheel 1 rotates the pinion 4 via the steering shaft 2, moves the rack shaft 5 meshing with the pinion 4 in either the left or right direction, drives the tie rod 7, and steers the steered wheels.

The electric power steering device 10 is incorporated in the steering mechanism as described above.
The driving force of the assist motor 11 that gives the assist steering force is transmitted to the ball screw mechanism 13 fitted to the rack shaft 5 via the speed reduction mechanism 12, and the right and left width of the rack shaft 5 is actuated by the operation of the ball screw mechanism 13. Assist in moving the direction.
Note that the speed reduction mechanism is not limited to rack assist, and can be used for column, pinion assist, and the like.

The assist motor 11 is driven and controlled by an ECU (electronic control unit) 20, and the motor drive circuit 14 drives the assist motor 11 based on an assist base current Ib output from the ECU 20.
The ECU 20 is controlled by inputting two detection signals from two torque sensors, a first torque sensor 15 and a second torque sensor 16 for detecting steering torque of the steering system.

The first torque sensor 15 and the second torque sensor 16 detect the torsion amount of the torsion bar 3 interposed in the middle of the steering shaft 2 as a steering torque independently of each other.
There are various methods for detecting the torsion amount of the torsion bar 3. For example, the twist of the torsion bar 3 is converted into the axial movement of the core, and the movement of the core is detected by changing the inductance of the coil. A magnet and a Hall IC are arranged opposite to the side shaft 2a and the output side shaft 2b, and a relative deviation (twist angle) between them can be detected as a voltage signal of the Hall IC.

  Each of the first torque sensor 15 and the second torque sensor 16 outputs a voltage value proportional to the steering torque. However, the first torque sensor 15 and the second torque sensor 16 pass through a common neutral voltage value Vn and the first torque detection voltage value Vt1 set in opposite phases. The second torque detection voltage value Vt2 is output.

The relationship between the first torque detection voltage value Vt1 and the second torque detection voltage value Vt2 with respect to the steering torque is shown in the rectangular coordinates of FIG.
The horizontal axis indicates the steering torque, where the origin 0 is the neutral point, the right side is the right steering torque, and the left side is the left steering torque.
On the other hand, the vertical axis represents voltage, with the upper side being a positive voltage and the lower side being a negative voltage.

  The first torque detection voltage value Vt1 is inclined upwards through the neutral voltage value Vn, whereas the second torque detection voltage value Vt2 is inclined downwards through the neutral voltage value Vn. The first torque detection voltage value Vt1 is set to have an opposite phase.

  An outline of the motor control system of the ECU 20 that controls the assist motor M by inputting the first torque detection voltage value Vt1 and the second torque detection voltage value Vt2 which are detected steering torques of the first torque sensor 15 and the second torque sensor 16. A block diagram is shown in FIG.

  The ECU 20 includes steering torque calculation means 21, assist target current calculation means 22, and current feedback control means 23. The first torque detection voltage value Vt1 and the second torque detection voltage value Vt2 are input to the steering torque calculation means 21. The steering torque voltage value Vt is calculated by performing arithmetic processing to be described later and output to the assist target current calculating means 22.

  The assist target current calculation means 22 inputs the vehicle speed v detected by the vehicle speed sensor 17 together with the steering torque voltage value Vt, and calculates and outputs the assist target current Io based on the steering torque voltage value Vt and the vehicle speed v.

  The assist target current Io is a target current for driving the assist motor 11. The larger the steering torque (steering torque voltage value Vt) is, the larger the assist target current Io is, so that the burden on the steering person is reduced. The steering wheel becomes heavier when the vehicle speed is low than when the vehicle speed is high, even if the same steering torque is calculated. Therefore, the assist target current Io is increased to reduce the steering torque.

The assist target current calculation means 22 calculates an appropriate assist target current Io in consideration of the above from the steering torque voltage value Vt and the vehicle speed v.
For example, an optimum relationship of the assist target current Io with respect to the steering torque is determined in advance for each predetermined vehicle speed, and the assist target current Io is calculated from the steering torque voltage value Vt and the vehicle speed v based on the relationship.
Further, the assist target current Io may be obtained by adding a calculation for compensating the inertia torque of the steering system and the inertia torque of the motor.

The assist target current Io is input to the current feedback control means 23, and a drive current Id for controlling the difference between the assist target current Io and the fed back motor current Im to 0 is calculated and output to the motor drive circuit 14. Then, the assist motor 11 is driven by the PWM control of the motor drive circuit 14.
The motor current Im is detected by a motor current detector 18 provided in the assist motor 11.

The steering torque calculation means 21 for calculating the steering torque voltage value Vt from the first torque detection voltage value Vt1 and the second torque detection voltage value Vt2 has a configuration as shown in FIG.
That is, the steering torque calculating means 21 includes a reverse voltage converting means 31, an average voltage value calculating means 32, and a neutral point voltage adding means 33.

The reverse voltage conversion means 31 converts the second torque detection voltage value Vt2 into a second torque reverse voltage value −Vt2 obtained by reversing the polarity of the voltage.
The average voltage value calculation means 32 calculates an average voltage value Va between the first torque detection voltage value Vt1 and the second torque reverse voltage value −Vt2 converted by the reverse voltage conversion means 31.
That is, Va = (Vt1 + (-Vt2)) / 2.

