JP2006131064A - Steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve control accuracy by controlling steering at good response. <P>SOLUTION: A detection unit 18 directly detects a lateral force Fy acting on wheels 5 while front wheels 5 and rear wheels 5 are detection objects. An actuator 11 is installed to a steering system for transmitting an operation volume of a handle 6 operated by a driver to the wheels, and adds an assist torque to the steering system. A processing unit 12a corrects the assist torque added to the steering system based on a lateral force Ff_y acting on the front wheels 5 and a lateral force Fr_y acting on the rear wheels 5. A control unit 12b controls the actuator 11 based on the corrected assist torque. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a steering device.

Conventionally, a power steering device that assists a driver's steering wheel operation and a steering device that employs a steer-by-wire mechanism in which a steering system from a steering wheel to a steering wheel is mechanically separated are known. For example, Patent Literature 1 discloses a power steering device that adjusts an assist amount in accordance with a yaw rate generated in a vehicle. The same patent document also discloses a steering device of a steer-by-wire mechanism that adjusts an assist amount (steering reaction force amount) according to a yaw rate generated in a vehicle.
JP 2003-252229 A

  When a steering operation is performed by a driver, a slip angle is generated on the steered wheel (usually the front wheel), thereby generating a lateral force on the steered wheel. When a moment is applied to the vehicle due to the lateral force and the direction of the vehicle is changed, a slip angle is generated on the non-steering wheel (usually the rear wheel), thereby generating a lateral force on the non-steering wheel. In such a series of turning processes, a change in the behavior of the vehicle accompanying the turning appears with a timing delay from the driver's steering operation. Therefore, the conventional sensing method for detecting the yaw rate from the behavior of the vehicle has the disadvantage that the control responsiveness is poor.

  Therefore, an object of the present invention is to improve control accuracy by performing steering control with high responsiveness.

  In order to solve this problem, the present invention provides a steering device. This steering device uses a front wheel and a rear wheel as detection targets, a detection unit that directly detects lateral force acting on the wheel, and a steering system that transmits an operation amount of a handle operated by a driver to the wheel. An actuator that applies assist torque to the steering system, a processing unit that corrects assist torque applied to the steering system based on the lateral force acting on the front wheels and the lateral force acting on the rear wheels, and the corrected And a control unit that controls the actuator based on the assist torque.

  Here, the present invention further includes a torque sensor that detects a steering torque applied to the steering system by a driver's steering operation, and a vehicle speed sensor that detects a vehicle speed, and the processing unit is identified as the detected vehicle speed. It is preferable to set an initial value of the assist torque as a correction target based on the steering torque.

  In the present invention, the processing unit estimates the change in the yaw rate generated in the vehicle by comparing the lateral force acting on the front wheel and the lateral force acting on the rear wheel, and the estimated yaw rate change. Accordingly, it is preferable to correct the initial value of the assist torque.

  Further, in the present invention, when the processing unit determines that the steer characteristic is oversteer based on the estimated change in the yaw rate, the processing unit corrects the initial value so that the assist torque becomes smaller than the initial value, and estimates When the steering characteristic is determined to be understeer based on the change in the yaw rate, it is preferable to correct the initial value so that the assist torque is larger than the initial value.

  According to the present invention, the assist torque is applied to the steering system by the actuator provided in the steering system, and the assist torque is corrected based on the lateral force acting on the front wheels and the rear wheels. Since the lateral force acting on the wheels is directly detected, steering control can be performed with high responsiveness. Further, since the lateral force can be specified with high accuracy by direct detection, the control accuracy can be improved. In addition, according to the present invention, by correcting the assist torque so as to suppress the change in the yaw rate during cornering, it is possible to prompt the driver to perform quick correction steering, and to improve the maneuverability.

(First embodiment)
FIG. 1 is an explanatory diagram of a vehicle to which the steering device according to the first embodiment is applied. This vehicle is a four-wheel drive vehicle driven by four front and rear wheels. Power from a crankshaft (not shown) of the engine 1 is transmitted to a front wheel side and a rear wheel side drive shaft (axle) 4 via an automatic transmission 2 and a center differential device 3, respectively. When power is transmitted to the axle 4, rotational torque is applied to the wheel 5, and thereby driving force is applied to the wheel 5.

