JP2012076657A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem that a bilateral difference in steering wheel return characteristics occurs as a consequence of a bilateral difference in friction in a rotational direction of each part of a steering device and a vehicle according to a steering rotational direction when returning a steering wheel and a great unbalance occurs in return torque feeling, return speed and return angle between returns from steering to the right and left.SOLUTION: An electric power steering device includes a memory 88 for storing, according to a determined rotational direction of an electric motor, steering torque when a motor rotation speed comes to correspond to an idling speed; and a rotation torque bilateral difference adjustment unit 87 for adjusting a bilateral torque difference using a ratio of the steering torque in the rotational direction of each electric motor stored in the memory 88 to a preset value of rotation torque as a coefficient for torque corresponding to a road surface reaction force of a tire received from a road surface by a tire. Steering wheel return control is performed by subtracting the torque corresponding to the road surface reaction force adjusted by the rotation torque bilateral difference adjustment unit 87 from assist torque determined by a basic assist control unit 71.

Description

  The present invention relates to an electric power steering apparatus mounted on a vehicle, and more particularly to an electric power steering apparatus capable of controlling the direction and magnitude of assist torque generated by the electric power steering apparatus when the steering wheel is returned.

The electric power steering device detects a steering torque generated when the driver operates the steering wheel, and applies a current corresponding to the vehicle speed and the detected value of the steering torque to the electric motor for rotational driving. Since the electric motor meshes with the mechanism of the electric power steering device, the necessary assist torque can be generated by applying this current.
In general, the electric power steering apparatus has a self-aligning function. That is, in the process of returning to the straight traveling state after turning, if the driver turns the force for rotating the steering wheel to 0 (so-called hand-off state), the wheel automatically attempts to return to the neutral position.

However, in the conventional electric power steering device, even when the wheel tries to return to the neutral position direction due to the self-aligning function, the frictional force corresponding to the friction of the rotor of the electric motor and the vehicle and the steering system etc. In some cases, the driver did not return completely, and the driver re-rotated the steering wheel in the straight direction.
As a method for partially solving this problem, a method for improving the handle return has been proposed. This method generates assist torque in the same direction (return direction) as the rotation direction of the electric motor according to the rotation speed or rotation acceleration of the electric motor if the rotation direction of the motor and the direction of the steering torque are different. Then, a current corresponding to the generated assist torque is supplied to the electric motor for rotation.

JP-A-7-186994 JP 2002-29442 A

  The above configuration can be expected to improve the return of the steering wheel when it is released at low vehicle speeds, but the steering wheel return characteristics are affected by the difference in the left and right friction in each part of the steering system and the rotational direction of the vehicle. There was a drawback that left and right difference would occur. As a result, if the self-aligning function causes the wheels to return to the neutral position, the imbalance between the characteristics of the return torque feeling, speed, and return angle from the right and left steering will occur. was there.

  The object of the present invention is to actually measure and store the difference in left and right friction during steering of the rotor of the electric motor, the vehicle, and the steering system, and to correct the return force and the friction imbalance due to the return direction of the steering wheel. By correcting the correction amount to an appropriate value in accordance with each direction, it is possible to eliminate the left-right difference in the steering wheel return characteristic.

  The electric power steering apparatus according to the present invention includes a steering torque detecting means for detecting a steering torque generated by the driver rotating the steering, and a steering torque by the driver based on the steering torque detected by the steering torque detecting means. Basic assist control means for determining assist torque for assisting the motor, motor rotation speed detection means for detecting the rotation speed of the electric motor for generating the assist torque, and motor rotation direction determination means for determining the rotation direction of the electric motor And the steering torque when the motor rotational speed is equivalent to the no-load rotational speed based on the motor rotational speed signal from the motor rotational speed detecting means and the steering torque signal from the steering torque detecting means, Storage means for storing each rotation direction of the electric motor determined by the determination means; With respect to the torque corresponding to the road surface reaction force of the tire that the tire receives from the road surface, the ratio of the steering torque in the rotational direction of each electric motor stored in the storage means with respect to the predetermined value of the rotational torque is used as a coefficient. Torque left and right difference adjusting means for adjusting, by subtracting the torque corresponding to the road surface reaction force adjusted by the torque left and right difference adjusting means from the assist torque determined by the basic assist control means, Handle return control is performed.

