JP2012116240A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device for improving traveling stability and steering performance.SOLUTION: An EPS-ECU determines whether a steering wheel 2 is a steering increase state (that is, the forward side) in a Step S4, and sets steering increase time target steering torque Ttg as a target steering torque base value Ttb in a Step S5 when this determination is Yes. When a determination of the Step S4 is No, the EPS-ECU determines whether the steering wheel 2 is a steering return state (that is, the return side) in a Step S6, and sets steering return time target steering torque Ttr as the target steering torque base value Ttb in a Step S7 when this determination is Yes. When a determination of the Step S6 is also No (that is, when the steering wheel 2 is a nonrotating steering holding state), the EPS-ECU sets steering holding time target steering torque Tth as the target steering torque base value Ttb in a Step S8.

Description

  The present invention relates to an electric power steering apparatus mounted on a vehicle, and more particularly to a technique for improving running stability, steering performance, and the like.

  In recent automobiles, an electric power steering system (hereinafter referred to as EPS) that applies an assist torque by an electric motor is often used instead of the conventional hydraulic power steering apparatus. In the electric power steering device, there is no direct engine drive loss because an in-vehicle battery is used as the power source of the electric motor, and since the electric motor is started only at the steering assist, a decrease in driving fuel consumption can be suppressed, There is a feature that control by an ECU (electronic control unit) can be performed very easily.

  In the conventional EPS, since the assist torque of the electric motor is set according to the steering torque of the driver, it is difficult to consider factors such as the inertia of the electric motor and the friction of each part of the device, and the steering feeling is reduced. Was inevitable. Therefore, the target steering torque is obtained from the map based on the steering angle of the steering wheel, and the target assist torque is calculated based on the difference (steering torque difference) between the target steering torque and the detected value (actual steering torque) input from the steering torque sensor. A technique has been proposed in which feedback control is performed so as to match the target assist torque and the actual assist torque. According to this technique, the steering feeling described above is less likely to occur, and steering wheel turning (so-called steering wheel removal) caused by road surface irregularities (such as unevenness, undulation, rutting, etc.) during straight traveling or the like occurs. Even if it happens, stable running can be realized by generating an assist torque in a direction to correct the steering wheel (see Patent Document 1).

JP-A-6-56046

  However, in the method of Patent Document 1, since the steering angle of the steering wheel and the value of the target steering torque correspond uniquely, it may be difficult to perform smooth increase and return. For example, the driver may turn the steering wheel quickly when turning or avoiding obstacles, but the assist torque increases due to the instantaneous increase in the steering torque difference (that is, the steering reaction force decreases). ), Unstable vehicle behavior may occur due to excessive steering. On the other hand, the driver may loosen the hand attached to the steering wheel after finishing the turning, etc., but if the steering angle is large at this time, the target steering torque also increases, so the actual steering torque decreases ( Alternatively, a large steering torque difference occurs due to extinction). As a result, a large assist torque is generated in the direction of returning the steering wheel to the neutral position, and the steering wheel may return and rotate vigorously, causing the driver to feel uncomfortable or disturbing the vehicle behavior.

  The present invention has been made in view of such a background, and an object thereof is to provide an electric power steering device that realizes improvement in running stability, steering performance, and the like.

  In the first aspect of the present invention, an electric steering assist motor (9) for applying an assist force to the steering mechanism, a steering angle detecting means (11) for detecting a steering angle of the steering wheel (2), and the steering Target steering torque setting means (46, 47) for setting the target steering torque of the steering wheel based on the detection result of the angle detection means, and actual steering torque detection means for detecting the actual steering torque applied to the steering wheel from the driver (12), a steering torque difference calculation means (48) for calculating a difference between the target steering torque and the actual steering torque as a steering torque difference, and a target drive current is set based on the calculation result of the steering torque difference calculation means Target drive current setting means (36) for performing, and motor drive control means (22) for driving and controlling the steering assist motor with the target drive current; The target steering torque setting means (46, 47) sets the target steering torque when the steering wheel is increased as the first target steering torque (42), so that the steering wheel is turned off. The target steering torque at the time of return is set as the second target steering torque (44).

  In the second aspect of the present invention, the target steering torque setting means sets the first target steering torque to be larger than the second target steering torque.

