JP2008132918A - Control unit of vehicular electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control unit of a vehicular electric power steering device capable of reliably converging the yaw motion of a vehicle and enhancing the steering feeling by removing the force (the feeling of viscosity) that may reduce the steering speed of a steering device against the will of a steering person. <P>SOLUTION: The control unit 1 computes the steering auxiliary command value I based on the steering torque T and the vehicle speed signal V, detects the motor current value i by a motor current detection circuit 19, determines the control value E of a motor 38 so that the deviation (I-i) becomes zero, and controls the driving current of a motor. In addition, a steering angle computing unit 24 computes the steering angular velocity *θ based on the motor angular velocity ω, a yaw rate differential computing unit 25 differentiates the steering angular speed *θ to compute the rate of change of the yaw rate γ of a vehicle. The rate of change is multiplied by the different value according to the result of determination of a steering state determination unit 25 by a yaw rate feedback gain changing switch 263 and fed back to a subtractor 31. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a control device for an electric power steering device for a vehicle that applies a steering assist force by a motor to a steering system of a vehicle such as an automobile, and more particularly to an electric power steering for a vehicle that can ensure the convergence of the yaw rate of the vehicle. The present invention relates to an apparatus control device.

  In an electric power steering apparatus for a vehicle that assists the steering of a steering wheel by applying a steering assist force to the steering apparatus by the rotational force of the motor, the driving force of the motor is transmitted to a reduction mechanism and a transmission mechanism such as a gear or a belt. To the steering shaft or the rack shaft. Such an electric power steering device for a vehicle performs feedback control of motor current in order to accurately generate assist torque (steering assist force). This feedback control is to control the applied voltage of the motor so that the difference between the current control value and the motor current detection value is small, and is generally performed by adjusting the duty ratio in PWM (pulse width modulation) control. Yes.

Here, a conventional vehicle electric power steering apparatus will be described with reference to FIGS.
FIG. 6 is a diagram showing a general schematic configuration of a conventional vehicle electric power steering apparatus. In the electric power steering apparatus for a vehicle, as shown in FIG. 6, the shaft 32 of the steering wheel 31 is coupled to a wheel tie rod 36 via a reduction gear 33, universal joints 34 a and 34 b, and a rack and pinion 35. A torque sensor 37 that detects the steering torque of the steering wheel 31 is attached to the shaft 32, and a motor 38 that assists the steering force of the steering wheel 31 is coupled via the reduction gear 33.

  A control unit (ECU) 50, which is a conventional control device for an electric power steering device for a vehicle, is supplied with electric power from a battery 39 via an ignition key 40, and a steering torque signal T detected by a torque sensor 37 and a vehicle speed. Based on the vehicle speed signal V detected by the sensor 41, the steering assist command value I of the assist command is calculated, and a current for driving the motor 38 based on the steering assist command value I (corresponding to the motor output torque). ) To control.

  The control unit 50 mainly includes a CPU, a ROM, a RAM, an interface circuit, and the like, and controls the vehicle electric power steering apparatus by executing a program stored in the system. Here, a schematic configuration of the control unit 50 will be described with reference to FIG.

  As shown in FIG. 7, the steering torque signal T detected by the torque sensor 37 is phase-compensated by the phase compensator 51 in order to improve the stability of the steering system, and the phase-compensated steering torque signal TA is the steering assist command value. It is input to the calculator 52. The vehicle speed signal V detected by the vehicle speed sensor 41 is also input to the steering assist command value calculator 52. The steering assist command value calculator 52 determines a steering assist command value (current control target value) I for driving the motor 38 based on the input steering torque signal TA and the vehicle speed signal V detected by the vehicle speed sensor 41. To do. The steering assist command value I is input to the subtracter 53 and also input to the feedforward differential compensator 54. The differential compensator 54 increases the response speed of the control system.

  The deviation (I−i) output from the subtractor 53 is input to the proportional calculator 55 and the integral calculator 56, and both the proportional output and the integral output are input to the adder 57. Here, the integration calculator 56 is for improving the characteristics of the feedback system. The current control value E output from the adder 57 is input to the motor drive circuit 58 as a motor drive signal, and generates a drive current i for the motor 38. As a result, the motor 38 is supplied with the driving current i and transmits a steering assist force to the steering device to realize steering assistance. The drive current i is detected by a motor current detection circuit 59, and the detected motor current value i is fed back to the subtractor 53.