  The steering torque when the motor rotational speed is equivalent to the no-load rotational speed is considered to directly represent the friction torque of the rack and pinion in the steering mechanism, the mechanism portion that moves in conjunction with the steering of the vehicle, and other vehicles. Therefore, the direction of which direction of friction is to be corrected is determined, this friction torque is stored in the storage means for each direction, and a correction coefficient is added to the steering assist torque signal according to the direction of the friction to be corrected. Multiply and output. As a result, the left-right difference in the handle return characteristic can be eliminated.

  Generally, the friction torque value of the mechanism part that moves in conjunction with the rack and pinion in the steering mechanism or the steering of the vehicle varies depending on the steering direction of the steering wheel. If the friction value is large, each rotation depends on the rotation direction of the steering. Although the difference in the magnitude of the friction in the direction tends to increase, the control according to the present invention can appropriately compensate for each different friction depending on the rotation direction.

If the motor rotation direction determination means determines the rotation direction of the electric motor M based on the terminal voltage of the electric motor M, it is not necessary to monitor the steering wheel direction with the steering angle sensor.
The torque corresponding to the road surface reaction force of the tire can be estimated based on the electric motor current flowing in the electric motor and the steering torque detected by the steering torque detecting means.

  As described above, according to the present invention, the difference in the vehicle friction in the rotation direction is learned, and the return force and the friction imbalance that differ depending on the return direction of the steering wheel are adjusted to the respective directions according to the learning result. By adjusting to an appropriate value, the effect of automatically eliminating the left-right difference in the handle return characteristics can be obtained.

It is a block diagram for demonstrating the structural example of an electric power steering device. It is a graph which shows the value of the correction coefficient according to rotation direction.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a block diagram for explaining a configuration example of an electric power steering apparatus. This electric power steering device is used by being mounted on a vehicle, and drives an electric motor M (for example, a brushless electric motor) in accordance with an operation of a steering handle 51 as an operation member, and assist torque generated by the electric motor M. Is mechanically transmitted to the steering mechanism 52 to assist steering.

  The electric power steering apparatus includes a torque sensor 53 that detects a steering torque applied to the steering handle 51, and an electric power steering ECU (electronic control unit) as a controller. The ECU is further provided with an output signal of a vehicle speed sensor 54 that detects the speed (vehicle speed) of the vehicle, and an output signal of a rotation angle sensor 55 such as a rotary encoder that detects the rotation angle of the electric motor M. It has been. The ECU drives and controls the electric motor M based on signals from the torque sensor 53, the vehicle speed sensor 54, and the rotation angle sensor 55.

The ECU includes a microcomputer 60 and a current detection circuit 58, a PWM (pulse width modulation) pulse generation circuit 56, and an electric motor drive circuit 57.
The microcomputer 60 generates a control signal for controlling the electric motor M based on the steering torque, the vehicle speed, and the rotation angle of the electric motor M, and supplies the control signal to the PWM pulse generation circuit 56. The PWM pulse generation circuit 56 generates a PWM pulse having a duty corresponding to the given control signal and inputs the PWM pulse to the electric motor drive circuit 57. The electric motor drive circuit 57 includes a plurality of switching elements that are turned on / off based on the PWM pulse supplied from the PWM pulse generation circuit 56, and supplies a current corresponding to the control signal to the electric motor M. The current actually flowing through the electric motor M is detected by the current detection circuit 58, and the detection result is input to the microcomputer 60.

  The microcomputer 60 substantially has a plurality of function processing units realized by a CPU (not shown) executing a predetermined program stored in an internal memory (not shown). The plurality of function processing units include a steering torque calculation unit 61 that calculates the steering torque by processing the input signal from the torque sensor 53, and a vehicle speed calculation unit that calculates the vehicle speed by processing the input signal from the vehicle speed sensor 54. 63, a motor rotation speed calculation unit 65 for processing the input signal from the rotation angle sensor 55 to calculate the rotation speed of the electric motor M, and the output of the motor rotation speed calculation unit 65 is time-differentiated to obtain the rotation acceleration. A motor rotation acceleration calculating unit 66 for calculating is included. For example, the motor rotation speed calculation unit 65 may obtain the rotation speed by subtracting the pulse output of the rotary encoder.

