JP3708228B2 - Electric power steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electric power steering device that directly reduces the steering force of a driver by directly applying the power of the motor to a steering system, and in particular, accurately transmits the road surface condition to the driver via a steering wheel, so that an optimum steering fee can be obtained. The present invention relates to an electric power steering apparatus capable of obtaining a ring.
[0002]
[Prior art]
In a conventional electric power steering apparatus, a steering torque generated by a driver operating a steering wheel is detected, and power generated by driving the motor by PWM (pulse width modulation) using a target current signal corresponding to the steering torque. Is configured to act on the steering system as an auxiliary steering force (assist force) to reduce the driver's steering force.
[0003]
In addition, by detecting the vehicle speed and controlling the target current signal to decrease as the vehicle speed increases, a sufficiently large assist force is applied to the steering system in the low vehicle speed range to reduce the steering force of the driver and In the vehicle speed range, there is also known one configured to stabilize the vehicle behavior by limiting the assist force to be small.
[0004]
FIG. 4 shows an overall configuration diagram of a conventional electric power steering apparatus.
In FIG. 4, a conventional electric power steering device 51 is provided in a steering gear box 54 via a connecting shaft 53 having a universal joint 53a, 53b on a steering shaft 52 provided integrally with a steering wheel 67. A manual steering force generating means 56 is configured by being connected to the pinion 55a of the rack and pinion mechanism 55.
[0005]
The rack shaft 57 provided with rack teeth 57a meshing with the pinion 55a and reciprocatingly engaged with the pinions 55a is connected to left and right front wheels 59 as rolling wheels via tie rods 58 at both ends thereof.
[0006]
In this way, during steering of the steering wheel 67, the front wheel 59 is rolled by manual steering through the normal rack and pinion type manual steering force generating means 56 to change the direction of the vehicle.
[0007]
In order to reduce the steering force generated by the manual steering force generating means 56, an electric motor 60 for supplying a steering assist force (assist force) is disposed coaxially with the rack shaft 57, and a ball screw mechanism provided coaxially with the rack shaft 57. The rotational force of the electric motor 60 is converted into a linear thrust through 61 and is applied to the rack shaft 57 (ball screw shaft 61a).
[0008]
A steering torque sensor 62 for detecting the direction and magnitude of the manual steering torque of the driver is arranged in the steering gear box 54, and a steering torque signal T _S of an analog electric signal corresponding to the steering torque detected by the steering torque sensor 62 is disposed. Is provided to the control means 65.
[0009]
The vehicle speed sensor 64 detects an electrical pulse signal having a frequency corresponding to the vehicle speed, and provides the vehicle speed signal V _S to the control means 65.
[0010]
The control means 65 is composed of various arithmetic means, processing means, signal generation means, memory, etc. based on a microprocessor, and a drive control signal V _O (for example, on-state) corresponding to the steering torque signal T _S responsive to the vehicle speed signal V _S. A mixed signal of the signal and the PWM signal) to drive and control the motor driving means 66.
[0011]
Motor drive means 66, for example constituted by a bridge circuit composed of switching elements of four power FET (field effect transistor), and generates a motor voltage V _M to drive the motor 60 based on the drive control signal V _O.
[0012]
The motor current detection means 68 detects the motor current I _M that actually flows through the motor 60 and feeds back (negative feedback) the motor current signal I _MO corresponding to the motor current I _M to the control means 65.
[0013]
FIG. 5 is an overall block diagram of a conventional electric power steering apparatus.
In FIG. 5, the electric power steering device 51 includes a steering torque sensor 62, a vehicle speed sensor 64, a control means 65, an electric motor drive means 66, an electric motor current detection means 68, and an electric motor 60.
[0014]
The control means 65 is composed of various arithmetic means, comparison / processing means, memory, etc. based on a microprocessor, and includes a target current setting means 71, a deviation arithmetic means 72, and a control signal generating means 73.
[0015]
The steering torque sensor 62 detects the steering torque corresponding to the steering operation of the driver (driver) as an analog electrical signal, the steering torque signal T _S is supplied to the target current setting means 71.
The vehicle speed sensor 64 detects an electrical pulse signal having a frequency corresponding to the vehicle speed, and the vehicle speed signal V _S is supplied to the target current setting means 71.
