JP5034725B2 - Control device for electric power steering device - Google Patents

Description

  The present invention corrects the current command value (or steering assist command value) with the estimated value of the self-aligning torque (SAT), and drives the motor with the corrected current command value to control the steering assist force in the vehicle steering system. In particular, it is possible to improve the steering feeling of the driver by correcting the neutral point of the SAT based on the wheel speed difference without using the rudder angle sensor. The present invention relates to a control device for an electric power steering device.

  An electric power steering device for energizing a vehicle steering device with an auxiliary load by a rotational force of a motor energizes an auxiliary load to a steering shaft or a rack shaft by a transmission mechanism such as a gear or a belt via a speed reducer. It is supposed to be. 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. 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. A power is supplied from the battery 14 to the control unit 30 that controls the power steering device, and an ignition signal is input through the ignition key 11. The control unit 30 detects the steering torque Th detected by the torque sensor 10 and the vehicle speed. An assist command steering assist command value I is calculated based on the vehicle speed V detected by the 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 MPU and MCU), and FIG. 10 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. 10. The steering torque Th detected by the torque sensor 10 is input to the steering assist command value calculation unit 32, and the vehicle speed V detected by the vehicle speed sensor 12 is also steered. This is input to the auxiliary command value calculation unit 32. The steering assist command value calculation unit 32 refers to the assist map stored in the memory 33 based on the input steering torque Th and the vehicle speed V, and the steering assist command is a control target value of the current supplied to the motor 20. Determine the value I. The steering assist command value I is input to the subtraction unit 30A and is also input to the feedforward differential compensation unit 34 for increasing the response speed, and the deviation (Ii) of the subtraction unit 30A is input to the proportional calculation unit 35. At the same time, it is input to the integral calculation unit 36 for improving the characteristics of the feedback system, and its proportional output is input to the addition unit 30B. The outputs of the differential compensator 34 and the integral compensator 36 are also added to the adder 30B, and the current control value E, which is the addition result of the adder 30B, is input to the motor drive circuit 37 as a motor drive signal. Electric power is supplied from the battery 14 to the motor drive circuit 37, the motor current value i of the motor 20 is detected by the motor current detector 38, and the motor current value i is input to the subtractor 30A and fed back.

  In such an electric power steering apparatus, so-called steering wheel return control is performed. That is, in the vehicle steering device, the driver releases his / her steering force from the steering wheel cut to one side, and the steering force is released, so that the steered wheels are naturally returned to the neutral position. However, in an ordinary electric power steering apparatus, if the steering wheel is expected to return to the neutral position naturally, the steering wheel is difficult to return particularly at low speeds. This is because, when the steering wheel naturally returns from the road surface due to the force applied to each steered wheel, there is an influence such as an inertia moment and a frictional resistance that the motor and the speed reducer have. As a result, even if the driver removes his / her hand from the handle, the return of the handle is slow, or the handle does not return to the neutral position, so the driver must not actively return the handle to the neutral position. The workload is large.

  In order to eliminate such inconvenience, Japanese Patent Laid-Open No. 3-11944 (Patent Document 1) discloses that when the torque for turning the steering wheel in one direction is weakened, the return steering is automatically performed and the steering wheel is neutral. An electric power steering device that returns to position is disclosed. According to the electric power steering device disclosed in Patent Document 1, it is not necessary to perform a positive driving operation for returning the steering wheel to the neutral position, and the workload of the driver is reduced.

