JP5056162B2 - Control device for electric power steering device - Google Patents

Description

  The present invention relates to a control device for an electric power steering device in which a steering assist force by a motor is applied to the steering of a vehicle, and more particularly, to control a high performance electric power steering device that reduces the hitting noise at the rack end. Relates to the device.

  An electric power steering device that assists a vehicle steering device with an auxiliary load by the rotational force of a motor assists the steering shaft or rack shaft with a transmission mechanism such as a gear or a belt via a speed reducer. The load is energized. Such a conventional electric power steering apparatus performs feedback control of motor current in order to accurately generate assist torque (steering assist force). In the feedback control, the motor applied voltage is adjusted so that the difference between the current command value and the motor current detection value becomes small. Generally, the adjustment of the motor applied voltage is a duty of PWM (pulse width modulation) control. This is done by adjusting the tee ratio.

  Here, the general configuration of the electric power steering apparatus will be described with reference to FIG. 5. The column shaft 2 of the handle 1 is connected to the tie rod 6 of the steering wheel via the reduction gear 3, the universal joints 4 a and 4 b and the pinion rack mechanism 5. It is connected to. The column shaft 2 is provided with a torque sensor 10 that detects the steering torque of the handle 1, and a motor 20 that assists the steering force of the handle 1 is connected to the column shaft 2 via the reduction gear 3. The control unit 30 that controls the electric power steering apparatus is supplied with electric power from the battery 14 and also receives an ignition signal via the ignition key 11, and the control unit 30 detects the steering torque T and the torque detected by the torque sensor 10. A steering assist command value I of the assist command is calculated based on the vehicle speed V detected by the vehicle speed sensor 12, and a current supplied to the motor 20 is controlled based on the calculated steering assist command value I.

  The control unit 30 is mainly composed of a CPU (including an MPU and MCU). FIG. 6 shows general functions executed by a program inside the CPU.

  The function and operation of the control unit 30 will be described with reference to FIG. 6. The steering torque T detected by the torque sensor 10 and the vehicle speed V from the vehicle speed sensor 12 are input to the steering assist command value calculation unit 31. A basic steering assist command value Irefa is calculated. The vehicle speed V is further input to the convergence control unit 34 and the inertia compensation unit 35. The basic steering assist command value Irefa calculated by the steering assist command value calculation unit 31 is a phase compensation unit for increasing the stability of the steering system. The steering assist command value Irefb subjected to phase compensation at 32 and phase compensated is input to the adding unit 39A. Further, the steering torque T is input to the feedforward differential compensation unit 33 for increasing the response speed, and the differentially compensated steering torque Td is input to the addition unit 39A, where the convergence control unit 34 and the inertia compensation unit 35 The calculated compensation signal CM is also input to the adder 39A. The adding unit 39A adds the steering assist command value Irefb, the differentially compensated steering torque Td, and the compensation signal CM, and inputs the steering assist command value Irefc (= Irefb + Td + CM) as a result of the addition to the subtracting unit 39B.

  The subtraction unit 39B obtains a deviation (Irefc-Im) between the steering assist command value Irefc and the motor current Im fed back. The deviation (Irefc−Im) is PI-controlled by the PI control unit 36 and further input to the PWM control unit 37 to calculate the duty, and the motor 20 is PWM driven via the inverter 38. The motor current Im of the motor 20 is detected by the motor current detector 21, and is input to the subtractor 39B and fed back. Further, the motor 20 is provided with a rotation angle detection unit 22, and the output θ of the rotation angle detection unit 22 is input to the angular velocity calculation unit 23, and the calculated angular velocity (steering speed) ω is input to the convergence control unit 34. At the same time, it is input to the angular acceleration calculation unit 24 to calculate the angular acceleration * ω. The angular acceleration * ω is input to the inertia compensation unit 35.

  As shown in FIG. 7, the steering assist command value calculator 31 calculates and outputs a steering assist command value Irefa according to the steering torque T using the vehicle speed V as a parameter. The convergence control unit 34 is controlled by the vehicle speed V and the motor angular speed ω, and the inertia compensation unit 35 calculates an inertia compensation signal by the vehicle speed V and the motor angular acceleration * ω.

  In such an electric power steering apparatus, hitting noise is generated at the time of rack end abutment, and the noise gives the driver an unpleasant feeling. That is, the steering mechanism is configured such that when the steering wheel reaches a predetermined maximum steering angle, the steering wheel cannot be steered any further. Nevertheless, in the conventional power steering device, even if the steering wheel is steered to the vicinity of the maximum turning angle, a large steering assist force is applied to the steering mechanism if the steering torque applied to the steering wheel is large. The impact when the steering of the steering wheel is restricted is large, and there is a problem that makes the driver uncomfortable. In addition, if the impact when the steering of the steering wheel is restricted is large, there is a risk that the parts constituting the steering mechanism may be damaged.