  FIG. 8 is a diagram showing a schematic configuration of the motor drive circuit 58. As shown in FIG. 8, the motor drive circuit 58 includes field effect transistors FET1 to FET4 constituting an H bridge circuit, and FET gates for driving the gates of the FET1 to FET4 based on the current control value E sent from the adder 57. A drive circuit 581, a boost power source 582 that drives the high side of the FETs 1 and 2, and resistance elements R 1 and R 2 inserted between the ground and the FETs 3 and 4 for detecting a current flowing through the motor 38. Yes.

The FETs 1 and 2 are turned on / off by a PWM (pulse width modulation) signal having a duty ratio D 1 determined based on the current control value E, and control the magnitude of the current i that actually flows through the motor 38. The FETs 3 and 4 are driven by a PWM signal having a duty ratio D2 defined by a predetermined linear function formula D2 = a · D1 + b (where a and b are constants) in a region where the duty ratio D1 is small. After reaching 100%, it is turned ON / OFF according to the rotation direction of the motor 38 determined by the sign of the PWM signal.

  In the control apparatus for an electric power steering apparatus for a vehicle as described above, as an example in which an appropriate response is generated when a steering person operates the steering apparatus rapidly, the change rate of the yaw rate of the vehicle is detected and detected. There is known one in which damping is imparted to the yaw rate based on the rate of change (see, for example, Patent Document 1).

  And a means for compensating steering system damping (viscous friction) based on a signal obtained by extracting a high frequency component of the angular velocity of the motor, and a means for determining a steering state based on the steering torque signal and the motor angular velocity. In some cases, the characteristic of the viscous friction compensation value is switched in accordance with (see, for example, Patent Document 2).

JP 2000-95132 A Japanese Patent No. 3527469

  However, in the control device for the electric power steering device for a vehicle described in Patent Document 1 described above, the same damping is always applied to the yaw rate, and the yaw rate damping control can be performed even when the steering device is increased. Will work. As a result, contrary to the intention of the steering wheel, there is a possibility of feeling a force that reduces the steering speed of the steering device (viscosity) and feeling that the steering feeling is impaired, and there is room for improvement.

  On the other hand, in the control device for the electric power steering device for a vehicle described in Patent Document 2, the characteristic of the viscous friction compensation value is switched according to the steering state, so that the damping control is performed according to the turning-up state and the switching-back state of the steering device. Although it functions, it does not take into account the rate of change of the yaw rate, so there is a problem in terms of steering feeling.

  The present invention has been made in view of the above circumstances, and its purpose is to reliably converge the yaw motion of the vehicle without impairing the intention of the steering wheel and to improve the steering feeling. Another object of the present invention is to provide a control device for an electric power steering device for a vehicle.

  In order to achieve the above-described object, a control device for an electric power steering device for a vehicle according to the present invention is characterized by the following (1) to (3).

(1) The motor output torque is controlled based on the steering assist command value calculated based on the steering torque generated on the steering shaft and the current control value calculated based on the current value of the motor. In a control device for an electric power steering device for a vehicle that applies a steering assist force,
A yaw rate change rate detecting means for detecting a change rate of the yaw rate of the vehicle;
Steering state determination means for determining the steering state of the steering mechanism,
Damping is applied to the yaw rate based on the rate of change of the yaw rate detected by the yaw rate change rate detecting means and the steering state of the steering device determined by the steering state determining means.
(2) In the control device for an electric power steering device for a vehicle according to the above (1),
A yaw rate feedback gain switching means for switching a feedback gain value by which the yaw rate change rate detected by the yaw rate change rate detection means is multiplied;
The yaw rate feedback gain switching means is
The feedback gain value is switched based on the steering state of the steering device determined by the steering state determination means, and the feedback gain value is multiplied by the yaw rate change rate detected by the yaw rate change rate detection means for output. The output is fed back to the motor output torque to give damping to the yaw rate.
(3) In the control device for an electric power steering device for a vehicle according to (1) or (2),
The steering state determination means includes
The present invention is characterized in that it determines whether the steering device is in an increased state or a switched back state.

  According to the present invention, it is possible to remove a force (viscosity) that decreases the steering speed of the steering device against the intention of the steering operator, to surely converge the yaw motion of the vehicle, and to improve the steering feeling. It is possible to provide a control device for an electric power steering device for a vehicle capable of achieving the above.