However, in the electric power steering device disclosed in Patent Document 1, in addition to the hardware configuration of a normal electric power steering device, a steering angle sensor for detecting the steering angle of the steering wheel with respect to the steered wheels is necessary. The cost increase is inevitable, and there is a problem that the manufacturing cost increases.
As an apparatus for solving this problem, an electric power steering apparatus disclosed in Japanese Patent Laid-Open No. 2000-238652 (Patent Document 2) has been proposed. The electric power steering device disclosed in Patent Document 2 detects a steering torque applied to a steering column and a pair of left and right wheel speed sensors that respectively generate wheel speed signals relating to the rotational angle positions or rotational angular speeds of the left and right wheels. An electric power steering apparatus comprising: a torque sensor that generates a steering torque signal; a motor that reinforces the steering torque to increase the steering force; and a control unit that drives the motor based on at least one of the wheel speed signals and the steering torque signal. The control unit generates a wheel speed difference signal indicating a speed difference between the left and right wheels based on the wheel speed signal, and motor terminal voltage and motor current detection values applied to the motor. Motor rotational angular velocity estimating means for estimating the motor rotational angular velocity based on the steering torque signal, wheel speed difference signal And a steering wheel return detecting means for determining whether or not the steering wheel is in a returning state based on the motor rotational angular velocity, and a steering wheel that is appropriate for the motor when the steering wheel return detecting means determines that the steering wheel is in the returning state. And a return correction control means for generating a return correction signal.
JP-A-3-11944 Japanese Patent Laid-Open No. 2000-238652

  However, the electric power steering device of Patent Document 2 does not correspond to the situation where the steering wheel is desired to be returned, and is not sufficient as steering wheel return control, and there is a problem that the driver feels that the steering wheel is returned.

  The present invention has been made under the circumstances as described above, and an object of the present invention is to reduce the current command value (or the SAT estimated value) without using the steering angle sensor and without deteriorating the steering feeling. Provided is a control device for an electric power steering device that can further improve the driver's steering feeling by correcting the steering assist command value) and correcting the neutral point of the SAT estimated value based on the wheel speed signal. There is to do.

The present invention relates to a control device for an electric power steering apparatus that drives and controls a motor that applies assist torque to a steering system based on a current command value calculated based on the steering torque and the vehicle speed, and the object of the present invention is to estimate SAT. SAT estimating means for correcting the current command value based on the estimated SAT value estimated by the SAT estimating means, and offset amount calculating means for calculating the offset amount based on the wheel speed signal. The offset amount calculation means calculates a wheel speed difference calculation unit that calculates a wheel speed difference based on the wheel speed signal, a steering angle estimation unit that estimates a steering angle based on the wheel speed difference, and the steering angle estimation And an offset amount calculation unit that calculates the offset amount based on the estimated steering angle estimated by the unit, and the off amount calculated by the offset amount calculation unit It is achieved by correcting the neutral point of the SAT estimated value by adding the Tsu bets amount to the SAT estimated value.
The present invention also relates to a control device for an electric power steering device that drives and controls a motor that applies assist torque to the steering system based on a current command value calculated based on the steering torque and the vehicle speed. SAT estimating means for estimating; correcting means for correcting the current command value based on the SAT estimated value estimated by the SAT estimating means; and offset amount calculating means for calculating the offset amount based on the wheel speed signal. The offset amount calculating means calculates a wheel speed difference calculation unit that calculates a wheel speed difference based on the wheel speed signal, a steering angle estimation unit that estimates a steering angle based on the wheel speed difference, and the steering angle A first function converter that outputs a SAT nominal value based on the estimated steering angle estimated by the estimator; a second function converter that performs gain conversion in response to the vehicle speed; and the SA A multiplier that multiplies the nominal value and the output of the second function converter, a filter that removes noise from the output of the multiplier, and a gain that uses the output of the filter as the offset amount with a gain corresponding to the current command value And is achieved by correcting the neutral point of the SAT estimated value by adding the offset amount from the gain unit to the SAT estimated value .

  According to the control device for the electric power steering apparatus of the present invention, the current command value (or steering assist command value) is corrected by the SAT estimated value without using the steering angle sensor, and the wheel speed difference based on the wheel speed signal is corrected. Thus, the steering angle is estimated and the neutral point of the SAT estimated value is corrected based on the estimated steering angle value. Therefore, the steering feeling can be improved with an inexpensive configuration.

