JP2006282141A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device enabling a booster circuit to boost the battery voltage with good responsiveness and obtaining good steering feeling even in a situation in which a driver rapidly and largely turn a steering wheel. <P>SOLUTION: The electric power steering device comprises a steering torque sensor 4 to detect the steering torque applied on a steering shaft, a target current setting unit 19 to set the target current running in an electric motor 7 based on the detection signals from the steering torque sensor 4 and a vehicle speed sensor 5, a motor control unit 20 and a motor drive unit 21 to drive the electric motor 7 based on the target current signal from the target current setting unit 19, a battery 18 to supply the power to the electric motor 7 via the motor drive unit 21, and a booster circuit 22 to boost the battery voltage supplied from the battery 18 to the motor control unit 20. The booster circuit 22 is started according to the rate of change of the steering torque. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electric power steering apparatus that applies a driving force of an electric motor as a steering assist force to a steering system to reduce a steering force when a driver performs a steering operation.

  In recent years, as a power steering device for reducing the steering force of a steering wheel (steering handle), an electric power steering device that uses the power of an electric motor instead of the conventional hydraulic type is adopted in many vehicles. The electric power steering apparatus generally assists a driver's steering operation by boosting the rotational torque of an electric motor by a reduction mechanism and applying the torque to a rack shaft via a rack and pinion mechanism or the like.

  A conventional electric power steering device calculates a target current to flow to an electric motor based on a steering torque signal from a steering torque sensor provided on a steering shaft or the like, and based on an electric motor drive signal obtained based on the target current. An electric motor is driven to apply a steering assist force to the steering system. By the way, in the conventional electric power steering apparatus, the driver rotates the electric motor at high speed during a steering operation in which the driver rotates the steering wheel (steering handle) quickly and greatly (for example, at a corner having a small radius or parallel parking). Therefore, it is necessary to increase the steering assist force that acts on the steering system.

  However, when the driver rotates the steering wheel quickly and greatly (for example, at a corner having a small radius or parallel parking), the back electromotive force associated with the high-speed rotation of the electric motor increases. An increase in flowing current is suppressed, and the steering assist force may be insufficient. For this reason, when a large steering assist force as described above is required, it is necessary to increase the drive voltage applied to the electric motor. Therefore, an electric power steering device including a booster circuit that boosts the battery voltage of an in-vehicle battery (hereinafter referred to as a battery) that is a power source of the electric motor is known (see, for example, Patent Document 1).

The booster circuit of Patent Document 1 boosts the battery voltage based on the rotation speed of an electric motor that outputs a steering assist force and the value of a current (current command value) that flows through the electric motor.
JP 2003-54430 A (paragraph numbers [0016] and [0027], FIGS. 1 and 7)

  The booster circuit of Patent Document 1 uses the value of the current (current command value) that flows to the motor as described above for boosting control of the battery voltage. This current command value is determined based on assist torque calculated from information such as steering torque detected by the steering torque sensor, vehicle speed detected by the vehicle speed sensor, and rotation angle detected by the steering angle sensor.

  As described above, the current command value used for the boost control is determined based on the assist torque obtained from the sensor information detected by the steering torque sensor, the steering angle sensor, the vehicle speed sensor, and the like. There is a slight time lag (delay) between the detection of each sensor information by a sensor, a vehicle speed sensor and the like until the current command value is determined.

  Therefore, when the driver rotates the steering wheel quickly and greatly (for example, at a corner having a small radius or parallel parking), the booster circuit follows this even if the steering torque suddenly increases. The battery voltage cannot be boosted, and the battery voltage is boosted with a slight delay. For this reason, a delay occurs in the rotation start of the electric motor, and the steering feeling may deteriorate.

  Therefore, the present invention provides an electric motor that can obtain a good steering feeling by allowing the booster circuit to boost the battery voltage with good responsiveness even when the driver rotates the steering wheel quickly and greatly. An object is to provide a power steering apparatus.

  In order to achieve the above object, an electric power steering apparatus according to the first aspect of the present invention includes an electric motor, steering input detection means for detecting an input of a steering force to a steering system, and at least the steering input detection means. Target current setting means for setting a target current to flow to the electric motor based on the detection signal of the motor, motor drive control means for rotating the electric motor based on the target current signal from the target current setting means, and the motor Based on a detection signal from a battery for supplying electric power to the electric motor via a drive control means, a boosting means for boosting a battery voltage supplied from the battery to the motor drive control means, and a steering input detection means Boosting control means for activating the boosting means, and based on a signal from the steering input detecting means, the steering Of calculating the rate of change of the steering speed, and controls said boost control means in response to said change ratio.

