JP4872378B2 - 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 is applied to a steering system of an automobile or a vehicle by driving a motor, and more particularly, a high performance electric motor designed to reduce hitting noise at a rack end. The present invention relates to a control device for a power steering device.

  An electric power steering device that assists an automobile or a vehicle steering device with an auxiliary load by the rotational force of a motor is a steering shaft or rack that transmits the driving force of the motor by a transmission mechanism such as a gear or a belt via a reduction gear. An auxiliary load is applied to the shaft. 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 steering handle 1 is connected to the steering wheel via the reduction gear 3, the universal joints 4 </ b> A and 4 </ b> B, and the pinion rack mechanism 5. It is connected to the tie rod 6. The column shaft 2 is provided with a torque sensor 10 that detects the steering torque of the steering handle 1, and a motor 20 that assists the steering force of the steering handle 1 is connected to the column shaft 2 via the reduction gear 3. ing. The control unit 30 that controls the power steering device is supplied with electric power from the battery 14 and also receives an ignition key signal from the ignition key 11, and the control unit 30 detects the steering torque value T detected by the torque sensor 10. Based on the vehicle speed V detected by the vehicle speed sensor 12, the assist assist steering command value I is calculated using an assist map or the like, and the current supplied to the motor 20 based on the calculated steering assist command value I. To control.

  The control unit 30 is mainly composed of a CPU (or MPU or MCU). FIG. 6 shows general functions executed by programs in the CPU.

The function and operation of the control unit 30 will be described with reference to FIG. 6. The steering torque T detected and input 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. Thus, the 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 phase-compensated by the phase compensation unit 32 for improving the stability of the steering system, and the phase-compensated steering assist command value Irefb is supplied to the adding unit 39A. Entered. 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 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 value 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 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, the angular acceleration * ω is input to the angular acceleration calculation unit 24 and calculated. 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 velocity, and the inertia compensation unit 35 calculates an inertia compensation signal by the vehicle speed V and the motor angular acceleration.

  In such an electric power steering apparatus, hitting noise is generated at the time of rack end abutment, and the noise causes discomfort to the driver, and thus reduction of the noise becomes a problem. That is, the steering mechanism is configured such that when the steering angle of the steering wheel reaches a predetermined maximum steering angle, the steering wheel cannot be steered any further. Nevertheless, in the conventional power steering apparatus, even if the steering wheel is steered to the vicinity of the maximum steering angle, a large steering assist force is applied to the steering mechanism if the steering torque applied to the steering handle is large. For this reason, there is a problem in that the impact when the steering of the steering wheel is restricted is large, and the driver feels uncomfortable. Moreover, if the impact when the steering of the steering wheel is restricted is large, there is a possibility that the parts constituting the steering mechanism may be damaged.

As an apparatus for reducing the hitting noise at the rack end, there is an apparatus disclosed in Japanese Patent Laid-Open No. 2002-193120 (Patent Document 1). The device described in Patent Document 1 integrates the steering torque applied to the steering wheel after the steering neutral state is detected by the torque integrating unit, and if the integrated value integrated by the torque integrating unit is outside the predetermined range, the steering is performed. By determining that the wheel is being steered to the vicinity of the maximum turning angle, setting the assist current limit in the assist current limit setting unit, and subtracting the assist current limit from the assist current determined by the assist current setting unit A motor command current is determined, and the motor is driven and controlled based on the motor command current.
JP 2002-193120 A

  However, since the conventional control device does not take into consideration the friction of the road surface and the weight of the vehicle, there is a problem that the hitting noise cannot be reliably reduced depending on the road surface condition and the vehicle. That is, in order to generate a hitting sound at the rack end, an assist force that overcomes the friction force with the road surface determined by the tire, vehicle weight, and road surface friction must be generated, and the road surface friction force and assist force must be generated. The greater the force difference (road friction force ≦ assist force), the greater the rack end hitting sound. For this reason, even if the parameters are set under certain conditions (vehicle weight or road surface friction), if a difference occurs between the road surface friction force and the assist force due to an environmental change, the rack end hitting sound also changes. For example, in the case of a road surface with very low friction such as ice, the road surface friction force ≦ assist force, and the hitting sound also increases.

