JP5007627B2 - 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 a steering system of a vehicle, and more particularly, to an electric power steering device that improves comfortable transmission of road surface information and obtains comfortable steering performance. The present invention relates to a control device.

  An electric power steering device for energizing a vehicle steering device with an auxiliary load by a rotational force of a motor applies an auxiliary load to a steering shaft or a rack shaft by a transmission mechanism such as a gear or a belt via a reduction gear. It has come to force. Such a conventional electric power steering apparatus performs feedback control of motor current in order to accurately generate assist torque (steering assist torque). 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. 6. The column shaft 2 of the steering handle 1 is connected to 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 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 outputs a torque signal Th. A motor 20 that assists the steering force of the steering handle 1 is provided via the reduction gear 3. Are connected to the column shaft 2. Electric power is supplied from the battery 14 to the control unit 100 that controls the power steering apparatus, and an ignition key signal is input through the ignition key 11. The torque signal Tr and the vehicle speed from the torque sensor 10 are input to the control unit 100. A vehicle speed signal Vel detected by the sensor 12 is input, a steering assist command value I of an assist command is calculated based on the torque signal Th and the vehicle speed signal Vel, and the motor 20 is calculated based on the calculated steering assist command value I. Control the current supplied.

  In such an electric power steering apparatus, conventionally, as shown in, for example, Japanese Patent Laid-Open No. 8-290778 (Patent Document 1), the stability of the system, road surface information, and disturbances are obtained by a robust stabilization compensator in the control unit 100. Information sensitivity characteristics are designed at the same time.

  However, in such a conventional control device, since the reaction force at the time of steering near the steering neutral point is small, it is difficult to accurately convey road surface information to the driver due to the influence of friction. Further, in the conventional electric power steering apparatus, it is difficult to make the hysteresis characteristic between the steering angle and the steering force equal to that of the hydraulic power steering.

  As an apparatus for solving such a problem, there is an apparatus disclosed in Japanese Patent Laid-Open No. 2002-369565 (Patent Document 2).

  An outline of the apparatus disclosed in Patent Document 2 will be described with reference to FIG. A motor 20 that generates an auxiliary steering force of the steering device is driven by a motor drive unit 21, and the motor drive unit 21 is controlled by a control unit 100 indicated by a two-dot chain line, and the control unit 100 includes a torque signal Tr and a torque signal Tr from a torque sensor. A vehicle speed signal Vel from the vehicle speed detection system is input. In the motor 20, the motor terminal voltage Vm and the motor current value Im are measured and output.

  The control unit 100 includes a torque system control unit 110 indicated by a broken line that performs control using the torque signal Tr, and a motor system control unit 120 indicated by an alternate long and short dash line that performs control related to driving of the motor 20. The torque system controller 110 includes an assist amount calculator 111, a differential controller 112, a yaw rate convergence controller 113, a robust stabilization compensator 114, and a self-aligning torque (SAT) estimation feedback unit 115. 116B and a subtractor 116C. The motor system control unit 120 includes a compensator 121, a disturbance estimator 122, a motor angular velocity estimation unit 123, a motor angular acceleration estimation unit (differentiator) 124, and a motor characteristic compensation unit 125, and includes adders 126A and 126B. is doing.

  The torque signal Tr is input to the assist amount calculation unit 111, the differential controller 112, the yaw rate convergence control unit 113, and the SAT estimation feedback unit 115, and all use the vehicle speed signal Vel as a parameter input. The assist amount calculation unit 111 calculates the assist torque amount Ia based on the torque signal Tr, and the yaw rate convergence control unit 113 receives the torque signal Tr and the estimated motor angular velocity value ω, and improves the yaw convergence of the vehicle. For this reason, the brake is applied to the movement of the steering wheel. Further, the differential controller 112 enhances the control response in the vicinity of the neutral point of the steering and realizes smooth and smooth steering. The SAT estimation feedback unit 115 includes the torque signal Tr and the assist amount calculation unit 111. Signal Ib obtained by adding the output of the differentiation controller 112 to the output of the adder 116A, the angular velocity estimated value ω estimated by the motor angular velocity estimating unit 123, the angular acceleration estimated value * ω from the motor angular acceleration estimating unit 124, and SAT is estimated by inputting, and the estimated SAT value is signal-processed using a feedback filter, and appropriate road surface information is given to the steering wheel as a reaction force.