[0016]
Target current setting unit 71, a steering torque signal T _S fed into a steering torque signal T _D digital by the A / D converter or the like, from the steering torque signal T _D and the vehicle speed sensor 64 from the steering torque sensor 62 Based on the supplied vehicle speed signal V _S , the target current signal is converted into a preset target current signal I _MS and the target current signal for the steering torque signal T _D using the vehicle speed V _S (V _L , V _M , V _H ) as a parameter. It is configured to output the _IMS to the deviation calculating means 72.
[0017]
FIG. 6 shows a steering torque signal (T _D ) -target current signal (I _MS ) characteristic diagram with the vehicle speed as a parameter.
6, the vehicle speed V _L, V _M and V _H, respectively low vehicle speed region, represents the medium vehicle speed region and the high vehicle speed region, even in the steering torque signal T _D is the same, increases the vehicle speed V _S is (V _L → The target current signal _IMS is preset so as to decrease as V _M → V _H ).
[0018]
Thus, the target current setting means 71, the low vehicle speed range (V _S = V _L) in to the electric motor 60 is driven at the target current signal I _MS large motor corresponding to the current I _M sufficiently large steering assist force is obtained while limiting the steering assist force by driving a high vehicle speed range (V _S = V _H) in a small motor current and the motor 60 corresponding to the target current signal I _MS I _M, as the stability of steering can be obtained configuration Is done.
[0019]
The deviation calculating means 72 detects the deviation (= I _MS −I _MO ) of the motor current signal I _MO detected by the target current signal I _MS and the motor current detecting means 68 and converted into a digital signal corresponding to the motor current I _M. The deviation signal ΔI is calculated and provided to the control signal generating means 73.
[0020]
The control signal generating means 73 includes a PI controller and a PWM (pulse width modulation) signal generating means. The deviation signal ΔI is subjected to proportional / integral control, and then the PWM signal V _PWM corresponding to the magnitude and direction of the deviation signal ΔI. There is supplied to the motor driving unit 66 as a motor control signal V _O, the motor 60 is driven by the motor voltage V _M from the motor drive unit 66.
[0021]
In addition, the motor 60 is driven by the motor control signal V _O and the motor current I _M flows. The motor current detection unit 68 detects the motor current I _M , and the corresponding motor current signal I _MO is fed back to the deviation calculation unit 72. Is done.
[0022]
Thus, the conventional electric power steering apparatus 51, a target current signal I _MS to the motor current I _M motor current signal I _MO corresponding to fed back (negative feedback), so performing the proportional-integral control on a deviation signal ΔI Since the motor current signal _IMO is quickly converged to the target current signal _IMS , the motor power corresponding to the steering torque T _S is obtained, and the desired steering assist force with good response is applied to the steering system. Is possible.
[0023]
[Problems to be solved by the invention]
Conventional electric power steering apparatus sets a vehicle speed signal _{V S (= V L, V} M, V H) in accordance with the steering torque signal T _D which was the parameter target current signal I _MS as shown in FIG. 6 Thus, when the required manual steering force (steering torque signal T _S or T _D ) is reduced with respect to the required constant rack axial force _FLK , the same steering torque signal is used. It is necessary to increase the target current signal _IMS with respect to T _S (or T _D ).
[0024]
FIG. 7 shows a target current signal _IMS increase characteristic diagram with respect to the same steering torque signal T _S.
FIG. 7 shows a case where the C1 characteristic target current signal I _MS1 is increased from the C1 characteristic target current signal I _MS2 to the same steering torque signal T _S (= T _SK ).
[0025]
Shows the change illustration of the components of the corresponding rack shaft force F _L in FIG. 7 to FIG.
In FIG. 8, the rack axial force F _LK required corresponding to the C1 characteristic of FIG. 7 includes an assist force F _A1 component corresponding to the target current signal _IMS1 and a manual steering force (steering torque signal) T _S1 component. (The T _S1 component includes the road information I _L1 component from the road surface at a predetermined ratio.).
[0026]
If the same rack axial force _FLK is obtained even if the manual steering force is reduced from this state as shown in the C2 characteristic of FIG. 7, the rack axial force _FLK is an assist force corresponding to the target current signal _IMS2. The F _A2 component is combined with the manual steering force (steering torque signal) T _S2 component (the T _S2 component includes the road information I _L2 component from the road surface at a predetermined ratio) (F _LK = F _A2 + T _S2 ).
[0027]
The rack axial force _FLK is the same, and the ratio of the load information I _L2 component (= I _L2 / T _S2 ) included in the manual steering force (steering torque signal) T _S2 component is the manual steering force (steering torque signal) T _Since the ratio of the load information I _L1 component contained in the _S1 component (= I _L1 / T _S1 ) is the same, the load information I _L2 component is the ratio of the assist force F _A1 component and the assist force F _A2 component (= F _A1 / F _A2 ) will be reduced.