  The present invention has been made under the circumstances as described above, and an object of the present invention is to control an electric power steering apparatus that can reliably reduce hitting noise at the time of a rack end regardless of road surface conditions or vehicles. To provide an 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 limiting the steering assist force by the set gain multiplied by the gain calculation unit .
The object of the present invention is to limit the steering assist force by multiplying the current command value of the motor by the set gain, or to use the limit of the steering assist force for feedback control of the motor. This is achieved more effectively by multiplying the motor current by the set gain .

  According to the control device for the electric power steering apparatus of the present invention, the setting gain is calculated in consideration of the road surface condition and the vehicle weight, so that the hitting noise at the rack end can be surely caused by any road surface condition and the vehicle. Can be reduced. Thereby, a steering feeling can be improved and a high-performance electric power steering apparatus can be provided.

  In the present invention, since the steering assist force or the current command value for driving the motor is limited near the rack end, the hitting noise of the hitting noise can be reduced. In addition, since the steering assist force or current command value is limited based on the steering angle, steering speed, vehicle speed, and SAT estimated value, it is possible to reliably reduce hitting noise depending on any road surface condition and vehicle. it can.

Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows a configuration example of a control device according to the present invention corresponding to FIG. 6, and is based on a vehicle speed V, a steering speed (angular speed) ω, a steering angle θ, and a SAT (self-aligning torque) estimated value * SAT. A gain setting unit 40 that calculates the set gain GS, and a multiplication unit 50 that multiplies the steering torque T by the set gain GS and inputs the result to the steering assist command value calculation unit 31. The vehicle speed V is obtained from a vehicle speed sensor or CAN (Controller Area Network), the steering angle θ is obtained from a steering angle sensor or steering angle estimation attached to the motor, and the steering speed ω is a rotation angle sensor or steering attached to the motor. Obtained by differentiating the angle θ, or obtained from the back electromotive force of the motor, the SAT estimated value * SAT is obtained by, for example, steering speed ω, steering angular speed, steering assist force and steering assist force as shown in JP-A-2002-369565. It is estimated from the steering angle θ. 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 frictional force 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 the vehicle speed 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. In addition, 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. In other words, when the frictional force between the road surface and the tire is small, a negative gain is set, and the motor is driven in the reverse direction to apply the brake. 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.

The gain calculation unit 45 multiplies the gains G1 to G4 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, and is set according to (1) below. The gain GS is obtained.

GS = G1 × G2 × G3 × G4 (1)

In 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 set gain is obtained. 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 that estimates the reaction force from the tire is used, and the SAT estimated value * SAT is small for roads with low friction such as ice. multiply. 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 steering assist force is limited by multiplying the steering torque T by the set gain GS. However, any of the steering assist command values Irefa, Irefb, Irefc, and Iref is multiplied by the set gain GS. The same effect 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 by the gain 1 / GS, that is, by increasing the motor current value Im. Can do. That is, as shown in FIG. 4, the setting gain GS obtained by the gain setting unit 40 is converted to gain 1 / GS by the conversion unit 52, and the gain 1 / GS is multiplied by the motor current value Im by the multiplication unit 52. The multiplication 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. It is a figure which shows the example of the calculation characteristic of a steering assistance command value calculating part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steering 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 assist command value calculation part 32 Phase compensation part 33 Differential compensation Unit 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 gain table 43 steering angle gain table 44 SAT gain table 45 gain calculation unit 51 conversion unit 50, 52 multiplier

Claims (3)

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 not less than the set rack end vicinity angle and the SAT estimated value is not more than a set value, the steering assist force is limited by 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. The control device for an electric power steering apparatus according to claim 1, wherein the steering assist force is limited by multiplying the current command value of the motor by the set gain . The control device for an electric power steering apparatus according to claim 1 , wherein the steering assist force is limited by multiplying a motor current used for feedback control of the motor by the set gain .

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