  According to the first aspect of the present invention, the driver calculates the change rate of the steering speed of the steering system based on the signal from the steering input detection means, and controls the boost control means in accordance with the change rate. It is possible to quickly determine when the steering wheel is rotated quickly and greatly (for example, at a corner having a small radius or parallel parking), and the voltage booster can be activated with high responsiveness to boost the battery voltage.

  According to a second aspect of the present invention, the steering input detecting means is a steering torque detecting means for detecting a steering torque acting on the steering system, and the boost control means is a steering torque from the steering torque detecting means. The boosting means is activated based on a torque differential value calculated by differentiating the signal.

  According to the second aspect of the present invention, the booster is activated based on the torque differential value calculated by differentiating the steering torque signal from the steering torque detector, so that the driver can quickly and greatly increase the steering wheel. The battery voltage can be boosted by activating the boosting means with good responsiveness even when rotating (for example, at a corner having a small radius or parallel parking).

  According to a third aspect of the present invention, the steering input detecting means is a steering angle detecting means for detecting a steering angle corresponding to steering of a steering wheel, and the step-up control means is supplied from the steering angle detecting means. The step-up means is activated based on a steering angle differential value calculated by differentiating the steering angle signal.

  According to the third aspect of the present invention, the driver starts the steering wheel quickly by activating the boosting unit based on the steering angle differential value calculated by differentiating the steering angle signal from the steering angle detecting unit. The battery voltage can be boosted by activating the boosting means with good responsiveness even in the case of a large rotation (for example, at a corner having a small radius or parallel parking).

  The invention according to claim 4 is characterized in that the boosting means is stopped after a predetermined time has elapsed since the boosting control means started the boosting means.

  According to the fourth aspect of the invention, useless power consumption associated with the startup of the boosting means can be suppressed by stopping the boosting means after a predetermined time has elapsed after the startup.

  According to the electric power steering apparatus of the present invention, it is possible to quickly determine when the driver quickly and greatly rotates the steering wheel (for example, at a corner having a small radius or parallel parking), and boosting means with high responsiveness. Since the battery voltage can be boosted by starting up the electric motor, the electric motor can rise up and rotate with high responsiveness following a quick steering operation, and appropriate steering assist force can be generated with high responsiveness.

  Hereinafter, the present invention will be described based on the illustrated embodiments. FIG. 1 is a schematic configuration showing an electric power steering apparatus according to an embodiment of the present invention.

  As shown in FIG. 1, an electric power steering apparatus 1 according to this embodiment includes a steering shaft 3 coupled to a steering wheel 2, a steering torque sensor 4 that detects a steering torque that acts on the steering shaft 3, and a vehicle speed. A vehicle speed sensor 5 to detect, an electric motor (for example, a brushless DC motor) 7 that applies a steering assist force to the steering shaft 3 via the speed reduction mechanism 6, and a control device (ECU) 8 that controls the driving of the electric motor 7; , A motor current detector 9 for detecting a motor current flowing in the electric motor 7 and a rack shaft 11 connected via a rack and pinion mechanism 10. The tie rods 12 a, Steering wheels (front wheels) 13a and 13b are connected via 12b and the like. In the present embodiment, a steering system is constituted by the steering wheel 2, the steering shaft 3, and the rack shaft 11 connected via the rack and pinion mechanism 10.

  The speed reduction mechanism 6 has a function of boosting the rotational torque of the electric motor 7 and transmitting it to the steering shaft 3. For example, a worm gear (not shown) provided on the rotation shaft (output shaft) 14 of the electric motor 7. And a worm wheel (not shown) provided on the steering shaft 3. The rack and pinion mechanism 10 is configured by meshing a pinion 16 provided on a pinion shaft 15 connected to the steering shaft 3 and a rack 17 provided on the rack shaft 11. A battery (vehicle battery) 18 mounted on the vehicle is electrically connected to the control device 8 (details of the control device 8 will be described later).

  FIG. 2 is a schematic configuration diagram showing the control device 8 of the electric power steering device 1. As shown in FIG. 2, the control device 8 includes a target current setting unit 19, a motor control unit 20, a motor drive unit 21, a booster circuit (DC-DC converter) 22, and a booster circuit control unit 23.

The motor drive unit 21 includes an H-type bridge circuit composed of, for example, four power FETs (field effect transistors), and each power FET is based on a motor drive control signal V _D input from the motor control unit 20. each PWM (pulse width modulation) driving, by applying a predetermined drive voltage V _M to the electric motor 7 to drive the electric motor 7.

  The booster circuit 22 has a function of boosting the voltage from the battery 18 based on the start signal S from the booster circuit control unit 23 and supplying the boosted voltage to the motor drive unit 21. The drive voltage boosted from the unit 21 is applied to the electric motor 7.