  Hereinafter, embodiments of a control device for an electric power steering device for a vehicle according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of a control device for an electric power steering device for a vehicle according to an embodiment of the present invention. In addition, description of the part which is common in the structure demonstrated in FIGS. 6-8 mentioned above is simplified or abbreviate | omitted by attaching | subjecting the same code | symbol or an equivalent code | symbol.

  As shown in FIG. 1, a control unit 1 that is a control device for an electric power steering device for a vehicle includes a phase compensator 51, a steering assist command value calculator 52, a subtractor 13, a differential compensator 54, and a proportional unit. A computing unit 55, an integral computing unit 56, an adder 57, a motor drive circuit 58, a motor current detection circuit 59, a motor angular velocity estimator 20, a loss torque compensator 21, a motor angular acceleration estimator 22, An inertia compensator 23, a steering angular velocity calculator 24, a yaw rate differential calculator 25, a convergence controller 26, and a steering state determiner 27 are provided. In addition, for example, an A / D converter (not shown) is used so that signals inputted from the outside such as the steering torque signal T and the vehicle speed signal V inputted to the control unit 1 can be appropriately processed by the control unit 1. It is converted from an analog signal to a digital signal. The signal such as the speed signal V may be input to the control unit 1 via a digital communication line such as CAN mounted on the vehicle. Further, these signals are amplified by an amplifier (not shown), and subjected to a filtering process as appropriate by a low-pass filter (not shown).

  The motor angular velocity estimator 20 receives the current detection value i output from the motor current detection circuit 59 and the current control value E output from the adder, and receives the current detection value i and the current control value. The motor angular velocity ω is estimated from E, and the result is output to the loss torque compensator 21, the steering state determiner 27, the steering angular velocity calculator 24, and the motor angular acceleration estimator 22.

  The loss torque compensator 21 compensates for the loss torque of the motor 38 caused by backlash or circuit heat generation of the reduction gear 33, and the direction in which the loss torque is generated, that is, the rotation direction of the motor 38. The loss torque equivalent is compensated and output to the subtractor 13.

  The motor angular acceleration estimator 22 obtains a motor angular acceleration by performing a differential operation on the input motor angular velocity ω and outputs the motor angular acceleration to the inertia compensator 23. Based on the motor angular acceleration, the inertia compensator 23 sets the control steering assist command value I according to a change in an inertia system related to a drive system such as the steering hole 31, the pinion rack mechanism 35, the motor 38, and the reduction gear 33. Correction is made to suppress fluctuations in motor output torque. Thus, the inertia of the drive system is prevented from being transmitted to the steering person, and the steering feeling is improved.

  Further, the steering state determination unit 27 receives the steering torque signal T and the motor angular velocity ω, and determines whether the steering device is in an increased state or a switched back state based on the input. This determination result is input to a yaw rate feedback gain changeover switch 263, which will be described later, and used to switch a feedback gain that multiplies the rate of change of the yaw rate γ.

  Further, the steering angular velocity calculator 24 receives the motor angular velocity ω, calculates the steering angular velocity * θ from the reduction ratio of the reducer 33 that is known in advance, and outputs the result to the yaw rate differentiation calculator 25. . The yaw rate differential calculator 25 calculates the rate of change of the yaw rate γ of the vehicle by differentiating the steering angular velocity * θ.

  The convergence controller 26 includes a multiplication amplifier 261 that multiplies the rate of change of the yaw rate γ calculated by the yaw rate differentiation calculator 25 by a predetermined feedback gain value G1, and another predetermined feedback gain value G2 (however, , G1 <G2), and a yaw rate feedback gain switch for switching the connection to one of the increase amplifier 261 and the switchback amplifier 262 based on the determination of the steering state determination unit 27. Switch 263. That is, in the convergence controller 26, the yaw rate feedback gain changeover switch 263 performs switching based on the determination result of the steering state determiner 25, and increases when it is determined that the steering device is in the increased state. When it is determined that the switch-back state has been established, it is connected to the switch-back amplifier 262 to select and output feedback gains having different values. The feedback gain values G1 and G2 are values calculated from a preset gain and a vehicle speed signal V detected by the vehicle speed sensor 41, as will be described later.