[0028]
The reduction of the manual steering force (steering torque signal) _TS1 component to the manual steering force (steering torque signal) _TS2 component satisfies the original required specifications of the electric power steering device by increasing the assist force. The reduction from the I _L1 component to the road information I _L2 component is a factor that prevents the driver from accurately recognizing the road surface condition through the steering wheel and performing optimum steering operation. This is a major problem for electric power steering devices.
[0029]
Road information refers to road surface information (for example, a steering wheel) transmitted from a rack shaft to a driver through a steering wheel when traveling on a rough road surface or a low μ road surface (a road surface having a small friction coefficient) such as a frozen road. Vibration, a phenomenon that the handle operation suddenly becomes lighter).
[0030]
The present invention has been made to solve such problems, and its purpose is to directly apply the power of the motor to the steering system to assist the manual steering force, and to accurately provide road information to the driver via the steering wheel. An object of the present invention is to provide an electric power steering apparatus that can obtain an optimum steering feeling corresponding to a road surface condition by transmitting.
[0031]
[Means for Solving the Problems]
In order to solve the above-described problems, an electric power steering apparatus according to the present invention forms a generalized plant for modeling a desired control target by incorporating a control specification desired to be realized in the control target of the steering system and an input of the generalized plant Weighting function generating means for performing different weights in different systems between the rack shaft input or steering wheel input and the reaction force torque output forming the output, and the target current input of the generalized plant from the reaction force torque output And a control means for setting a target current signal for driving the electric motor in the feedback loop.
[0032]
An electric power steering apparatus according to the present invention includes a generalized plant for modeling a desired control target by incorporating a control specification desired to be realized in a control target of a steering system, and a rack shaft input or handle for forming an input of the generalized plant In the feedback loop from the reaction force torque output to the target current input of the generalized plant, there is provided a weighting function generating means for performing independent weighting in a separate system between the input and the reaction force torque output forming the output. The control means for setting the target current signal to drive the motor is equipped with, so that the road surface information (road information) from the rack shaft input can be accurately transmitted to the driver and the accuracy corresponding to the handle input It is possible to generate a good assist force.
[0033]
Further, the weighting function generating means of the electric power steering apparatus according to the present invention has a weighting relating to the frequency, and has a band elimination filter characteristic for the rack shaft input and a low pass filter characteristic for the handle input. It is characterized by that.
[0034]
The electric power steering apparatus according to the present invention has a weighting function generating means having a weight related to the frequency, a band elimination filter characteristic for the rack shaft input, and a low-pass filter characteristic for the handle input. Therefore, both relatively high-frequency road surface information (road information) required by the driver and low-frequency steering assist force can be controlled independently.
[0035]
Furthermore, the control means of the electric power steering apparatus according to the present invention is characterized by being obtained by the H infinity (H∞) method.
[0036]
Since the electric power steering apparatus according to the present invention applies the H infinity (H∞) method to the generalized plant and the control means and determines the control means, an optimal control system can be realized.
[0037]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings.
In addition, the present invention introduces a generalized plant that incorporates a control specification to be realized in a steering system to be controlled and models a desired control target, and performs control by applying an H infinity (H∞) method thereto. By determining the means, stable steering control is performed.
[0038]
In addition, the present invention provides a generalized plant with independent frequency characteristic weighting functions for the steering wheel input and the rack shaft input, respectively, to supply the steering system with an optimal assist force, and to provide the road surface necessary for the driver. An electric power steering device that accurately conveys information (road information) is provided.
[0039]
FIG. 1 is a basic block diagram of an electric power steering apparatus according to the present invention.
In FIG. 1, an electric power steering apparatus 1 includes a generalized plant 2 for modeling a desired control target by incorporating a control specification to be realized in a control target of a steering system, a reaction force torque output of the generalized plant 2 and a target. Control means 7 is connected to a feedback loop between the current inputs and sets a target current signal for driving the electric motor.
[0040]
Here, the control specifications to be realized assume road information (road surface information) on a low μ road having a low road surface frictional resistance such as a frozen road transmitted from a rack shaft, steering information from a steering wheel, and the like.
[0041]
In a vehicle with only manual steering (manual steering), road information on a low μ road is accurately transmitted to the driver via the steering wheel.