  When the steering wheel 6 is operated by the driver, the steering angle of the front wheel 5 that is a steering wheel is controlled by the steering device 10. The steering device 10 of the present embodiment is an electric power steering device that assists the driver's steering with the power from the actuator. The steering device 10 is mainly composed of a steering system that transmits an operation amount of the handle 6 to the front wheels 5, an electric motor 11 as an actuator, and a control unit 12.

  The steering system mechanically connects between the handle 6 and the wheel 5, and mainly includes a steering shaft 13, a pinion shaft 14, a rack 15, and a tie rod 16. A handle 6 is attached to the upper end of the steering shaft 13, and a pinion shaft 14 is attached to the lower end thereof. A rack 15 provided in the vehicle width direction meshes with the lower end of the pinion shaft 14, that is, the pinion. By this rack and pinion mechanism, the rotational movement of the steering shaft 13 is converted into the straight movement (translational movement) of the rack 15. A knuckle arm (not shown) provided on the front wheel 5 is connected to both ends of the rack 15 via a tie rod 16, and the left and right front wheels 5 are steered by moving the rack 15 in the horizontal direction (translational movement). An angle is given.

  A ring gear 17 constituting a speed reducer is mounted on the shaft above the pinion shaft 14, and the drive shaft of the electric motor 11 is connected to the ring gear 17. Power from the electric motor 11 is applied to the pinion shaft 14 via the ring gear 17. Therefore, in addition to the steering torque from the driver, the assist torque from the electric motor 11 is applied to the steering system.

  FIG. 2 is a block configuration diagram of the steering device 10 including the control unit 12. As the control unit 12, a microcomputer mainly composed of a CPU, a ROM, a RAM, and an input / output interface can be used. The control unit 12 controls the output of the electric motor 11 and controls the assist torque. In order to control the output of the electric motor 11, detection signals are input to the control unit 12 from various sensors including the detection unit 18.

  FIG. 3 is an explanatory diagram of the acting force acting on the wheel 5. The detection unit 18 detects the acting force acting on the wheel 5. For convenience of explanation, FIG. 2 shows only one block corresponding to the detection unit 18, but actually the detection unit 18 is provided corresponding to each wheel 5. The acting force that can be detected by the detection unit 18 includes a longitudinal force Fx, a lateral force Fy, and a vertical force Fz. The longitudinal force Fx is a component force generated in the direction parallel to the wheel center plane (x-axis) of the friction force generated on the ground contact surface of the wheel 5, and the lateral force Fy is a direction perpendicular to the wheel center plane (y This is the component force generated on the shaft. On the other hand, the vertical force Fz is a force acting in the vertical direction (z-axis), that is, a so-called vertical load. In the present embodiment, the lateral force Fy is important among these acting forces. Each detection unit 18 is mainly configured by a strain gauge and a signal processing circuit that processes an electrical signal output from the strain gauge and generates a detection signal corresponding to the acting force. Based on the knowledge that the stress generated on the axle 4 is proportional to the acting force, the acting force is directly detected by embedding a strain gauge in the axle 4. The specific configuration of the detection unit 18 is disclosed in, for example, Japanese Patent Application Laid-Open Nos. 04-331336 and 10-318862, and should be referred to if necessary.

  The torque sensor 19 detects a steering torque Ts applied to the steering system by a driver's steering operation. A torsion bar 20 that is twisted in accordance with the rotational force applied to the handle 6 is provided at an intermediate portion of the steering shaft 13. The torque sensor 19 detects the steering torque Ts from the twist amount and twist direction of the torsion bar 20. The vehicle speed sensor 21 (not shown in FIG. 1) is a sensor that detects the vehicle speed, so-called vehicle speed v, based on the rotational speed of the wheels 5.

  When the microcomputer that is the control unit 12 is functionally grasped, the control unit 12 includes a processing unit 12a and a control unit 12b. The processing unit 12a sets an initial value Tai of assist torque to be applied to the steering system based on the steering torque Ts and the vehicle speed v. Further, the processing unit 12a corrects the set initial value Tai based on the lateral force Fy acting on the wheel 5. The control unit 12b performs output control of the electric motor 11 so that the assist torque (correction value Taa) corrected by the processing unit 12a is applied to the steering system.