  According to the present invention, for example, even when the driver turns the steering wheel quickly during turning or avoiding obstacles, the first target steering torque is relatively large, so that the steering torque difference is reduced and appropriate steering is performed. It becomes possible to operate the steering wheel with a reaction force. On the other hand, even if the driver loosens his hand attached to the steering wheel after turning, etc., the steering torque difference is reduced because the second target steering torque is relatively small, and the steering wheel suddenly returns due to the assist torque. Rotation is less likely to occur.

It is a schematic structure figure of an electric power steering device concerning an embodiment concerning an embodiment. It is a block diagram which shows schematic structure of EPS-ECU which concerns on embodiment. It is a block diagram which shows schematic structure of the steering torque difference calculation part which concerns on embodiment. It is a base value map at the time of increase which concerns on embodiment. It is a steering hold base value map which concerns on embodiment. It is a base value map at the time of switch back concerning an embodiment. It is a vehicle speed gain map at the time of increasing according to the embodiment. It is a vehicle speed gain map at the time of steering according to the embodiment. It is a vehicle speed gain map at the time of switching which concerns on embodiment. It is a flowchart which shows the procedure of the steering torque difference setting process which concerns on embodiment. It is a graph which shows the target steering torque which concerns on embodiment.

  Hereinafter, an embodiment in which the present invention is applied to an electric power steering apparatus for a passenger car will be described in detail with reference to the drawings.

<< Configuration of Embodiment >>
<Electric power steering device>
As shown in FIG. 1, the electric power steering apparatus 1 includes a pinion 4 connected to a steering wheel 2 via a steering shaft 3 and a rack 5 that meshes with the pinion 4 and reciprocates in the vehicle width direction. Equipped with an and pinion mechanism. Both ends of the rack 5 are connected to the knuckle arms 8 on the left and right front wheels 7 via the tie rods 6, and the left and right front wheels 7 are steered according to the rotation operation of the steering wheel 2. A steering assist mechanism 9 including a motor, a gear, and the like is coaxially mounted on the rack 5, and the driver's steering force is reduced by the assist torque generated by the steering assist mechanism 9.

  The steering shaft 3 is provided with a steering angle sensor 11 for detecting the steering angle of the steering wheel 2, and a steering torque sensor 12 for detecting steering torque is provided in the vicinity of the pinion 4. A vehicle speed sensor 13 for detecting the vehicle speed and a yaw rate sensor 14 for detecting the actual yaw rate of the vehicle body are provided at appropriate positions of the vehicle body. The steering assist mechanism 9 is provided with a resolver 15 that detects a motor rotation angle.

  Output signals of these sensors 11 to 15 are input to a steering control device (EPS-ECU) 21. The EPS-ECU 21 controls the electric power steering apparatus 1 in an integrated manner, and includes a microcomputer, ROM, RAM, peripheral circuits, input / output interfaces, various drivers, and the like, and performs target control based on the output signals described above. The amount (target current) is determined and output to the drive circuit 22 of the steering assist mechanism 9. The drive circuit 22 is configured by an FET bridge or the like, and supplies power to the steering assist mechanism 9 based on the target control amount determined by the EPS-ECU 21, thereby assist torque applied from the steering assist mechanism 9 to the rack 5. Is controlled.

<EPS-ECU>
As shown in FIG. 2, the EPS-ECU 21 includes a return determination unit 31, an angular velocity calculation unit 32, an assist torque setting unit 33, a damper compensation unit 34, a steering reaction force setting unit 35, and a target current setting. The part 36 is furnished.

  Based on the output signals of the steering angle sensor 11 and the steering torque sensor 12, the return determination unit 31 determines whether the steering direction is going (direction in which the steering direction is away from the neutral position) or returning (direction in which the steering direction is returned to the neutral position). The determination result is output to the assist torque setting unit 33. The angular velocity calculation unit 32 calculates the angular velocity of the steering assist mechanism 9 based on the output signal of the resolver 15 and outputs the angular velocity signal to the damper compensation unit 34. The damper compensation unit 34 sets the attenuation correction value of the steering assist mechanism 9 based on the output signals of the steering angle sensor 11, the yaw rate sensor 14, and the angular velocity calculation unit 32, and outputs this to the assist torque setting unit 33.

  The assist torque setting unit 33 includes a steering torque difference calculation unit 40 and the like which will be described later, and includes a steering torque difference Dts calculated by the steering torque difference calculation unit 40, a vehicle speed sensor 13, a yaw rate sensor 14, a damper compensation unit 34, and the like. The assist torque target value Tat is set based on the input signal and is output to the target current setting unit 36.