Next, the operation of the electric power steering device 1 will be described.
When the driver steers the steering wheel 2, the rack shaft 11 is linearly reciprocated via the rack and pinion mechanism 10 by the steering torque applied to the steering shaft 3, and the steered wheels 13a, 13b, 13b is steered. At this time, the electric motor 7 is driven to apply an appropriate steering assist force to the steering shaft 3 so as to reduce the steering force when the driver steers the steering wheel 2.

  That is, the steering torque applied to the steering shaft 3 by the steering wheel 2 is detected by the steering torque sensor 4, and the steering torque signal T corresponding to the detected steering torque is output to the target current setting unit 19 of the control device 8. . Further, the vehicle speed is detected by the vehicle speed sensor 5, and a vehicle speed signal V corresponding to the detected vehicle speed is simultaneously output to the target current setting unit 19.

The target current setting unit 19 sets a target current value of a motor current to be supplied to the electric motor 7 based on the steering torque signal T input from the steering torque sensor 4 and the vehicle speed signal V input from the vehicle speed sensor 5. signal corresponding to the target current value (hereinafter, referred to as target current signal) I _T to the motor control unit 20.

The motor control unit 20, the arithmetic and the target current signal I _T input from the target current setting unit 19, a deviation between the motor current signal I _M corresponding to the motor current value of the electric motor 7 detected by the motor current detector 9 Then, P (proportional) / I (integral) control is performed on the obtained deviation signal to generate a motor drive control signal V _D for current feedback control.

The motor drive unit 21, the driving voltage V _M corresponding to the motor drive control signal V _D which is input is applied to the electric motor 7 to drive the electric motor 7. At this time, the booster circuit 22 may be activated by the control of the booster circuit control unit 23 to boost the battery voltage of the battery 18 and supply the boosted battery voltage to the motor drive unit 21 (boost by the booster circuit control unit 23). The activation control of the circuit 22 will be described later).

  Then, a predetermined steering assist force (assist force) is applied to the rack shaft 11 via the speed reduction mechanism 6 and the rack and pinion mechanism 10 by the rotational torque of the driven electric motor 7.

  By the way, when the electric power steering apparatus 1 operates, when the driver rotates the steering wheel 2 quickly and greatly (for example, at a corner having a small radius or parallel parking), the electric motor 7 rotates at high speed. Since the back electromotive force accompanying this increases, an increase in the current flowing through the electric motor 7 is suppressed, and the steering assist force may be insufficient. In such a case, the booster circuit 22 is activated under the control of the booster circuit control unit 23 to boost the battery voltage of the battery 18.

  Next, startup control of the booster circuit 22 will be described with reference to the flowcharts shown in FIGS.

  First, when the steering torque signal T detected by the steering torque sensor 4 is output to the target current setting unit 19 of the control device 8, it is also output to the booster circuit control unit 23 at the same time. The booster circuit control unit 23 differentiates the input steering torque signal T to obtain a torque differential value (change rate of the steering torque (that is, change rate of the steering speed of the steering wheel 2 during the driver's steering operation)). The noise is removed by applying the noise filter after the calculation (step S1).

  Then, it is determined whether or not the torque differential value obtained in step S1 is larger than a preset threshold value (step S2). If the torque differential value is smaller than this threshold value (step S2: No), Return to before step S1.

On the other hand, if it is determined in step S2 that the torque differential value is larger than this threshold value (step S2: Yes), the boost circuit control unit 23 outputs the start signal S to the boost circuit 22 to start the boost circuit 22. (Steps S3 and S4). When the booster circuit 22 is activated, and boosts the battery voltage supplied from the battery 18 to the motor driver 20, to quickly boosts the driving voltage V _M applied from the motor drive unit 21 to the electric motor 7. As a result, when the driver rotates the steering wheel 2 quickly and greatly (for example, at a corner having a small radius or parallel parking, etc.), the electric motor 7 rises and rotates with good responsiveness following a quick steering operation. In addition, an appropriate steering assist force can be generated with good responsiveness.

Then, the activation time after the booster circuit 22 is activated in step S4 is measured (step S5), and it is determined whether or not the measured activation time of the booster circuit 22 is longer than a predetermined time set in advance ( In step S6), when the measured startup time has passed this predetermined time (step S6: Yes), a startup stop signal is output from the booster circuit control unit 23 to the booster circuit 22 to stop the booster circuit 22 (step S7). , S8). When the step-up circuit 22 is stopped, with the battery voltage from the battery 18 is supplied to the motor driving section 21 applies a drive voltage V _M of the front boost to the electric motor 7 to drive the electric motor 7.