As a device for solving such a problem, there is a control device for an electric power steering device disclosed in, for example, Japanese Patent Laid-Open No. 2002-193120 (Patent Document 1). In the apparatus of Patent Document 1, the impact that occurs when steering of the steering wheel is restricted by the maximum steering angle is reduced. That is, an electric power steering device that assists steering by applying a driving force generated by an electric motor to a steering mechanism, the steering torque detecting means for detecting the steering torque input to the steering mechanism, and the steering mechanism when the vehicle is traveling straight ahead A neutral state detecting means for detecting that the neutral state is established, and an integrated value of the steering torque detected by the steering torque detecting means after the neutral state of the steering mechanism is detected by the neutral state detecting means. A torque integrating means, a motor command current setting means for setting a motor command current to be supplied to the electric motor based on the steering torque detected by the steering torque detecting means and the integrated value of the steering torque obtained by the torque integrating means; It has.
JP 2002-193120 A

  However, since the control device of Patent Document 1 does not consider road surface friction or vehicle weight, there is a problem that the hitting noise caused by the rack end butting cannot be reliably reduced by the road surface or the vehicle. That is, in order to generate a hitting sound due to the rack end butting, it is necessary to generate an assist torque that overcomes the frictional force with the road surface determined by the tire, road surface friction and vehicle weight, and the road surface frictional force. The larger the difference between the assist torque and the assist torque (road friction force ≦ assist torque), the greater the rack end sound. For this reason, even if parameters are set under certain conditions (road surface friction and vehicle weight), if there is a difference between the road surface friction force and the assist torque due to environmental changes, the rack end abutting sound also changes. For example, in the case of a road surface with very low friction such as ice, the road surface ≦ assist torque, and the hitting sound of the rack end butting also increases.

  The present invention has been made under the circumstances as described above, and the object of the present invention is more reliable by reliably reducing the hitting noise caused by the rack end butting in any road surface condition or vehicle. An object is to provide an electric power steering apparatus.

The present invention calculates a current command value of a motor that applies a steering assist force to a steering mechanism based on a steering torque and a vehicle speed, and controls the electric power steering device that controls the drive of the motor by feedback control. With respect to the apparatus, the object of the present invention is to provide a vehicle speed sensitive gain table that outputs a gain G1 corresponding to the vehicle speed, a steering speed sensitive gain table that outputs a gain G2 corresponding to the steering speed, and a gain G3 corresponding to the steering angle. A steering angle sensitive gain table that outputs, a SAT sensitive gain table that outputs a gain G4 corresponding to the estimated SAT value, and a gain computing unit that computes a set gain based on the gains G1 to G4. The gain G1 of the gain table is a value close to “1” when the vehicle speed is zero, low at a low speed, and above a predetermined speed. “1”, the gain G2 of the steering speed sensitive gain table is set to “1” when the steering speed is slow, and decreases at a predetermined speed or more, and the gain G3 of the steering angle sensitive gain table is the rack end. It is “1” until the front, and decreases at a predetermined steering angle or more, and the gain G4 of the SAT sensitivity gain table is a characteristic that linearly increases from negative to “1” until the SAT estimated value reaches a predetermined value. When the value is larger than the predetermined value, the characteristic is “1”, the steering angle is equal to or greater than the set rack end vicinity angle, and the gain G1 to G4 is set to the gain when the estimated SAT value is equal to or less than a set value. This is achieved by causing the motor to output a steering assist torque in a direction opposite to the steering torque based on the set gain multiplied by the gain calculation unit .

  According to the control device for the electric power steering apparatus of the present invention, the set gain is calculated in consideration of the road surface condition and the vehicle weight, and the output of the steering assist motor is limited. The hitting noise at the rack end can be reduced. Moreover, the hitting noise is reduced by outputting the steering assist motor in reverse to the steering torque depending on the situation and actively performing the reverse assist. Thereby, the hitting noise at the time of a rack end can be reduced, and a high-performance electric power steering device can be provided.

  In the present invention, near the rack end, the assist of the motor is limited by limiting the output of the motor or the reverse assist is performed by reversely outputting the motor, so that the hitting noise of the hitting noise can be reduced. In addition, since the motor output is limited or reversed based on the steering angle, steering speed, vehicle speed, and SAT (self-aligning torque) estimated value, the hitting noise is ensured depending on the road surface condition and the vehicle. Can be reduced. Further, since the reverse assist that outputs the steering assist torque in the direction opposite to the input steering torque is performed based on the estimated SAT value, it is possible to actively reduce the hitting noise.