  FIG. 4 is a flowchart showing a control routine of the steering device 10 according to the present embodiment. This routine is called at predetermined intervals and executed by the control unit 12. In this specification, for convenience, the yaw rate acting in the turning direction is treated as positive, and the lateral force Fy acting in the turning direction is treated as positive. That is, when turning left, the counterclockwise (counterclockwise) yaw rate is positive, and the lateral force Fy acting in the left direction is positive. On the other hand, when turning right, contrary to left turning, the clockwise (rightward) yaw rate is positive, and the lateral force Fy acting in the right direction is positive. As for the assist torque, the torque that applies force in the steering direction of the driver is treated as positive.

  First, in step 1, various detection values are read. The detection values read in Step 1 include the lateral force Fy acting on each wheel 5, the steering torque Ts, and the vehicle speed v. In step 2, a front wheel lateral force Ff_y and a rear wheel lateral force Fr_y are calculated. The front wheel lateral force Ff_y is a value indicating the lateral force Fy acting on the front wheel 5, and is calculated based on the lateral force Fy of the left and right front wheels 5. On the other hand, the rear wheel lateral force Fr_y is a value indicating the lateral force Fy acting on the rear wheel 5, and is calculated based on the lateral force Fy of the left and right rear wheels 5. As these lateral forces Ff_y and Fr_y, the average value of the lateral forces Fy of the left and right wheels 5, the sum of the lateral forces Fy of the left and right wheels 5, or the lateral force Fy of one of the left and right wheels 5 is used. Can be used as a value.

  In step 3 following step 2, an initial value Tai of assist torque is set. The initial value Tai is determined in consideration of the steering torque Ts and the vehicle speed v from the viewpoint of improving the steering feel. First, the initial value Tai has a proportional relationship with the steering torque Ts. That is, the initial value Tai increases as the steering torque Ts increases, and decreases as the steering torque Ts decreases. Second, the initial value Tai has an inversely proportional relationship with the vehicle speed v. That is, the initial value Tai decreases as the vehicle speed v increases, and the value Tai increases as the vehicle speed v decreases. In such a vehicle speed sensitive setting method, the steering wheel 6 tends to be heavy when driving at a high speed, and the steering stability can be improved, and the steering wheel 6 tends to become light when driving at a low speed. Improvements can be made. The correspondence relationship between the assist torque (initial value) Tai, the vehicle speed v, and the steering torque Ts is created in advance as a map through experiments and simulations, and is stored at a predetermined address in the ROM of the control unit 12.

  In step 4, the change in the yaw rate generated in the vehicle, that is, the yaw angular acceleration γ ′ is estimated. In the case where the steering characteristic of the vehicle is oversteer or understeer, an unbalance occurs between the front wheel lateral force Ff_y and the rear wheel lateral force Fr_y, and therefore, yaw angular acceleration γ ′ occurs (γ ′ ≠ 0). ). Therefore, in step 4, the yaw angular acceleration γ ′ is estimated based on the value obtained by subtracting the rear wheel lateral force Fr_y from the front wheel lateral force Ff_y. The yaw angular acceleration γ ′ increases as the degree of unbalance between the front wheel lateral force Ff_y and the rear wheel lateral force Fr_y increases (the absolute value), and the unbalance between the front wheel lateral force Ff_y and the rear wheel lateral force Fr_y. The smaller the degree of balance, the smaller the value (absolute value).

  In step 5, it is determined whether or not the yaw angular acceleration γ ′ is “0”. If a negative determination is made in step 5, that is, if the yaw angular acceleration γ ′ is not “0”, the process proceeds to step 6. On the other hand, if an affirmative determination is made in step 5, that is, if the yaw angular acceleration γ ′ is “0”, step 6 is skipped and the process proceeds to step 7 described later.