  Further, since the current command value (or steering assist command value) is corrected by correcting the SAT estimated value, the steering wheel return control can be executed according to the situation where the steering wheel is to be returned.

  The control device of the electric power steering apparatus according to the present invention uses a current command value based on a SAT estimated value estimated based on a steering torque, an angular velocity, an angular acceleration, and a current command value (steering assist command value) without using a steering angle sensor. (Or steering assist command value) is corrected, the wheel speed difference is calculated based on the wheel speed signal, the steering angle is estimated based on the wheel speed difference, and the offset amount is calculated based on the steering angle estimated value. The neutral point (dead zone) of the SAT estimated value is corrected by the calculated offset amount. For this reason, steering wheel return control can be executed according to the situation where the steering wheel is to be returned, and since it is not necessary to provide a steering angle sensor, it is inexpensive and the neutral point of the SAT estimated value is corrected. The steering feeling of the person can be improved.

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

  In the present invention, since the current command value (steering assist command value) is corrected based on the estimated SAT value, the generation principle of SAT will be described first.

SAT is a force for returning the steering wheel to the original position, and as shown in FIG. 1, a steering torque Th is generated when the driver steers the steering wheel, and the motor M reduces the assist torque Tm according to the steering torque Th. appear. As a result, the front wheels are steered and SAT is generated as a reaction force. At that time, the torque that becomes the steering steering resistance is generated by the equivalent inertia J and the friction torque Fr that combine the inertia of the motor M and the inertia of the steering mechanism, and considering the balance of these forces, Is obtained. Note that ω is an angular velocity and ω ^* is an angular acceleration.

次に、本発明の前提となる基本制御系を図２に示して説明する。図２の構成は、上記数１に基づいて構成されたものである。

Next, a basic control system as a premise of the present invention will be described with reference to FIG. The configuration of FIG. 2 is configured based on Equation 1 above.

The steering torque Th detected by the torque sensor is input to the assist map 59A, the differentiator 51 and the adding unit 45B in the SAT estimation means 40, and the basic assist torque Tha calculated in the assist map 59A is the transfer function “(T ₁ S + 1) / (T ₂ · s + 1) "is transferred to the adder / subtractor 50A as the basic assist torque Thb (corresponding to the current command value or the steering assist command value) through the transfer function unit 59B. Further, the steering torque differentiated in the differentiator 51 for differential compensation is multiplied by the gain Kd in the gain unit 52, and the compensated differential compensation torque Thc is added to the addition / subtraction unit 50A. The SAT estimated value SAT ^* estimated by the SAT estimating means 40 is gain-calculated by the gain unit 43, the SAT feedback compensation value SAT ^* f from the gain unit 43 is subtracted and input to the adder / subtractor 50A, and added / subtracted by the adder / subtractor 50A. The processed current command value I is input to the transfer function unit 53 and the transfer function unit 44. Each of the transfer function units 53 and 44 has a transfer function Kt · G (Kt is a motor torque constant, G is a reduction gear ratio), and the transfer function unit 53 is an assist torque actually generated by the motor and the reduction gear. The transfer function unit 44 is a block indicating that conversion is performed using estimated logic (software).
The assist torque TA multiplied by the transfer function Kt · G in the transfer function unit 53 is input to the subtracting unit 50B in the block A, and the assist (assist) by the motor multiplied by the transfer function Kt · G in the transfer function unit 44 is performed. ) Torque Tm (= I · Kt · G) is input to the adder 45B, and the torque signal “Th + Tm” added to the steering torque Th by the adder 45B is input to the subtractor 45C.