  Further, the plurality of function processing units include a basic assist control unit 71 and a handle return control unit 73. Then, the steering wheel return control current obtained by the steering wheel return control unit 73 is subtracted from the current command value obtained by the basic assist control unit 71, and the current value after this subtraction and the output signal of the current detection circuit 58 are motorized. The actual electric motor current value obtained by processing by the motor current calculation unit 68 is supplied to the electric motor current control unit 69. The electric motor current control unit 69 obtains a deviation between the final current command value and the actual electric motor current value, and outputs a control signal for making the current value of the electric motor M coincide with the final current command value. To give.

  The basic assist control unit 71 generates a basic assist current value based on the steering torque calculated by the steering torque calculation unit 61 and the vehicle speed calculated by the vehicle speed calculation unit 63. Specifically, a calculation is performed to determine a basic assist current value so that a larger assist current value is generated as the steering torque is larger, and a smaller assist current value is generated as the vehicle speed is higher (during high-speed driving). .

  The steering wheel return control unit 73 moves the steering handle 51 to the neutral position based on the steering torque calculated by the steering torque calculation unit 61, the vehicle speed calculated by the vehicle speed calculation unit 63, and the electric motor current calculated by the electric motor current calculation unit 68. This is a portion that generates a handle return control current so that the electric motor M generates torque in a direction to return the handle to the origin when returning to the initial position.

  The steering wheel return control unit 73 adds the steering motor-converted electric motor torque calculated from the electric motor current calculation unit 68 to the steering torque output from the steering torque calculation unit 61, thereby adjusting the steering angle of the front wheels. Based on the road surface reaction force torque estimation unit 81 that estimates the road surface reaction force torque to be returned to the origin, and the motor rotation acceleration output from the steering torque and motor rotation acceleration calculation unit 66, the mass of the steering handle 51, An inertial force compensator 82 for calculating a compensation torque for compensating an inertial force generated by the inertia of the rotor of the electric motor M, and a first adder 83 for adding the road surface reaction force torque and the inertial force compensation torque. It has. Note that the road surface reaction force torque and the inertial force compensation torque in the steering wheel return control unit 73 are torques converted to the rack output shaft of the steering mechanism 52.

  Further, the steering wheel return control unit 73 includes a gain generation unit 84 and a limiting unit 85 that convert the torque output from the first adder 83 into a current and multiply it by a proportional gain A. By multiplying the proportional gain A, the torque for returning the handle to the origin can be made smaller than the road surface reaction torque. Therefore, since the straight traveling property of the vehicle can be promoted, the steering wheel return performance of the vehicle can be improved. Note that the proportional gain A can be changed according to the vehicle speed so that the gain A decreases as the vehicle speed increases and the gain A increases as the vehicle speed decreases. In order to avoid a phenomenon in which the steering wheel does not automatically return to the origin when the road surface reaction torque is smaller than the friction torque in the steering mechanism 52, the restricting unit 85 transmits a steering wheel return assist torque signal to approximately the friction torque in the steering mechanism. Limit by the limiter with the value of. This limit value can also be changed according to the vehicle speed.

  Furthermore, the steering wheel return control unit 73 is configured to perform vehicle friction (rotation of the rotor of the electric motor M) based on the steering torque calculated by the steering torque calculation unit 61 and the motor rotation speed calculated by the motor rotation speed calculation unit 65. Friction that occurs in the entire vehicle including friction and friction of the steering system of the steering mechanism 52. The same applies to the following, and a learning unit 86 that learns the difference in steering torque for each motor rotation direction and the output of the learning unit 86 And a rotational torque left / right difference adjustment unit 87 that adjusts the difference in vehicle friction direction to be zero depending on the left / right rotational direction.

  The learning unit 86 determines the rotation direction of the electric motor M based on the terminal voltage of the electric motor M, and stores the steering torque when the motor rotation speed corresponds to the no-load rotation number in the memory 88. The no-load rotation speed is a standard value of the electric motor M, and is a rotation speed (for example, 2000 rpm) at which the electric motor M rotates when a predetermined voltage (for example, 12 V) is applied without applying torque to the electric motor M. is there. The no-load speed appears when the steering wheel is quickly turned off while driving, or when the steering wheel is turned off quickly after jacking up the vehicle body. The steering torque at the no-load speed represents the vehicle friction as it is. A ratio (correction coefficient) of the obtained steering torque to a prescribed value of the steering torque is stored for each rotation direction of the electric motor M. For example, if the specified value of the steering torque is 1.0 Nm, the correction coefficient is 1.3 if the steering torque measurement result is 1.3 Nm in the left rotation direction. If the rotation direction is 1.0 Nm, the correction coefficient is 1.0. The values of these correction coefficients for each rotation direction are shown in FIG. Thus, for example, if the friction at the time of the right steering rotation on the handle shaft is 30% larger than that at the left steering rotation, the correction coefficient can be set so that the steering wheel return assist torque signal when returning by the right rotation is increased by 30%. it can.