  The signal output in this way is fed back to the subtractor 13 as a convergence signal CN for converging the yaw rate, and damping is applied to the yaw rate γ according to each of the turning-up state and the returning state of the steering device. .

  Next, operation | movement of the control unit 1 which concerns on embodiment of this invention is further demonstrated according to FIGS.

  First, considering a vehicle model as shown in FIG. 2, giving damping to the yaw rate γ will be described more specifically.

The steering force of the steering wheel 31 of the steering wheel is Th, the column output value of the motor output torque generated by the motor 38 is Tm, the acceleration ratio of the rack and pinion is g, the steering inertia, the motor inertia, the reduction ratio, etc. are included. If the constant is J, the model of the automobile shown in FIG. 2 is shown in FIG. 3 as a transfer characteristic block. Here, s is a Laplace operator, and a ₁ , a ₂ , b ₀ , b ₁ , c ₀ , c ₁ , c ₂ are parameters related to the vehicle speed V.

  In FIG. 3, when the transmission characteristic from the motor output torque Tm to the yaw rate γ is obtained with the steering force Th as a minute value, it can be simplified and expressed as Expression (1).

  Furthermore, as shown in FIG. 4, when a control system that performs a predetermined feedback by feedback inputting the yaw rate γ to the motor output torque Tm, the following equation (2) is established.

  Here, assuming that the gain related to the yaw rate γ is Kd and P (s) = Kd · s / (b0 · s + b1), the equation (2) can be expressed as the following equation (3).

  Here, when the formula (3) for feeding back the yaw rate γ is compared with the formula (1), the gain Kd is newly expressed in the second term (first-order term of s) of the denominator in the formula (1). I understand that. As a result, by adjusting the gain Kd in P (s) in the transfer characteristic from the steering torque Tm to the yaw rate γ, damping according to the gain Kd can be imparted to the yaw rate γ. It can be seen that the astringency can be improved.

  Here, when further developing based on Expression (1) and Expression (3), the feedback value to the motor torque Tm can be expressed as Expression (4) as shown below.

  Therefore, it can be seen that the yaw rate γ can be damped by feeding back the rate of change of yaw rate γ (differential value of yaw rate) * γ (s) to the motor output torque Tm.

  Therefore, in the control unit 1 according to the embodiment of the present invention, a plurality of the gains Kd described above are prepared and set in advance in the switch-back amplifier 262 and the switch-back amplifier 262, respectively, and the yaw rate feedback gain switching is performed. Based on the determination result of the steering state determiner 27 by the switch 263, a different value is set depending on whether the steering wheel is actively steering the steering device or not. Thus, the yaw rate γ can be damped, and the yaw motion of the vehicle can be reliably converged and the steering feeling can be improved without hindering the intention of the steering wheel.

  Next, switching operations by the steering angular velocity calculator 24, the yaw rate differential calculator 25, the steering state determiner 25, and the yaw rate feedback gain changeover switch 263 will be described with reference to a flowchart. FIG. 5 is a flowchart for explaining the feedback gain switching operation.

  First, the steering angular velocity calculator 24 calculates the steering angular velocity * θ from the motor angular velocity ω (step S101). Note that the motor angular velocity ω and the steering angular velocity * θ have a substantially proportional relationship, and therefore the steering angular velocity * θ can be easily obtained from the motor angular velocity ω.

Next, the yaw rate differential calculator 25 calculates the rate of change of the yaw rate γ of the vehicle from the steering angular velocity * θ calculated at the steering angular velocity 24 (step S102).
In general, the relationship between the steering angle θ and the yaw rate γ is expressed by the following equation (5).

さらに、式（５）の両辺を微分すると、次の式（６）となる。

Furthermore, when both sides of the equation (5) are differentiated, the following equation (6) is obtained.

  Thus, by using the equation (6), the rate of change of yaw rate * γ (s) can be obtained from the steering angular velocity * θ (s).

  Further, since the natural frequency in the transmission characteristic of the motor output torque Tm versus the steering angle θ of the mechanical system of the steering device is about 10 times higher than the natural frequency of the steering angle θ versus the yaw rate γ, the steering torque signal T is the steering angle θ. It can be considered that it is almost proportional to. Therefore, by feeding back a signal proportional to * γ (s) in the equation (6) to the subtractor 13, a steering angle signal synchronized with the rate of change of the yaw rate γ can be generated. It can be seen that damping can be applied.