Block A is a transfer function block in which the mechanism is simply modeled, J is inertia (= equivalent inertia combining motor inertia and inertia of the steering mechanism), and Fr is friction torque. Further, the actual SAT from the vehicle is subtracted and input to the subtracting unit 50B in the block A, and the angular velocity (column shaft angular velocity) ω _A from the block 58 is subtracted by the Fr · sign (ω _A ) via the friction calculating unit 54. The acceleration torque TC, which is the result of the subtraction processing by the subtraction unit 50B, is fed back to the block 58. The angular velocity ω _A from the block 58 is integrated by the integrator 57 to become an angle θ. The angle θ is input to an angle detection unit such as a resolver (not shown), the detected angle θ is input to the angular velocity calculation unit 56, and the angular velocity ω calculated by the angular velocity calculation unit 56 is the angular acceleration calculation unit 55 and the SAT estimation unit 40. The angular acceleration ω ^* is calculated by the angular acceleration calculating unit 55. The angular acceleration ω ^* is input to the inertia calculation unit 47 in the SAT estimation unit 40.

Incidentally, the block 57 is intended to indicate a transfer function of an angle theta from the column shaft angular velocity omega _A, rather than measuring the column shaft angular velocity omega _A direct angle of the motor obtained through a reduction gear of the speed reduction ratio G theta Is obtained to obtain the angular velocity ω and the motor angular velocity / reduction ratio is obtained, which becomes the column shaft angular velocity, but substantially ω _A = ω.
On the other hand, the angular velocity ω calculated by the angular velocity calculating unit 56 is input to the adding unit 45A as Fr · sign (ω) via the friction calculating unit 41 in the SAT estimating means 40, and the angular acceleration from the angular acceleration calculating unit 55 is input. ω ^* is input to the inertia calculation unit 47, J · ω ^*, which is the output of the inertia calculation unit 47, is input to the addition unit 45A, and the calculation value h (= J · ω ^* + Fr · sign (ω)) is subtracted and input to the subtracting unit 45C. In the subtraction unit 45C, the calculation value h is subtracted from the torque signal “Th + Tm”, and the subtraction result is input to the Q filter 42 for feeding back only information necessary and sufficient to improve the driver's steering feeling. The SAT estimated value SAT ^* , which is the output of the Q filter 42, is input to the gain unit 43 having the SAT gain Ks set so that the driver has a steering torque that matches the behavior of the vehicle. SAT feedback compensation value SAT ^* f is subtracted and input to the adder / subtractor 50A.
The SAT estimation means 40 includes a friction calculation unit 41, a Q filter 42, a transfer function unit 44, an inertia calculation unit 47, and the like.

In the basic control system of FIG. 2 as the premise of the present invention, the SAT feedback compensation value SAT ^* f calculated by the SAT estimation means 40 and the gain unit 43 is input to the addition / subtraction unit 50A, and the basic steering torque Thb and the differential The current command value I, that is, the assist torque TA is corrected by subtracting from the added value of the compensation torque Thc.

Here, the relationship between the SAT estimated value SAT ^* estimated by the SAT estimating means 40 and the actual SAT actually measured by the sensor is as shown in FIG. 3, and a dead zone occurs in the SAT estimated value SAT ^* . That is, in a motor with a brush, the angular velocity ω is generally estimated from the motor terminal voltage and the motor current value. However, since there is a dead band process for removing noise, the angular velocity ω with high accuracy cannot be obtained. Since the SAT cannot be accurately estimated when the angular velocity ω is zero, the actual SAT and the estimated SAT value SAT ^* have a dead zone characteristic as shown in FIG. Therefore, in the present invention, when the SAT estimated value SAT ^* is zero, the steering angle estimated value θ ^* (= SAT ^* (θ ^* )) obtained from the wheel speed difference is corrected (offset) as X1 and X2 in FIG. ) And handle return control is executed so that SAT = 0.
Since the wheel speed signal already exists in a vehicle having an anti-lock brake system (ABS), it can be used as it is, and the wheel speed difference Wd can be calculated from the wheel speed signal. Then, the steering angle estimated value θ ^* obtained by estimating the steering angle θ based on the wheel speed difference Wd can be obtained, the offset amount OFS is calculated from the steering angle estimated value θ ^* , and the SAT estimated value SAT ^* is calculated from the offset amount OFS ^. Correct (offset) the neutral point. Thus, since the neutral point of the SAT estimated value SAT ^* is corrected by the offset amount OFS, it is possible to perform the return control to the steering wheel neutral position using the front wheel left and right wheel speed signals without using the steering angle sensor.