[0042]
Road information (road surface information) for low μ roads is included in the rack axial force from the rack axis, and tends to appear prominently in a specific frequency band higher than the frequency band required for steering. The road surface information of the band is passed through the handle.
[0043]
On the other hand, steering information from the steering wheel tends to concentrate on a relatively low frequency band from direct current (DC), and can be handled clearly separated from the frequency band of road information (road surface information) on low μ roads. .
[0044]
Paying attention to the frequency band difference between road information (road surface information) and steering information (handle torque) from the steering wheel, the required specifications for road information and steering information requested by the driver are set as follows: Then, it is taken into the generalized plant 2 shown in FIG.
In addition, a required specification is set for noise mixed in the torque sensor.
[0045]
Required specifications:
(1) The transfer characteristic from rack axial force (rack shaft input) to reaction torque (reaction torque output) is controlled by assist control in a relatively low frequency band from the direct current (DC) component, and a relatively high specific frequency. Assist control is not performed in the band.
{Circle around (2)} The transfer characteristic from the handle torque (handle input) to the reaction force torque (reaction force torque output) performs assist control in a relatively low frequency band from the direct current (DC) component.
(3) Robust (robust) against noise mixed in the torque sensor.
[0046]
In FIG. 1, a generalized plant 2 that incorporates the required specifications (1) to (3) is a power steering model 3 in which electrical and mechanical modeling of a conventional electric power steering device is performed. request to the rack shaft force F _R specifications ▲ 1 ▼ a for realizing rack shaft input weighting function 4, handle input weighting function 5 for realizing the required specifications ▲ 2 ▼ to handle torque F _H from the steering wheel input, noise input And a torque output weighting function 6 for realizing the required specification (3) in the noise N _O mixed in the torque sensor.
The rack shaft input weighting function 4, the handle input weighting function 5, and the torque output weighting function 6 form weighting function generating means.
[0047]
The control means 7 has a transfer function that does not include an integral element, and controls the generalized plant 2 based on the rack axial force F _R supplied from the rack shaft input of the generalized plant 2 and the handle torque F _H from the handle input. The reaction force torque T _R obtained by solving as an H infinity (H∞) standard problem and output from the reaction force torque output is set to the target value 0, and thus is handled as regulator control with the target value 0.
[0048]
FIG. 2 is a control block diagram of a system including the generalized plant shown in FIG.
In FIG. 2, P _E (12) represents the electrical characteristics of the motor (1 / (L * s + R)), K _T (13) and K _E (16) represent the torque constant and back electromotive voltage constant of the motor, respectively. P _M (15) is the mechanical characteristics of the motor (1 / (J _M * s ² + B * s)), a (17) is the gear ratio, K (19) is the stiffness coefficient of the torsion bar, and P _H (23) Represents the mechanical properties of the handle.
[0049]
Further, KI (20) represents a control unit which does not include the integral element by converting a reaction torque T _R to the target current signal I _MS, H infinity (H∞) Method (control), a handle torque F _H The reaction torque T _R is controlled to 0 so that the rack axial force F _R becomes equal.
[0050]
W1 (21) represents the rack shaft input weighting function were weighted with a band elimination filter characteristics with a relatively high specific frequency band to the rack shaft force F _R including road information supplied from the rack shaft Input Thereafter, it is supplied to the minus input of the subtracting means 14.
[0051]
W2 (22) represents a handle input weighting function. The handle torque F _H supplied from the handle input is weighted from a direct current (DC) component having a low-pass filter characteristic in a relatively low frequency band, and then P _H ( 23) to the adding means 18 via.
[0052]
Thus, supplies the output of the W1 (21) to the subtracting unit 14, by supplying the output of the W2 (22) to the adding means 18 through the P _H (23), the rack shaft force F _R and the handle The torque F _H is input to a separate system between the rack shaft input and the reaction force torque output and between the handle input and the reaction force torque output.
[0053]
FIG. 3 is a frequency characteristic diagram of the weighting function according to the present invention.
In FIG. 3, W1 represents a weighting coefficient of the rack axis input weighting function, W2 represents a weighting coefficient of the handle input weighting function, and W3 represents a weighting coefficient of the torque output weighting function.
[0054]
The weighting factors W1, W2, and W3 may be considered as assist forces (gains) in the control block diagram of the system shown in FIG.