  In step S <b> 103, the steering state determination unit 25 determines whether the steering device is in the increased state or the switched back state. For this determination, a method is used in which the direction in which the steering torque T by the torque sensor 2 matches the direction of the motor angular velocity ω is set to the increased state, and the case in which the direction does not match is set to the return state.

  If it is determined in step S103 that the steering device is in the increased state, the yaw rate feedback gain changeover switch 263 is connected to the increased amplifier 261, selects the feedback gain value G1, and outputs it to the subtractor 13. .

  On the other hand, if it is determined in step S103 that the steering device is in the switchback state, the yaw rate feedback gain switching switch 263 is connected to the switchback amplifier 262, selects the feedback gain value G2, and outputs it to the subtractor 13. (Step S105).

  Therefore, according to the present embodiment, it is determined whether the steering device is in the increased state or the switched back state, and the feedback gain value is selected according to the determination result and output to the subtractor 13. It is possible to reliably perform yaw convergence, which is important in steering-hand steering of a steering device, and to remove a force (viscous feeling) that decreases the steering speed of the steering device against the intention of the steering wheel. it can.

  The description of the specific embodiments is finished above, but the aspect of the present invention is not limited to these embodiments, and modifications, improvements, and the like can be made as appropriate. For example, in the present embodiment, most of the processing is performed by software, but a part or all of the processing may be realized by hardware such as FPGA (Field Programmable Gate Array). Further, although the rate of change of the yaw rate γ is calculated using the steering angular velocity * θ, the present invention is not limited to this, and the yaw rate γ may be directly measured.

  In the present embodiment, the PID control has been described as an example. However, the present invention is not limited to this, and the present invention can be applied to various control systems such as a robust control system.

  The present invention is applicable to all electric power steering devices regardless of the type of electric power steering device (column type, pinion type, rack type) and the type of motor (with brush, brushless, etc.).

It is a block diagram showing a schematic structure of a control device of an electric power steering device for vehicles concerning an embodiment of the present invention. It is the figure which modeled the car. It is a figure which shows the model of the motor vehicle shown in FIG. 2 with a transmission characteristic block. It is a block diagram which shows the transfer characteristic including the feedback of a motor output torque and a yaw rate. It is a flowchart for demonstrating switching operation | movement of the yaw rate gain of the control apparatus of the electric power steering device for vehicles which concerns on embodiment of this invention. It is a figure which shows schematic structure of the conventional electric power steering apparatus for vehicles. It is a figure which shows the general schematic structure of the conventional control unit. It is a figure which shows the general schematic structure of a motor drive circuit.

Explanation of symbols

1,50 Control unit 24 Steering angular velocity calculator (yaw rate change rate detecting means)
25 Yaw rate differential calculator (yaw rate change rate detection means)
26 Convergence Controller 261 Increase Amplifier 262 Switchback Amplifier 263 Yaw Rate Feedback Gain Changeover Switch (Yaw Rate Feedback Gain Changeover Unit)
27 Steering state determination device (steering state determination means)
36 motor

Claims (3)

The steering assist force is applied to the steering mechanism by controlling the motor output torque based on the steering assist command value calculated based on the steering torque generated on the steering shaft and the current control value calculated based on the motor current value. In the control device for an electric power steering device for a vehicle that gives
A yaw rate change rate detecting means for detecting a change rate of the yaw rate of the vehicle;
Steering state determination means for determining the steering state of the steering mechanism,
The vehicle electric motor characterized in that damping is applied to the yaw rate based on the change rate of the yaw rate detected by the yaw rate change rate detection means and the steering state of the steering device determined by the steering state determination means. Control device for power steering device. A yaw rate feedback gain switching means for switching a feedback gain value by which the yaw rate change rate detected by the yaw rate change rate detection means is multiplied;
The yaw rate feedback gain switching means is
The feedback gain value is switched based on the steering state of the steering device determined by the steering state determination means, and the feedback gain value is multiplied by the yaw rate change rate detected by the yaw rate change rate detection means for output. The control device for an electric power steering apparatus for a vehicle according to claim 1, wherein damping is applied to the yaw rate by feeding back the output to a motor output torque. The steering state determination means includes
The control device for an electric power steering device for a vehicle according to claim 1 or 2, wherein the control device determines whether the steering device is in an increased state or a switched back state.

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