  Hereinafter, an embodiment of the present invention will be described with reference to FIG.

  FIG. 1 shows a configuration example of a control device according to the present invention corresponding to FIG. 6, and calculates a set gain GS based on a vehicle speed V, a steering speed (angular speed) ω, a steering angle θ, and a SAT estimated value * SAT. And a multiplication unit 50 that multiplies the steering torque T by the setting gain GS and inputs it to the steering assist command value calculation unit 31. The vehicle speed V is obtained from a vehicle speed sensor 12 or a CAN (Controller Area Network), the steering angle θ is obtained from a steering angle sensor or a steering angle estimation, and the steering speed ω is a rotation angle sensor attached to the motor 20 or a steering angle θ. Obtained by differentiation or obtained from the back electromotive force of the motor 20, the SAT estimated value * SAT is calculated as shown in, for example, Japanese Patent Application Laid-Open No. 2002-369565, such as motor rotational angular velocity, motor rotational angular acceleration, steering assist force, and Estimated by steering torque. In the example of FIG. 1, the steering speed ω is obtained by the rotation angle detector 22 and the angular velocity calculator 23.

  The gain setting unit 40 has the configuration shown in FIG. 2, and a vehicle speed sensitive gain table 41 that outputs a gain G1 corresponding to the vehicle speed V and a steering speed sensitive gain table that outputs a gain G2 corresponding to the steering speed ω. 42, a steering angle sensitive gain table 43 that outputs a gain G3 corresponding to the steering angle θ, a SAT sensitive gain table 44 that outputs a gain G4 corresponding to the SAT estimated value * SAT, and the gains G1 to G4. The gain calculating unit 45 is configured to calculate the gain GS.

  The vehicle speed sensitive gain table 41 sets the gain G1 to a value close to “1” because the friction between the tire road surfaces is high when the vehicle speed V is zero, and the gain G1 is set low because the frictional force is low at low speeds. Since the reaction force from the road surface increases as V increases, the gain G1 is set to “1”. The steering speed sensitive gain table 42 sets the gain G2 to “1” when the steering speed ω is slow, so that the hitting noise is more likely to occur as the steering speed ω is faster. Thus, the gain G2 is decreased. Further, since the hitting noise is a sound of the mechanism colliding at the rack end, the gain G3 is decreased from the front of the rack end (steering angle θr) in the steering angle sensitive gain table 43. Further, the SAT sensitivity gain table 44 sets the gain G4 to “1” when the SAT estimated value * SAT is larger than the predetermined value Sr, that is, when the frictional force between the road surface and the tire is large, and the SAT estimated value * SAT is small. That is, when the frictional force between the road surface and the tire is small, a negative gain is set, and the brake is applied by actively driving the motor in the reverse direction. For example, under conditions where the road surface friction is low, such as on ice, simply lowering the gain cannot absorb energy during steering, and hitting noise occurs.

When the steering angle θ is equal to or larger than the set rack end vicinity angle θr and the SAT estimated value * SAT is equal to or smaller than the set value Sr, the gain calculating unit 45 multiplies the gains G1 to G4 and sets the gain according to (1) below. Find GS.

GS = G1 × G2 × G3 × G4 (1)

With such a configuration, an example of the operation will be described with reference to the flowchart of FIG.

  First, the gain G3 is read from the steering angle sensitive gain table 43 and input (step S1), and it is determined whether or not the gain G3 is “1” (step S2). If the gain G3 is “1”, the setting is made. The gain GS is set to “1” (step S10).

  If the gain G3 is not “1” in step S2, the gain G4 is read from the SAT sensitive gain table 44 and input (step S3), and it is determined whether the gain G4 is “1” (step S4). If the gain G4 is “1”, the set gain GS is set to “1” (step S10).

  If the gain G4 is not "1" in step S4, the gain G1 is read and input from the vehicle speed sensitive gain table 41 (step S5), and further the gain G2 is read and input from the steering speed sensitive gain table 42 (step S5). S6). When the gains G1 to G4 are input in this way, the gain calculation unit 45 obtains the set gain GS by the above equation (1) (step S7).

The set gain GS is input to the multiplication unit 50 and multiplied by the steering torque T.

Ta = T × GS (2)

The steering torque Ta obtained by the above equation (2) is input to the steering assist command value calculation unit 31, and the same assist as described above is executed.