  The steering reaction force setting unit 35 sets the steering reaction force target value force Trt based on the output signals of the angular velocity calculation unit 32 in addition to the output signals of the steering angle sensor 11, the steering torque sensor 12, the vehicle speed sensor 13, and the yaw rate sensor 14. This is output to the target current setting unit 36.

  The target current setting unit 36 sets a target current It based on the assist torque target value Tat input from the assist torque setting unit 33 and the steering reaction force target value force Trt input from the steering reaction force setting unit 35. Output to the drive circuit 22.

<Steering torque difference calculation unit>
As shown in FIG. 3, the steering torque difference calculation unit 40 includes a steering region determination unit 41, a turning-up base value setting unit 42, a steering holding base value setting unit 43, and a switching-back base value setting unit 44. A steering angular velocity calculation unit 45, a target steering torque selection unit 46, a multiplier 47, an adder 48, an increasing vehicle speed gain setting unit 51, a steered vehicle speed gain setting unit 52, and a return time The vehicle speed gain setting unit 53 and vehicle speed gain multipliers 54 to 56 are configured.

  The steering region determination unit 41 determines the steering region (whether the steering wheel 2 is on the left or right side from the neutral position) based on the output signal of the steering torque sensor 12. The increase base value setting unit 42 sets a relatively large increase base value Ttgb with respect to the steering angle θ as shown in the increase base value map of FIG. The holding time base value setting unit 43 sets a holding time base value Tthb having a medium magnitude with respect to the steering angle θ, as shown in the holding time base value map of FIG. The return-time base value setting unit 44 sets a relatively smaller return-time base value Ttrb with respect to the steering angle θ as shown in the return-time base value map of FIG.

  The steering angular velocity calculation unit 45 calculates the steering angular velocity ω by differentiating the steering angle θ with respect to time. The target steering torque selection unit 46 has three target steering torques Ttg and Tth based on the calculation result of the steering angular velocity calculation unit 45 (whether the steering state or the steering holding state) and the determination result of the return determination unit 31. , Ttr is selected as the target steering torque base value Ttb. The multiplier 47 determines the sign of the target steering torque base value Ttb based on the determination result of the steering region determination unit 41, and outputs the target steering torque Ttgt. The adder 48 subtracts the actual steering torque Treal from the target steering torque Ttgt, and outputs a steering torque difference Dts.

  The increasing vehicle speed gain setting unit 51 sets a relatively large increasing vehicle speed gain Gvg with respect to the vehicle speed V as shown in the increasing vehicle speed gain map of FIG. The holding time base value setting unit 43 sets a holding time eye vehicle speed gain Gvh having a medium magnitude with respect to the vehicle speed V, as shown in the holding time vehicle speed gain map of FIG. The switchback base value setting unit 44 sets a relatively small switchback vehicle speed gain Gvr with respect to the vehicle speed V as shown in the switchback vehicle speed gain map of FIG.

<< Operation of Embodiment >>
When the automobile starts traveling, the EPS-ECU 21 repeatedly executes steering assist control at a predetermined processing interval (for example, 10 ms). When the steering assist control is started, the EPS-ECU 21 sets the assist torque target value Tat by performing damper compensation or the like on a steering torque difference Dts (to be described later) by the assist torque setting unit 33, while steering by the steering reaction force setting unit 35. Reaction force torque Trt is set. Next, the EPS-ECU 21 sets the target current It based on the assist torque target value Tat and the steering reaction force torque Trt in the target current setting unit 36 and outputs the target current It to the drive circuit 22. As a result, an assist force is applied from the steering assist mechanism 9 to the rack 5 to reduce the driver's steering burden.

<Setting of steering torque difference>
The EPS-ECU 21 executes a steering torque difference setting process whose procedure is shown in the flowchart of FIG. 10 in parallel with the steering assist control described above.
When the steering torque difference setting process is started, the EPS-ECU 21 calculates the target steering torque at the time of increase from the base value Ttgb at the time of increase and the vehicle speed gain Gvg at the time of increase based on the current steering angle θ and the vehicle speed V. Ttg is set, and in step S2, the steering-time target steering torque Tth is set from the holding-time base value Tthb and the steering-time eye speed gain Gvh. In step S3, the return-time base value Ttrb and the return-time vehicle speed gain are set. The target steering torque Ttr at the time of return is set from Gvr.

  Next, the EPS-ECU 21 determines in step S4 whether or not the steering wheel 2 is in an increased state (that is, on the going side). If this determination is Yes, in step S5, the target steering torque Ttg at the time of increase is increased. Is the target steering torque base value Ttb.