  If the startup time of the booster circuit 22 has not reached the predetermined time in step S6 (step S6: No), the process returns to step S6 and step S6 is continued until the startup time of the booster circuit 22 has passed the predetermined time. repeat.

  In this manner, the booster circuit control unit 23 differentiates the steering torque signal T input from the steering torque sensor 4 that directly detects the steering torque acting on the steering shaft 3 (steering wheel 2), and calculates a torque differential value ( Based on the change rate of the steering torque, the booster circuit 22 is activated to boost the battery voltage.

  Thereby, from the torque differential value (the rate of change of the steering torque) calculated from the steering torque signal T input from the steering torque sensor 4, for example, when the driver rotates the steering wheel 2 quickly and greatly (for example, It is possible to quickly determine a corner having a small radius (R), parallel parking, etc., and activate the booster circuit 22 with high responsiveness to boost the battery voltage. Therefore, even in a situation where the driver rotates the steering wheel 2 quickly and greatly (for example, at a corner having a small radius or parallel parking), the electric motor 7 rises with good responsiveness and rotates appropriately. By generating a sufficient steering assist force, it is possible to obtain a good steering feeling free from catching due to a pressure increase delay.

  Further, since the booster circuit 22 is stopped when a predetermined time elapses after the booster circuit 22 is started, it is possible to suppress wasteful power consumption accompanying the startup of the booster circuit 22.

  Further, in the startup control of the booster circuit 22 shown in the flowchart of FIG. 3, the booster circuit 22 is configured to stop after a predetermined time has elapsed from the startup as in steps S4 to S8. The booster circuit 22 may be stopped after the steering torque detected by the steering torque sensor 4 falls below a predetermined value after the circuit 22 is activated.

  In the present embodiment, the steering torque sensor 4 is used as a steering input detection means for detecting the steering force applied to the steering wheel 2 (steering shaft 3) by the driver's steering operation. A steering angle sensor that detects the steering angle of 2 (steering shaft 3) can also be used. In this case, the booster circuit control unit 23 activates the booster circuit 22 based on the steering angle differential value (steering angle change rate) calculated by differentiating the steering angle signal corresponding to the steering angle input from the steering angle sensor. Thus, the battery voltage can be boosted.

  Furthermore, a rack stroke sensor that detects the movement of the rack shaft 11 that linearly reciprocates as the driver steers the steering wheel 2 can be used as the steering input detection means.

  The present invention can also be applied to a structure (steer-by-wire) in which the steering wheel and the steered wheel of the steering system are mechanically separated and the electric motor generates all the steered force for the steered wheel. It is.

1 is a schematic configuration diagram showing an electric power steering device according to an embodiment of the present invention. The schematic block diagram which shows the control apparatus of the electric power steering apparatus which concerns on embodiment of this invention. The flowchart which shows the starting control of the booster circuit by a booster circuit control part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electric power steering apparatus 2 Steering wheel 3 Steering shaft 4 Steering torque sensor (steering input detection means)
5 Vehicle speed sensor 7 Electric motor 8 Control device 18 Battery 19 Target current setting unit (target current setting means)
20 Motor controller (motor drive control means)
21 Motor drive unit (motor drive control means)
22 Booster circuit (Boosting means)
23 Booster circuit controller (boost controller)

Claims (4)

An electric motor;
Steering input detection means for detecting the input of the steering force to the steering system;
Target current setting means for setting a target current to flow to the electric motor based on at least a detection signal from the steering input detection means;
Motor drive control means for rotationally driving the electric motor based on a target current signal from the target current setting means;
A battery for supplying electric power to the electric motor via the motor drive control means;
Boosting means for boosting the battery voltage supplied from the battery to the motor drive control means;
Boosting control means for activating the boosting means based on a detection signal from the steering input detection means,
Calculating a rate of change of the steering speed of the steering system based on a signal from the steering input detecting means, and controlling the boost control means according to the rate of change;
An electric power steering device. The steering input detection means is a steering torque detection means for detecting a steering torque acting on the steering system,
The boost control means activates the boost means based on a torque differential value calculated by differentiating a steering torque signal from the steering torque detection means;
The electric power steering apparatus according to claim 1. The steering input detection means is a steering angle detection means for detecting a steering angle according to steering of a steering wheel,
The boost control means starts the boost means based on a steering angle differential value calculated by differentiating a steering angle signal from the steering angle detection means.
The electric power steering apparatus according to claim 1. The boosting control means stops the boosting means after a predetermined time has elapsed since the boosting means was started;
The electric power steering apparatus according to any one of claims 1 to 3.

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