Then, the neutral point voltage addition means 33 calculates the final steering torque voltage value Vt by adding the neutral voltage value Vn to the average voltage value Va calculated by the average voltage value calculation means 32.
That is,
Vt = Va + Vn = (Vt1 + (-Vt2)) / 2 + Vn
It becomes.

Now, referring to FIG. 4, the torque on the horizontal axis is a torque value T with the right side from the origin 0 being a positive value, the slope of the first torque detection voltage value Vt1 is a, and the first torque detection voltage value Vt1 is When expressed by a linear expression, Vt1 = a · T + Vn.
Similarly, the second torque detection voltage value Vt2 is expressed as Vt2 = −a · T + Vn.
Therefore, when the steering torque voltage value Vt is calculated from the previous equation, the steering torque voltage value Vt is
Vt = a · T + Vn
It becomes.

This result is the same as the result of calculating the average value with Vt1 in the case of the conventional patent document 2 as Vt2 = a · T + Vn.
However, when noise enters the power supply voltage and fluctuates, that is, when the first torque detection voltage value Vt1 and the second torque detection voltage value Vt2 fluctuate in the same direction at the same time, the variation ΔV is taken into consideration. 1 torque detection voltage value Vt1 and 2nd torque detection voltage value Vt2
Vt1 = a · T + Vn + ΔV
Vt2 = −a · T + Vn + ΔV
Assuming that the steering torque voltage value Vt is calculated from the previous equation, the steering torque voltage value Vt is expressed as follows: Vt = a · T + Vn
Thus, the variation ΔV is removed.

  Therefore, the fluctuation ΔV due to noise that causes both the first torque detection voltage value Vt1 and the second torque detection voltage value Vt2 to fluctuate simultaneously is calculated by the steering torque voltage value Vt removed by the steering torque calculation means 21 as the assist target current calculation. It is output to the means 22 and does not affect the assist control.

  In the case of the conventional patent document 2, Vt = a · T + Vn + ΔV is calculated, and the variation ΔV remains in the steering torque voltage value Vt and affects the assist control, and the present invention eliminates this. is doing.

Further, since the steering torque voltage value Vt of the present invention is obtained as an average voltage, it is possible to always perform assist control to the safe side even if one of the first torque sensor 15 and the second torque sensor 16 breaks down. it can.
Since the assist control can always be performed to the safe side as described above, a necessary and sufficient failure determination time can be secured, and erroneous determination due to noise mixed in either the first torque sensor 15 or the second torque sensor 16 can be prevented.

  As described above, the removal of the noise mixed in either the first torque sensor 15 or the second torque sensor 16 eliminates the influence of noise that fluctuates the torque detection voltage values Vt1 and Vt2 simultaneously. Noise resistance can be improved.

1 ... handle, 2 ... steering shaft, 3 ... torsion bar, 4 ... pinion, 5 ... rack shaft, 6 ... ball joint, 7 ... tie rod,
DESCRIPTION OF SYMBOLS 10 ... Electric power steering apparatus, 11 ... Assist motor, 12 ... Deceleration mechanism, 13 ... Ball screw mechanism, 14 ... Motor drive circuit, 15 ... 1st torque sensor, 16 ... 2nd torque sensor, 17 ... Vehicle speed sensor, 18 ... Motor current detector,
20 ... ECU, 21 ... steering torque calculation means, 22 ... assist target current calculation means, 23 ... current feedback control means,
31 ... Reverse voltage converting means, 32 ... Average voltage value calculating means, 33 ... Neutral point voltage adding means,
Vt1: first torque detection voltage value, Vt2: second torque detection voltage value, -Vt2: second torque reverse voltage value, Va: average voltage value, Vt: steering torque voltage value,
Io: assist target current, Id: drive current, Im: motor current.

Claims (1)

In the electric power steering device in which the assist motor is driven and controlled according to the assist target current value calculated by the assist target current calculating means based on at least the steering torque, and assists human power.
Steering torque of a vehicle steering system is detected independently as a first torque detection voltage value (Vt1) and a second torque detection voltage value (Vt2) that are set in opposite phases through a common neutral voltage value (Vn). A first torque sensor and a second torque sensor,
Steering torque calculation means for calculating a steering torque voltage value (Vt) input to the assist target current calculation means based on the first torque detection voltage value (Vt1) and the second torque detection voltage value (Vt2). ,
The steering torque calculating means includes
Reverse voltage conversion means for converting the second torque detection voltage value (Vt2) into a second torque reverse voltage value (-Vt2) obtained by reversing the polarity of the voltage;
Average voltage value calculation means for calculating an average voltage value (Va) between the first torque detection voltage value (Vt1) and the second torque reverse voltage value (−Vt2) converted by the reverse voltage conversion means;
It comprises neutral voltage value addition means for calculating the steering torque voltage value (Vt) by adding the neutral voltage value (Vn) to the average voltage value (Va) calculated by the average voltage value calculation means. Electric power steering device.

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