  Further, the signal Ib obtained by adding the output of the differentiation controller 112 to the output Ia of the assist amount calculation unit 111 by the adder 116A and the signal obtained by adding the output of the yaw rate convergence control unit 113 by the adder 116B are robust as the assist amount AQ. This is input to the stabilization compensator 114. The robust stabilization compensator 114 is a compensator disclosed in, for example, Japanese Patent Laid-Open No. 8-290778, and removes the peak value at the resonance frequency of the resonance system including the inertia element and the spring element included in the detected torque, and performs control. It compensates for the phase shift of the resonance frequency that hinders the responsiveness and stability of the system. By subtracting the output of the SAT estimation feedback unit 115 from the output Ic of the robust stabilization compensator 114 by the subtractor 116C, an assist amount Id that can transmit road surface information to the steering wheel as a reaction force is obtained.

  Further, the motor angular speed estimation unit 123 estimates the motor angular speed ω based on the motor terminal voltage Vm and the motor current Im. The motor angular speed ω is estimated by the motor angular acceleration estimation unit 124, the yaw rate convergence control unit 113, and the SAT estimation. Input to the feedback unit 115. The motor angular acceleration estimation unit 124 estimates the motor angular acceleration * ω based on the input motor angular velocity ω, and the estimated motor angular acceleration * ω is input to the motor characteristic compensation unit 125. An assist amount Id obtained by subtracting the output SATf of the SAT estimation feedback unit 115 from the output Ic of the robust stabilization compensation unit 114 is added to the output Ima of the motor characteristic compensation unit 125 by the adder 126A, and the addition signal is a steering assist command value. Ie is input to a compensator 121 composed of a differential compensator or the like. A signal obtained by adding the output of the disturbance estimator 122 to the steering assist command value If compensated by the compensator 121 by the adder 126B is input to the motor drive unit 21 and the disturbance estimator 122. The disturbance estimator 122 is a device as disclosed in JP-A-8-310417, and the output of the disturbance estimator 122 is added to the steering assist command value If compensated by the compensator 121 that is a control target of the motor output. Based on the signal and the motor current value Im, it is possible to maintain a desired motor control characteristic in the output reference of the control system, so that the stability of the control system is not lost.

Here, the state of the torque generated between the road surface and the steering will be described with reference to FIG. A steering torque Th1 is generated when the driver steers the steering handle 1, and the motor 20 generates an assist torque Tm according to the steering torque Th1. As a result, the wheels are steered and SAT is generated as a reaction force. Further, at that time, torque serving as steering steering resistance is generated by the inertia J and friction (static friction) Fr of the motor 20. Considering the balance of these forces, the following equation of motion can be obtained:

J ・ * ω + Fr ・ sign (ω) + SAT = Tm + Th1 (1)

Here, when the above equation (1) is Laplace transformed with an initial value of zero and solved for SAT, the following equation (2) is obtained.

SAT (s) = Tm (s) + Th1 (s) − J · * ω (s) + Fr · sign (ω (s)) (2)

As can be seen from the above equation (2), the SAT is obtained from the motor rotational angular velocity ω, rotational angular acceleration * ω, steering assist force, and steering torque Th1 by obtaining the inertia J and static friction Fr of the motor 20 as constants. Can be estimated. For this reason, the SAT estimation feedback unit 115 receives the torque signal Tr, the angular velocity ω, the angular acceleration * ω, and the output Ib of the assist amount calculation unit 111. The assist torque Tm can be obtained by multiplying the output Ib of the assist amount calculation unit 111 by the gear ratio × torque constant.

Further, when the SAT information estimated by the SAT estimation feedback unit 115 is fed back as it is, the steering becomes too heavy, so that the steering feeling cannot be improved. Therefore, as shown in FIG. 9, the estimated value of SAT is signal-processed using a feedback filter 115A having a vehicle speed sensitivity gain and a frequency characteristic, and only information necessary and sufficient for improving the steering feeling is fed back. The feedback filter used here has, as a static characteristic gain, a Q filter (phase delay) 115B having a gain that reduces the estimated SAT size to a necessary and sufficient value, and a gain unit 115C that responds to the vehicle speed as shown in FIG. The road surface information to be fed back is made smaller when the importance of road surface information such as stationary driving and low speed driving is relatively low.
JP-A-8-290778 JP 2002-369565 A JP 2006-193080 A

  The SAT estimated by the device described in Patent Document 2 has a value with a response delay due to the steering transmission system, and there is a problem that a delay occurs in feedback to the driver.