  Based on the principle described above, an example of the embodiment of the present invention will be described with reference to FIG. FIG. 4 corresponds to the basic control system shown in FIG. 2, and the same members are denoted by the same reference numerals and description thereof is omitted.

In the present invention, as the offset amount calculating means, based on the wheel speed difference calculating unit 60 that calculates the wheel speed difference Wd based on the wheel speed signals of the left and right front wheels, and the wheel speed difference Wd calculated by the wheel speed difference calculating unit 60. A steering angle estimation unit 61 that estimates the steering angle (steering angle estimation value = θ ^* ), and an offset amount calculation unit that calculates the offset amount OFS based on the steering angle estimation value θ ^* estimated by the steering angle estimation unit 61 62. Then, the offset amount OFS calculated by the offset amount calculation unit 62 is input to the addition unit 63, added with the SAT feedback compensation value SAT ^* f from the gain unit 43, and corrected, and the addition result (= OFS + SAT ^* f) is obtained. The current command value (steering assist command value) I is corrected by subtracting the SAT feedback compensation value SAT ^* c into the adder / subtractor 50A.

  The wheel speed difference calculation unit 60 performs calculation based on the pair of left and right wheel speed signals by, for example, counting the interval between the pulse signals from the pair of left and right wheel speed sensors with a pulse counter, and A wheel speed difference Wd indicating a speed difference is generated. That is, since the difference in rotational speed between the left and right wheels occurs while the vehicle is turning to the left or right, the wheel speed difference calculation unit 60 detects the difference and performs a numerical calculation to thereby determine the speed of the left and right wheels. A wheel speed difference Wd indicating the difference is generated.

A method in which the rudder angle estimation unit 61 obtains the rudder angle estimated value θ ^* based on the wheel speed difference Wd will be described with reference to FIGS. 5 and 6. 4-wheel fl as shown in FIG. 5, fr, rl, each turning radius of rr and Rfl, Rfr, Rrl, and Rrr, and the front wheels fl, the steering angle of the fr convenience alpha _l, and alpha _r, an axle of the vehicle The distance is L, and the vehicle width (the distance between the centers of the left and right wheels) is E. The turning radius at the center of the front wheel axle is Rf, and the turning radius at the center of the rear wheel axle is Rr. As the wheel speeds (wheel angular velocities) of the wheels fl, fr, rl, rr, the left front wheel is ω _fl , the right front wheel is ω _fr , the left rear wheel is ω _rl , and the right rear wheel is ω _rr . It is known that the steering angle α (see FIG. 6) and the wheel speeds ω _fl , ω _fr , ω _rl , and ω _rr have the relationship of the following formula 2.

上記数２の舵角α_{ｆｒｏｎｔ}は、舵角推定値θ^＊に相当している。

The steering angle α _{front in Equation} 2 corresponds to the estimated steering angle θ ^* .

The calculation by the rudder angle estimation unit 61 may be calculated by the above formula 2, or may be configured by a look-up table that inputs (ω _fl −ω _fr ) / (ω _fl + ω _fr ).

Next, the offset amount calculation unit 62 will be described. The offset amount calculation unit 62 may multiply the steering angle estimation value θ ^* from the steering angle estimation unit 61 by a predetermined value to obtain the offset amount OFS. The predetermined value may be variable according to the vehicle speed V, and the output may be limited by providing a limiter for the final calculated value. Further, as in Japanese Patent Application No. 2006-129331, in the configuration of FIG. 7, the standard SAT may be obtained from the steering angle estimated value θ ^* and the vehicle speed V, and the offset amount OFS may be obtained according to the standard SAT. In this case, the current command value corresponding to the normative SAT is given as the offset amount OFS in the vicinity of the SAT estimated value SAT ^* being zero.