  In step 6, correction processing is performed. In this correction process, the set assist torque initial value Tai is corrected based on the estimated yaw angular acceleration γ ′. Specifically, when the yaw angular acceleration γ ′ is positive (front wheel lateral force Ff_y> rear wheel lateral force Fr_y), that is, when it is determined that the steer characteristic is oversteer, a predetermined correction amount ΔT from the initial value Tai. Is calculated as the assist torque correction value Taa (Taa = Tai−ΔT). On the other hand, when the yaw angular acceleration γ ′ is negative (front wheel lateral force Ff_y <rear wheel lateral force Fr_y), that is, when the steering characteristic is determined to be understeer, a value obtained by adding a predetermined correction amount ΔT from the initial value Tai. Is calculated as the assist torque correction value Taa (Ta = Tai + ΔT). The correction amount ΔT is determined according to the magnitude of the absolute value of the yaw angular acceleration γ ′, and has a proportional relationship with, for example, the yaw angular acceleration γ ′ (absolute value). That is, the value ΔT of the correction amount ΔT increases as the yaw angular acceleration γ ′ increases, and the value ΔT decreases as the yaw angular acceleration γ ′ decreases. The relationship between the correction amount ΔT and the yaw angular acceleration γ ′ (absolute value) is created in advance as a map through experiments and simulations, and is stored at a predetermined address in the ROM of the control unit 12. Therefore, in step 6, the correction amount ΔT is uniquely set with reference to the map. It is not always necessary to use a map, and the correction amount ΔT may be calculated by multiplying the yaw angular acceleration γ ′ by a predetermined coefficient.

  In step 7, the output control of the electric motor 11 is performed based on the assist torque correction value Taa. Specifically, the target current signal is determined by multiplying the correction value Taa by the control gain. Then, a voltage to be applied to the electric motor 11 is determined based on the target current signal, and this voltage is applied to the electric motor 11. When the current value of the electric motor 11 changes according to the applied voltage, assist torque (correction value Taa) is applied to the steering system by the power of the electric motor 11. If the process of step 6 is skipped, the initial value Tai of the assist torque is not corrected. In this case, however, the correction amount ΔT is considered to be “0”, and this initial value Tai itself is used as the correction value Taa. Think.

  As described above, according to the present embodiment, the yaw rate change (yaw angular acceleration γ ′) is estimated from the imbalance between the front wheel lateral force Ff_y and the rear wheel lateral force Fr_y, and the assist torque is corrected according to the yaw rate change. Is done. In this correction, when the vehicle has an oversteer tendency, the assist torque is corrected to be smaller than the initial value Tai. Accordingly, the driver is given a feeling that the handle 6 becomes heavy, and therefore, an effect of assisting steering in a direction in which the handle 6 is returned is achieved. On the other hand, when the vehicle has an understeer tendency, the assist torque is corrected to be larger than the initial value Tai. Accordingly, the driver is given a feeling that the handle 6 becomes lighter, so that an effect of assisting steering in the direction of turning the handle 6 is exhibited. Thereby, the effect of assisting the operation of the driver is exhibited so that the change in the yaw rate during cornering is suppressed.

  The change in the yaw rate having a correlation with the vehicle steer characteristic can also be detected by a sensor or the like. However, the detection of the yaw rate by the sensor has a disadvantage in that the response is poor because a change in the direction of the vehicle body that occurs as a result of the lateral force Fy acting is detected. On the other hand, since the change in the lateral force Fy appears earlier than the change in the direction of the vehicle body, the control can be realized with high responsiveness by specifying the change in the yaw rate from the lateral force Fy. In this embodiment, since the lateral force Fy acting on the wheel 5 is directly detected, this value can be specified with high accuracy. Thereby, the control accuracy can be improved.

  Further, in the conventional power steering control, there is a method of correcting the assist torque when the lateral acceleration of the vehicle exceeds a limit value, that is, correcting the assist torque with respect to steering (for example, Japanese Patent Laid-Open No. 10-101). 315998). On the other hand, in the present embodiment, the control is performed based on the lateral force Fy, so that the assist torque is corrected even when the lateral force changes due to disturbance or the like during turning. As a result, it is possible to cope with a yaw rate change caused by other than steering, so that the control accuracy can be improved.