  As an apparatus for solving such a problem, there is an apparatus disclosed in Japanese Patent Laid-Open No. 2006-193080 (Patent Document 3). As shown in FIG. 11, the apparatus disclosed in Patent Document 3 inputs the angular velocity ω and angular acceleration * ω of the motor, the steering assist command value Ib, and the torque signal Tr, and estimates the self-aligning torque or measures it with a sensor. A SAT estimation unit 117 is provided, and the SAT estimated value * SAT estimated by the SAT estimation unit 117 is fed back to the steering assist command value through a feedback unit 118 including a phase compensation unit and a gain unit. As shown in FIG. 12, the feedback unit 118 multiplies a phase lead compensation unit 118-1 that receives and compensates for the SAT estimated value * SAT, a low-pass filter 118-2 for removing disturbance and noise, and a gain K. And a gain unit 118-3.

  According to the apparatus described in Patent Document 3, when a low-frequency SAT necessary for the driver is appropriately fed back, more road surface information can be transmitted to the driver than when no SAT feedback is provided.

  However, although the driver feels a change in the SAT and predicts the vehicle behavior, there is a problem that the driver does not feed back the change in the SAT and is insufficient to predict the vehicle behavior.

  The present invention has been made under the circumstances as described above, and an object of the present invention is to provide a control device for an electric power steering device that makes it easy for a driver to predict vehicle behavior and obtains a safe and comfortable steering performance. There is.

  The present invention includes a steering assist command value calculation unit that calculates a steering assist command value based on a torque signal from a torque sensor, a current control unit that calculates a voltage command value based on the steering assist command value, and the voltage command A motor driving unit that drives the motor based on the value, and applies an assist force by the motor to the steering system, and the angular velocity and angular acceleration of the motor, the steering assist command value, and the torque signal Is provided with a SAT measurement unit that inputs SAT and performs measurement by a sensor, and feeds back the SAT value obtained by the SAT measurement unit to the steering assist command value. The object of the present invention is to provide a SAT change rate feedback section for calculating the change rate of the SAT value, and to provide the SAT change rate feedback. The SAT change rate calculated in parts is achieved by feeding back to the steering assist command value.

  In addition, the object of the present invention is that the SAT change rate feedback unit includes a differential operation unit and a gain unit, or that the SAT change rate feedback unit further includes a low-pass filter, or The cutoff frequency of the low-pass filter and the gain of the gain section can be changed by the vehicle speed, or the gain of the gain section can be changed by the torque signal, or the gain This is achieved more effectively by the fact that the gain of the part can be changed by the rotational speed of the motor.

  According to the present invention, the SAT estimation unit for estimating the self-aligning torque (SAT) or the SAT measurement unit for measuring by the sensor is provided, and the SAT estimation value estimated by the SAT estimation unit or the SAT measurement unit is measured. Since the change rate of the SAT value is fed back, the driver can recognize the change in the road surface information, so that the vehicle behavior can be easily predicted, and a safe and comfortable steering performance can be obtained.

  In the present invention, the rate of change of the estimated SAT value or the measured SAT value is fed back. As a result, the change in SAT is transmitted to the driver, and the steering feeling is easy for the driver to predict the vehicle behavior.

  An embodiment of the present invention will be described below with reference to FIG. 1 corresponding to FIG. The same parts as those in FIG. 11 are denoted by the same reference numerals, and description thereof is omitted.

In the present invention, the SAT estimation unit 117 estimates the SAT by inputting the torque signal Tr, the angular velocity (motor rotational speed) ω, the angular acceleration * ω, and the steering assist command value Ib that is the addition result from the adder 116A. The SAT estimated value * SAT is fed back to the subtractor 116C and fed back via the SAT change rate feedback unit 130. That is, the feedback estimated value SAT is directly subtracted and input to the subtractor 116C, and the output * SAT _{D of the} SAT change rate feedback unit 130 is also subtracted and input to the subtractor 116C.

The configuration of the SAT change rate feedback unit 130 is as shown in FIG. 2. From the differential calculation unit 131 that obtains the SAT change rate * SATd by inputting and differentiating the SAT estimated value * SAT, SAT change rate * SATd is input, and a low-pass filter 132 that cuts high-frequency components with the cutoff characteristics shown in FIG. 3 and a signal u from the low-pass filter 132 are input to input a vehicle speed signal Vel, torque signal Tr, and angular velocity ω And a gain unit 133 whose gain changes correspondingly. Therefore, the SAT change rate feedback unit 130 receives the SAT estimated value * SAT, the vehicle speed signal Vel, the torque signal Tr, and the angular velocity ω.
Note that the gain unit 133 has a function G _V (Vel) of the vehicle speed signal Vel that becomes a low gain at a low vehicle speed as shown in FIG. 4A, and a low gain at a large steering torque as shown in FIG. The function Gt (Tr) of the torque signal Tr and the function Go (ω) of the angular velocity ω whose gain increases in a linear shape according to the magnitude of the angular velocity ω as shown in FIG. The output * SAT _D is expressed by the following equation (3).