Further, as shown in FIG. 8, the offset amount OFS may be obtained based on the estimated steering angle value θ ^* and the vehicle speed V. That is, the steering angle estimated value θ ^* is input to the multiplication unit 66 as the SAT nominal value Nv in the function conversion unit 64, and the vehicle speed V is input to the multiplication unit 66 through the function conversion unit 65 of the vehicle speed sensitive gain. The offset amount OFS is obtained by passing the multiplication result of 66 through the noise removal filter 67 and the gain unit 68 of the conversion coefficient Kn. Note that the conversion coefficient Kn of the gain unit 68 is a coefficient for making the current command value equivalent.

It is a schematic diagram which shows the mode of the torque generate | occur | produced from a road surface to a steering. It is a block diagram which shows the basic control system used as the premise of this invention. It is a characteristic view which shows the relationship between real SAT and a SAT estimated value. It is a block diagram which shows an example of embodiment of this invention. It is a schematic diagram for demonstrating a wheel speed difference. It is a schematic diagram for demonstrating a wheel speed difference. It is a block diagram for demonstrating an example of normative SAT calculation. It is a block diagram for demonstrating an example of offset amount calculation. It is a figure which shows the structural example of the conventional steering device. It is a block diagram which shows the structural example of the control unit of the conventional steering apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Handle 2 Column shaft 10 Torque sensor 12 Vehicle speed sensor 20 Motor 30 Control unit 32 Steering assistance command value calculating part 40 SAT estimation means 41, 54 Friction calculating part 42 Q filter 43, 52 Gain part 44, 53, 59B Transfer function part 55 Angular acceleration calculator 56 Angular velocity calculator 59A Assist map 60 Wheel speed difference calculator 61 Steering angle estimator 62 Offset amount calculator 64, 65 Function converter 66 Multiplier 67 Filter

Claims (2)

In a control device for an electric power steering device that drives and controls a motor that applies assist torque to a steering system based on a current command value calculated based on steering torque and vehicle speed,
SAT estimating means for estimating SAT, correcting means for correcting the current command value based on the SAT estimated value estimated by the SAT estimating means, offset amount calculating means for calculating an offset amount based on a wheel speed signal, Comprising
The offset amount calculation means calculates a wheel speed difference calculation unit that calculates a wheel speed difference based on the wheel speed signal, a steering angle estimation unit that estimates a steering angle based on the wheel speed difference, and the steering angle estimation unit And an offset amount calculation unit that calculates the offset amount based on the estimated steering angle estimated at
A control device for an electric power steering apparatus, wherein a neutral point of the SAT estimated value is corrected by adding the offset amount calculated by the offset amount calculating unit to the SAT estimated value . In a control device for an electric power steering device that drives and controls a motor that applies assist torque to a steering system based on a current command value calculated based on steering torque and vehicle speed,
SAT estimating means for estimating SAT, correcting means for correcting the current command value based on the SAT estimated value estimated by the SAT estimating means, offset amount calculating means for calculating an offset amount based on a wheel speed signal, Comprising
The offset amount calculation means calculates a wheel speed difference calculation unit that calculates a wheel speed difference based on the wheel speed signal, a steering angle estimation unit that estimates a steering angle based on the wheel speed difference, and the steering angle estimation unit A first function conversion unit that outputs a SAT nominal value based on the estimated steering angle estimated in step S2, a second function conversion unit that performs gain conversion in response to the vehicle speed, the SAT nominal value, and the second function conversion. A multiplication unit that multiplies the output of the unit, a filter that removes noise from the output of the multiplication unit, and a gain unit that uses the output of the filter as the offset amount with a gain corresponding to the current command value,
A control device for an electric power steering apparatus, wherein a neutral point of the SAT estimated value is corrected by adding the offset amount from the gain unit to the SAT estimated value .

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