  Further, in the conventional power steering control, there is a method of performing control according to the lateral grip force of the rear wheel (for example, Japanese Patent Laid-Open No. 11-48997). On the other hand, in the present embodiment, the assist torque is corrected according to the yaw angular acceleration γ ′ due to the balance change between the front wheel lateral force Ff_y and the rear wheel lateral force Fr_y. Therefore, it is possible to apply assist torque that prompts the driver to make corrections, such as lighter for understeer and heavier for oversteer. Therefore, this embodiment is different from the present embodiment in which control is performed from the viewpoint of imbalance of the lateral force Fy.

(Second Embodiment)
FIG. 5 is an explanatory diagram of a vehicle to which the steering device according to the second embodiment is applied. The present embodiment is different from the first embodiment in that a steer-by-wire mechanism in which a steering system that connects a steering wheel (front wheel) 5 and a handle 6 to the steering device 10 is mechanically separated is employed. Is a point. Note that in the second embodiment, the same components as those described in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  A first power transmission mechanism 22 is connected to the other end of the steering shaft 13 to which the handle 6 is attached at one end, and a first electric motor 23 as an actuator is connected to the first power transmission mechanism 22. The output shaft is connected. The power generated in the first electric motor 23 is transmitted to the handle 6 as a negative assist torque, that is, a steering reaction force, via the first power transmission mechanism 22 and the steering shaft 13. On the other hand, the steering angle of the front wheel 5 is set by the second electric motor 24. The output shaft of the second electric motor 24 is connected to the second power transmission mechanism 25, and the power in the second electric motor 24 is transmitted to the pinion shaft 14 via the second power transmission mechanism 25. Is transmitted to. When the pinion shaft 14 is rotated by the power generated in the second electric motor 24, the rack 15 is displaced in the axial direction, and the steering angle of the front wheels 5 is changed according to the displacement.

  The first and second electric motors 23 and 24 are controlled by the control unit 12. In order to control the output of these electric motors 23 and 24, the control unit 12 receives detection signals from the sensors 26 to 28 in place of the torque sensor 19 in the first embodiment. The handle angle sensor 26 is attached to the steering shaft 13 and detects the handle angle of the handle 6 (for example, the rotation angle from the neutral position). The steering angle sensor 27 is attached to the pinion shaft 14 and detects the steering angle of the front wheel 5 by detecting the rotation angle of the pinion shaft 14 (rotation angle from the neutral position). The road surface reaction force sensor 28 is attached to the pinion shaft 14 and detects torque (road surface reaction force torque) acting on the pinion shaft 14.

  When controlling the steering angle of the front wheels 5, the control unit 12 first identifies the steering gear ratio based on the vehicle speed v. Normally, the steering gear ratio is variably set according to the vehicle speed v, and is uniquely determined by referring to a map or the like in which the correspondence relationship between the steering gear ratio and the vehicle speed v is appropriately set through experiments and simulations. Identified. Next, a target steering angle, which is a target value of the steering angle, is calculated based on the identified steering gear ratio and the detected steering wheel angle. Then, a control amount of the second electric motor 24 for realizing the target steering angle is calculated based on the detected current steering angle. Based on the calculated control amount, output control of the second electric motor 24 is performed, and the steering angle of the wheel 5 is adjusted to the target steering angle.

  Further, the control unit 12 determines a torque coefficient corresponding to the vehicle speed v with reference to a coefficient table created in advance through experiments and simulations. Based on the determined torque coefficient, the detected steering wheel angle, and the detected road surface reaction force torque, an initial value Tai of the assist torque is calculated. Then, according to the control routine shown in FIG. 4, the initial value Tai of the assist torque is corrected based on the front wheel lateral force Ff_y and the rear wheel lateral force. Specifically, when it is determined that the steer characteristic is oversteer, a value obtained by subtracting a predetermined correction amount ΔT from the initial value Tai is calculated as the assist torque correction value Taa (therefore, the steering reaction force is the initial value). Greater than the value). On the other hand, when the steering characteristic is determined to be understeer, a value obtained by adding a predetermined correction amount ΔT to the initial value Tai is calculated as the assist torque correction value Taa (therefore, the steering reaction force is smaller than the initial value). Become). When the assist torque is corrected, the output control of the first electric motor 23 is performed based on the assist torque correction value Taa, and the assist torque according to need is applied to the steering system. .