* SAT _D = u × {G _V (Vel) × Gt (Tr) × Go (ω)} (3)

In such a configuration, the SAT estimation unit 117 estimates the SAT by inputting the torque signal Tr, the angular velocity ω, the angular acceleration * ω, and the steering assist command value Ib from the adder 116A, and the estimation is described above (2 ). The estimated SAT estimated value * SAT is input to the addition / subtraction unit 116C and the SAT change rate feedback unit 130, thereby compensating for the delay in the steering transmission system and predicting the vehicle behavior.

When expressed as a transfer function, the SAT change rate feedback unit 130 differentiates the input SAT estimated value * SAT with an approximate differential expression of the following expression (4), where s is a Laplace operator and T ₁ is a time constant.

T ₁ · s / (T ₁ · s + 1) (4)

Thus, the SAT estimated value * SAT is input to the SAT change rate feedback unit 130, first differentiated by the differential compensation unit 131 according to the above equation (4), and the obtained SAT change rate * SATd is input to the low pass filter 132, After the high frequency noise component is removed, it is input to the gain unit 133. In the gain unit 133, first, the gain is adjusted with a function G _V (Vel) shown in FIG. 4A based on the vehicle speed signal Vel, and then the function Gt (Tr) shown in FIG. 4B based on the torque signal Tr. Then, the gain is adjusted with the function Go (ω) shown in FIG. 4C based on the angular velocity ω. The order of gain adjustment of the function G _V (Vel), the function Gt (Tr), and the function Go (ω) may be arbitrarily changed.

  In this way, the SAT estimated value * SAT change rate * SATd is obtained, and the gain is adjusted by the gain unit 133 via the low-pass filter 132 and fed back to the subtraction unit 116C. Since feedback is provided, the driver has the effect of facilitating the vehicle behavior, and noise passing through the low-pass filter 132 can reduce noise when obtaining the change rate * SATd.

  Further, since the cutoff frequency of the low-pass filter 132 and the gain of the gain unit 133 can be changed by the vehicle speed signal Vel as shown in FIG. 3, the noise feeling is suppressed at a low vehicle speed, and the SAT change rate at a high vehicle speed. The steering feeling can be improved by strengthening the feedback. Furthermore, since the gain of the gain unit 133 is sensitive to steering torque (torque signal) and is sensitive to angular velocity, a constant Lissajous characteristic (steering angular velocity versus steering torque or yaw rate characteristic) independent of the steering speed is obtained. This makes it easier for the driver to predict the vehicle behavior.

FIG. 5 shows an example of the configuration of the control unit 210 when the brushless motor 200 is driven. The torque signal Tr from the torque sensor 201 is input to the steering assist command value calculation unit 211, and the SAT estimation unit 230 and SAT. It is input to the change rate feedback unit 250. A vehicle speed signal Vel from the vehicle speed sensor 202 is input to the steering assist command value calculation unit 211 and also input to the SAT change rate feedback unit 250 and the convergence compensation unit 220. The steering assist command value Iref1 calculated by the steering assist command value calculation unit 211 is added to the compensation signal CM2 by the addition unit 222, and the steering assist command value Iref2 as the addition result is input to the SAT estimation unit 230 and the two-phase. Is input to a two-phase / three-phase converter 226 that converts the signal into three phases. The angle θ from the rotation sensor 217 is also input to the two-phase / three-phase conversion unit 226, and the steering assist command value Iref <b> 2 converted into three phases is input to the subtraction unit 226. The subtraction unit 223 obtains a deviation current ΔI of each phase between the steering assist command value Iref2 and the motor current Im, and uses the deviation current ΔI of each phase via the PI current control unit 212, the pulse width modulation (PWM) unit 213, and the inverter 214. Then, the brushless motor 200 is driven. The motor current Im of each phase of the brushless motor 200 to which the rotation sensor 217 is connected to the brushless motor 200 is detected by the motor current detection unit 215, input to the subtraction unit 223, and connected to the brushless motor 200. The angle θ from the rotation sensor 217 is input to the two-phase / three-phase converter 226 and also input to the angular velocity calculator 218. The angular velocity ω calculated by the angular velocity calculation unit 218 is input to the angular acceleration calculation unit 218 and also input to the convergence control unit 220, the SAT estimation unit 230, and the SAT change rate feedback unit 250. The angular acceleration * ω calculated by the angular acceleration calculation unit 218 is input to the SAT estimation unit 230 and the inertia compensation unit 221. The SAT estimated value * SAT from the SAT estimation unit 230 is input to the SAT change rate feedback unit 250 configured as described above, and also input to the addition unit 224. The SAT value * SAT _D from the SAT change rate feedback unit 250 is also input to the adder 224, added to the inertia signal Ii from the inertia compensator 221, and input to the adder 225 as the compensation signal CM1. The addition unit 225 also receives the convergence signal Ic from the convergence compensation unit 220, and the compensation signal CM2 added to the compensation signal CM1 is added to the steering assist command value Iref1 by the addition unit 222. The SAT estimation unit 230 in this example corresponds to the SAT estimation unit 117 in FIG. 1, and the SAT change rate feedback unit 250 corresponds to the SAT change rate feedback unit 130 in FIG.