Note that the time when the steering torque when the motor rotation speed is equivalent to the no-load rotation speed is stored in the memory 88 is arbitrary, and the motor rotation speed is constantly monitored while the vehicle is running. You may memorize | store when it becomes load rotation speed equivalent. In addition, the steering handle may be manually turned off at the time of vehicle pre-shipment inspection, periodic inspection, etc., and stored at that time.
The left / right difference adjustment unit 87 multiplies the steering wheel return assist torque output from the gain generation unit 84 by this correction coefficient and outputs the result.

In this way, the handle return control unit 73 can reliably generate torque in a direction in which the electric motor M returns the handle to the origin when the steering handle 51 is returned to the neutral position.
In this embodiment, when the driver is steering while holding the steering wheel, a steering assist torque signal for assisting steering is generated based on the steering torque signal, and the driver tries to return the steering wheel. In this case, a handle return assist torque signal that cancels the friction that prevents the handle from returning to the origin (neutral position) may be generated as an optimum value necessary to cancel the friction corresponding to the left and right rotation directions of the handle. it can.

Furthermore, in the present embodiment, the difference in the rotational direction of the steering wheel return force or the friction of the vehicle is learned, and the return force and the friction imbalance that differ depending on the return direction of the steering wheel are determined in the respective directions based on the learning result. By making it possible to adjust it to an appropriate value, an effect of automatically eliminating the left-right difference in the steering wheel return characteristic can be obtained.
Although the embodiments of the present invention have been described above, the embodiments of the present invention are not limited to the above-described embodiments. For example, the learning unit 86 as the “motor rotation direction determination means for determining the rotation direction of the electric motor” has determined the rotation direction of the electric motor M based on the terminal voltage of the electric motor M. You may determine based on a direction. Further, for a vehicle equipped with an electric motor having a small moment of inertia converted to a handle shaft, each gain of the inertial force compensator 82 may be set to zero. In this case, the motor rotation acceleration detector 66 and the inertial force compensator 82 It becomes unnecessary. In addition, various modifications can be made within the scope of the present invention.

53 ... Torque sensor, 61 ... Steering torque calculation unit, 71 ... Basic assist control unit, 55 ... Rotation angle sensor, 65 ... Motor rotation speed calculation unit 86 ... Learning unit, 87 ... Left / right difference adjustment unit for rotational torque, 88 ... Memory

Claims (3)

Steering torque detecting means for detecting steering torque generated by the driver rotating the steering wheel;
Basic assist control means for determining an assist torque for assisting the steering torque by the driver based on the steering torque detected by the steering torque detecting means;
Motor rotation speed detecting means for detecting the rotation speed of the electric motor for generating the assist torque;
Motor rotation direction determination means for determining the rotation direction of the electric motor;
Based on the motor rotation speed signal from the motor rotation speed detection means and the steering torque signal from the steering torque detection means, the steering torque when the motor rotation speed is equivalent to the no-load rotation speed is determined by the motor rotation direction determination means Storing means for storing each rotation direction of the electric motor determined by
With respect to the torque corresponding to the road surface reaction force of the tire that the tire receives from the road surface, the ratio of the steering torque in the rotational direction of each electric motor stored in the storage means with respect to the predetermined value of the rotational torque is used as a coefficient. A torque left / right difference adjusting means for adjusting,
An electric motor characterized in that steering wheel return control is performed by subtracting a torque corresponding to the road surface reaction force adjusted by the torque left-right difference adjusting means from the assist torque determined by the basic assist control means. Electric power steering device.   The electric motor-driven power steering apparatus according to claim 1, wherein the motor rotation direction determination unit determines a rotation direction of the electric motor based on a terminal voltage of the electric motor.   The electric electric motor according to claim 1, wherein a torque corresponding to a road surface reaction force of the tire is estimated based on an electric motor current flowing in the electric motor and a steering torque detected by the steering torque detecting means. Power steering device.

Images