  According to the present invention, the steering torque Ta is corrected by the gain setting unit 40 with the set gain GS calculated based on the steering angle θ, the steering speed ω, the vehicle speed V, and the SAT estimated value * SAT. The hitting sound can be reduced by reducing the control system gain in the vicinity. That is, when the steering angle θ is near the rack end and the steering speed ω is faster than the predetermined speed ωr, the input value Ta of the steering torque T is reduced (the assist force of the motor is reduced, and the relationship of road surface friction force ≧ assist force). SAT estimated value * SAT for estimating the reaction force from the tire, and in the case of a road surface with low friction such as ice, the control system gain is obtained by the inertial force of the handle 1, the motor 20, the tire, etc. If the SAT estimated value * SAT is small, the brake is applied to assist in the opposite direction to the steering torque T, and the rack end hitting is reduced. Increases the ting noise reduction effect. Further, when the frictional force is high due to tires, vehicle weight, and road surface friction, the SAT estimated value * SAT increases, so that the steering torque Ta is returned to the normal state, that is, the steering torque T.

  In the above-described embodiment, the motor output is limited by multiplying the steering torque T by the set gain GS. However, even if any of the steering assist command values Irefa, Irefb, Irefc, and Iref is multiplied by the set gain GS. Similar effects can be obtained.

  As shown in FIG. 4, the same effect can be obtained by multiplying the motor current value Im detected and fed back by the motor current detection unit 21 by the gain 1 / GS, that is, increasing the motor current value Im. be able to. That is, as shown in FIG. 4, the setting gain GS obtained by the gain setting unit 40 is converted into gain 1 / GS by the conversion unit 51, the gain 1 / GS is multiplied by the motor current Im by the multiplication unit 52, and the multiplication is performed. The result Ima is fed back to the subtraction unit 39B. Since the set gain GS is “1” or less, Ima ≧ Im.

It is a block diagram which shows the structural example of the control apparatus which concerns on this invention. It is a block diagram which shows the structural example of a gain setting part. It is a flowchart which shows the operation example of this invention. It is a block diagram which shows the other structural example of the control apparatus which concerns on this invention. It is a figure which shows the general structural example of an electric power steering apparatus. It is a block diagram which shows the structural example of a control unit. The calculation characteristic of a steering assistance command value calculating part is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Handle 2 Column shaft 3 Reduction gear 10 Torque sensor 12 Vehicle speed sensor 14 Battery 20 Motor 21 Motor current detection part 22 Rotation angle detection part 23 Angular speed calculation part 30 Control unit 31 Steering assistance command value calculation part 32 Phase compensation part 33 Differential compensation part 34 Convergence control unit 35 Inertia compensation unit 36 PI control unit 37 PWM control unit 38 Inverter 40 Gain setting unit 41 Vehicle speed sensitive gain table 42 Steering speed sensitive gain table 43 Steering angle sensitive gain table 44 SAT sensitive gain table 45 Gain calculating unit 51 Conversion unit 50, 52 Multiplication unit

Claims (1)

In a control device for an electric power steering device that calculates a current command value of a motor that applies a steering assist force to the steering mechanism based on the steering torque and the vehicle speed, and drives and controls the motor by feedback control.
A vehicle speed sensitive gain table that outputs a gain G1 according to the vehicle speed, a steering speed sensitive gain table that outputs a gain G2 according to the steering speed, a steering angle sensitive gain table that outputs a gain G3 according to the steering angle, and SAT A SAT sensitive gain table that outputs a gain G4 corresponding to the estimated value; and a gain calculator that calculates a set gain based on the gains G1 to G4.
The gain G1 of the vehicle speed sensitive gain table is a value close to “1” when the vehicle speed is zero, is low when the vehicle speed is low, and is “1” when the vehicle speed is equal to or higher than a predetermined speed. The gain G2 of the steering speed sensitive gain table is When the steering speed is slow, it is set to “1” and decreases at a predetermined speed or higher. The gain G3 of the steering angle sensitive gain table is “1” until the rack end, and decreases at a predetermined steering angle or higher. The gain G4 of the SAT sensitivity gain table is a characteristic that linearly increases from negative to “1” until the SAT estimated value reaches a predetermined value, and is a characteristic of “1” when the SAT estimated value is larger than the predetermined value.
When the steering angle is equal to or greater than the set rack end vicinity angle and the SAT estimated value is equal to or less than a set value, the gain is calculated based on the set gain obtained by multiplying the gains G1 to G4 by the gain calculation unit. A control device for an electric power steering device , wherein a steering assist torque is output in a direction opposite to the steering torque .

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