  In the above-described embodiment, the SAT is estimated by the SAT estimation unit 117. However, the SAT may be obtained by measurement using a sensor.

It is a block block diagram which shows the Example of this invention. It is a block block diagram which shows the structural example of the SAT change rate feedback part used for this invention. It is a figure which shows the example of a characteristic of a low-pass filter. It is a figure which shows the example of a characteristic of a gain part. It is a block block diagram which shows the example which applied this invention to control of a brushless motor. It is a figure which shows the example of a general steering mechanism. It is a block diagram which shows the structural example of a conventional apparatus. It is a schematic diagram which shows the mode of the torque generate | occur | produced between a road surface and steering. It is a figure which shows the structural example of a SAT estimation feedback part. It is a figure which shows the example of a characteristic of a gain part. It is a block diagram which shows the structural example of a conventional apparatus. It is a block diagram which shows the structural example of a SAT feedback part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steering handle 3 Reduction gear 10 Torque sensor 12 Vehicle speed sensor 20 Motor 21 Motor drive part 100 Control unit 110 Torque system control part 111 Assist amount calculation part 112 Differential controller 113 Yaw rate convergence controller 114 Robust stabilization compensator 115 SAT Estimation feedback unit 117, 230 SAT estimation unit 118 Feedback unit 120 Motor system control unit 121 Compensator 122 Disturbance estimator 123 Motor angular velocity estimation unit 124 Motor angular acceleration estimation unit 125 Motor characteristic compensation unit 130, 250 SAT change rate feedback unit 131 Differentiation Calculation unit 132 Low-pass filter 133 Gain unit 200 Brushless motor 218 Angular velocity calculation unit 226 2-phase / 3-phase conversion unit

Claims (6)

A steering assist command value calculation unit that calculates a steering assist command value based on a torque signal from a torque sensor, a current control unit that calculates a voltage command value based on the steering assist command value, and a voltage control value based on the voltage command value A motor driving unit that drives a motor, and applies assist force by the motor to a steering system, and inputs angular velocity and angular acceleration of the motor, the steering assist command value, and the torque signal. In a control device for an electric power steering apparatus, provided with a SAT measurement unit for estimating SAT or measuring with a sensor, and feeding back the SAT value obtained by the SAT measurement unit to the steering assist command value, the change in the SAT value A SAT change rate feedback unit for calculating the rate is provided, and the SAT change rate obtained by the SAT change rate feedback unit is calculated in advance. Control device for an electric power steering apparatus characterized by being adapted to feedback to the steering assist command value. The control device for an electric power steering apparatus according to claim 1, wherein the SAT change rate feedback unit includes a differential calculation unit and a gain unit. The control device for an electric power steering apparatus according to claim 2, wherein the SAT change rate feedback unit further includes a low-pass filter. 4. The control device for an electric power steering apparatus according to claim 3, wherein a cut-off frequency of the low-pass filter and a gain of the gain unit can be changed according to a vehicle speed. The control device for the electric power steering apparatus according to claim 3 or 4, wherein a gain of the gain section can be changed by the torque signal. The control device for an electric power steering apparatus according to claim 3 or 4, wherein a gain of the gain section can be changed by a rotation speed of the motor.

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