  As described above, according to the present embodiment, in the steering apparatus 10 that employs the steer-by-wire mechanism, the same effect as that of the first embodiment can be obtained. Further, by adopting the steer-by-wire mechanism, a lever-type input device, a so-called joystick, a pedal-type input device, or the like can be widely used as the handle 6, and the degree of freedom in vehicle design can be improved. .

  In each of the above-described embodiments, the front-wheel steering type vehicle has been described. However, the present invention can be similarly applied to a vehicle whose steering wheels are rear wheels or front and rear wheels. In each of the above-described embodiments, an electric motor has been described as an example of an actuator that applies assist torque to a steering system. However, the present invention is not limited to this, and a known technique such as a hydraulic mechanism is applied. be able to.

  Moreover, in each embodiment, although the detection part 18 is a structure which detects the acting force which acts on three directions as an acting force, this invention is not limited to this, Necessary component force direction It is sufficient if the acting force acting on the sensor can be detected. Further, a six-component force meter that detects a six-component force including moments around these three directions may be used. Even with such a configuration, there is no problem as a matter of course, since at least the acting force required in the control can be detected. In addition, about the method of detecting the six component force which acts on the wheel 5, since it is disclosed by Unexamined-Japanese-Patent No. 2002-039744 and Unexamined-Japanese-Patent No. 2002-022579, please refer if necessary.

  Moreover, although the case where the detection part 18 was embed | buried under the axle shaft 4 was demonstrated, this invention is not limited to this, Other variations are also considered. From the viewpoint of detecting the acting force, for example, the detection unit 18 may be provided on a member that holds the wheel 5, such as a hub or a hub carrier. In addition, since the method of providing the detection unit 18 in a hub or the like is disclosed in Japanese Patent Application Laid-Open No. 2003-104139, refer to it if necessary.

Explanatory drawing of the vehicle to which the steering apparatus concerning 1st Embodiment was applied. Block configuration diagram of a steering apparatus including a control unit Explanatory drawing of acting force acting on wheel The flowchart which shows the control routine of a steering device Explanatory drawing of the vehicle to which the steering device concerning 2nd Embodiment was applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 2 Automatic transmission 3 Center differential device 4 Axle 5 Wheel 6 Handle 10 Steering device 11 Electric motor 12 Control unit 12a Processing part 12b Control part 13 Steering shaft 14 Pinion shaft 15 Rack 16 Tie rod 17 Ring gear 18 Detection part 19 Torque sensor 20 Torsion bar 21 Vehicle speed sensor 22, 25 Power transmission mechanism 23, 24 Electric motor 26 Handle angle sensor 27 Steering angle sensor 28 Road reaction force sensor

Claims (4)

In the steering device,
With each of the front wheels and the rear wheels as detection targets, a detection unit that directly detects the lateral force acting on the wheels,
An actuator for transmitting an operation amount of a steering wheel operated by a driver to the wheel, an actuator for applying assist torque to the steering system;
A processing unit for correcting the assist torque applied to the steering system based on the lateral force acting on the front wheel and the lateral force acting on the rear wheel;
And a control unit that controls the actuator based on the corrected assist torque. A torque sensor for detecting a steering torque applied to the steering system by a steering operation of the driver;
A vehicle speed sensor for detecting the vehicle speed;
The steering device according to claim 1, wherein the processing unit sets an initial value of the assist torque as a correction target based on the detected vehicle speed and the identified steering torque.   The processing unit estimates a change in yaw rate generated in the vehicle by comparing the lateral force acting on the front wheel and the lateral force acting on the rear wheel, and determines the estimated change in yaw rate. The steering device according to claim 2, wherein the initial value of the assist torque is corrected accordingly.   When the steer characteristic is determined to be oversteer based on the estimated change in the yaw rate, the processing unit corrects the assist torque to be smaller than the initial value, and determines the estimated yaw rate. 4. The steering device according to claim 3, wherein when the steering characteristic is determined to be understeer based on a change, the assist torque is corrected to be larger than the initial value. 5.

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