  If the determination in step S4 is No, the EPS-ECU 21 determines in step S6 whether or not the steering wheel 2 is in the switchback state (that is, the return side), and if this determination is Yes. In step S7, the target steering torque Ttr at the time of return is set as a target steering torque base value Ttb.

  If the determination in step S6 is also No (that is, if the steering wheel 2 is in a steered state where it is not rotating), the EPS-ECU 21 sets the steered target steering torque Tth as the target steering in step S8. The torque base value is Ttb.

  Next, the EPS-ECU 21 determines in step S9 whether or not the position of the steering wheel 2 is to the right of the neutral position. If this determination is Yes, the target steering torque base value Ttb is directly used in step S10. The target steering torque Ttgt is set. If No, the target steering torque base value Ttb having a negative sign is set as the target steering torque Ttgt in step S11.

  Next, the EPS-ECU 21 calculates / outputs the steering torque difference Dts by subtracting the actual steering torque Treal from the target steering torque Ttgt in step S12.

  As shown in FIG. 11, the target steering torque Ttgt has an absolute value that increases when the target steering torque Ttgt is increased with respect to the time when the steering is maintained, and decreases when the target steering torque Ttgt is switched back with respect to the time that the steering is maintained. As a result, the steering stability is improved by generating a certain steering reaction force when the turning is increased, while sudden return rotation of the steering wheel 2 due to an excessive steering reaction force is less likely to occur at the time of turning back. It should be noted that the steering torque difference Dts (i.e., assist torque in a direction to correct the steering wheel removal) even when steering wheel is pulled due to road surface irregularities, such as when steering is held, when steering is increased, or when switching back. ) Can be achieved to achieve stable running.

  This is the end of the description of specific embodiments. However, aspects of the present invention are not limited to these embodiments. For example, in the above-described embodiment, the present invention is applied to EPS using a brushless motor as an assist motor of the steering assist mechanism, and the angular velocity detection unit detects the angular velocity of the assist motor based on the output signal of the resolver. The invention is naturally applicable to EPS using a brush motor as an assist motor. In that case, the angular velocity of the assist motor may be detected by time-differentiating the detected value of the steering angle sensor. In the above embodiment, the target steering torque at the time of steering is set based on the dedicated map at the time of steering (the base value map at the time of steering and the vehicle speed gain map at the time of steering). You may make it set the target steering torque at the time of a steering hold based on a map (map for the time of an increase or a map at the time of a return). In the above embodiment, as the vehicle speed gain map, the gains for the vehicle speed are different from each other at the time of increasing, at the time of holding, and at the time of returning, but these may be the same. Furthermore, specific configurations of the electric power steering device and EPS-ECU, specific control procedures, and the like can be appropriately changed without departing from the gist of the present invention.

DESCRIPTION OF SYMBOLS 1 Electric power steering apparatus 2 Steering wheel 5 Rack 7 Left and right front wheel 9 Steering assist mechanism (steering assist motor)
11 Steering angle sensor (steering angle detection means)
12 Steering torque sensor (actual steering torque detection means)
21 Steering control device 21 EPS-ECU
33 Assist torque setting unit 40 Steering torque difference calculation unit (steering torque difference calculation means)
41 Steering region determination unit 42 Base value setting unit at the time of increase (target steering torque setting unit)
43 Steering time base value setting unit (target steering torque setting unit)
44 Base value setting unit at the time of return (target steering torque setting unit)
46 Target steering torque selector

Claims (2)

An electric steering assist motor for applying assist force to the steering mechanism;
Steering angle detection means for detecting the steering angle of the steering wheel;
Target steering torque setting means for setting a target steering torque of the steering wheel based on the detection result of the steering angle detection means;
An actual steering torque detecting means for detecting an actual steering torque applied to the steering wheel from the driver;
A steering torque difference calculating means for calculating a difference between the target steering torque and the actual steering torque as a steering torque difference;
Target drive current setting means for setting a target drive current based on the calculation result of the steering torque difference calculation means;
An electric power steering device comprising motor drive control means for driving and controlling the steering assist motor with the target drive current;
The target steering torque setting means sets the target steering torque when the steering wheel is increased as the first target steering torque, and sets the target steering torque when the steering wheel is switched back as the second target steering torque. Electric power steering device.   The electric power steering apparatus according to claim 1, wherein the target steering torque setting means sets the first target steering torque to be larger than the second target steering torque.

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