[0055]
The weighting coefficient W1 has a constant assist force (gain) from a direct current (DC) to a relatively low frequency, and has a band elimination filter characteristic in a specific frequency band F _B of the frequencies f _{O1 to} f _O3 . setting the frequency characteristic to pass without attenuation the road information from the low μ road contained in the rack shaft force F _R which is supplied from the rack shaft input.
[0056]
The weighting coefficient W2 has a low-pass filter characteristic that provides a constant assist force (gain) in the steering region from direct current (DC) to the vicinity of the frequency f _O3, and corresponds to the handle torque F _H supplied from the handle input. The characteristics are set so that torque (F _HW shown in FIG. 1) can be obtained.
[0057]
The weighting coefficient W3 has a characteristic of increasing the torque output _TK as the frequency f increases, and sets the characteristic so as to obtain robustness against noise mixed in the torque sensor.
[0058]
As described above, the weighting coefficient W1 for passing the road information and the weighting coefficient W2 for generating the assist force corresponding to the steering torque can be set independently.
[0059]
【The invention's effect】
As described above, the electric power steering apparatus according to the present invention forms a generalized plant for modeling a desired control target by incorporating a control specification desired to be realized in the control target of the steering system and an input of the generalized plant. Weighting function generating means for performing independent weighting in a separate system between the rack shaft input or steering wheel input and the reaction force torque output forming the output, and from the reaction force torque output, the target current of the generalized plant Control means to set the target current signal for driving the motor in the feedback loop to the input, it is possible to accurately transmit road surface information (road information) from the rack shaft input to the driver and handle input It is possible to generate a precise assist force corresponding to the Thereby assisting the steering force, it is possible to realize a steering corresponding to road information transmitted through the handle.
[0060]
The electric power steering device according to the present invention has a weighting function with respect to frequency, and has a band elimination filter characteristic for a rack shaft input and a low pass filter characteristic for a handle input. And can control both the relatively high-frequency road surface information (road information) required by the driver and the low-frequency steering assist force independently, so that the manual steering force can be optimally assisted. , Optimal steering operation corresponding to road information can be performed.
[0061]
Furthermore, the electric power steering apparatus according to the present invention can perform an H infinity (H∞) method on the generalized plant and the control means, determine the control means, and realize an optimal control system. Highly accurate and stable power assist can be realized.
[0062]
Therefore, it is possible to provide an electric power steering device that realizes high-accuracy and stable power assist and has a good steering feeling that enables appropriate steering for road information.
[Brief description of the drawings]
FIG. 1 is a basic block diagram of an electric power steering device according to the present invention. FIG. 2 is a control block diagram of a system including a generalized plant shown in FIG. 1. FIG. 3 is a frequency characteristic diagram of a weighting function according to the present invention. FIG. 4 is an overall block diagram of a conventional electric power steering device. FIG. 5 is an overall block diagram of a conventional electric power steering device. FIG. 6 is a steering torque signal (T _D ) —target current signal (I) with vehicle speed as a parameter. _MS) characteristic diagram [7] a target current signal I _MS increasing characteristic relative to the same steering torque signal T _S diagram 8 change illustration of the components of the rack shaft force F _L which corresponds to FIG. 7 [description of symbols]
DESCRIPTION OF SYMBOLS 1 ... Electric power steering apparatus, 2 ... Generalized plant, 3 ... Power steering model, 4 ... Rack axis input weighting function, 5 ... Handle input weighting function, 6 ... Torque output weighting function, 7 ... Control means, 11, 14 ... Subtracting means 12 ... P _E (motive electrical characteristics), 13 ... K _T (motor torque constant), 15 ... P _M (motor mechanical characteristics), 16 ... K _E (back electromotive voltage constant), 17 ... a (gear ratio), 18 ... adding means, 19 ... K (stiffness coefficient of torsion bar), 20 ... KI (control means), 21 ... W1 (rack axis input weighting function), 22 ... W2 (handle input weighting function) ), 23... P _H (mechanical characteristics of the handle), F _R ... Rack axial force, F _H ... Handle torque, T _R .. reaction torque, I _MS .

Claims (3)

Electric power that includes a steering torque detecting means for detecting the steering torque of the steering system and an electric motor, controls the power of the electric motor using the control means, and acts on the steering system to reduce the steering force of the driver In the steering device,
A generalized plant for modeling a desired control object by incorporating a control specification to be realized in the control object of the steering system;
A weighting function generating means for performing independent weighting in a separate system between the rack shaft input or handle input forming the input of the generalized plant and the reaction force torque output forming the output, respectively,
An electric power steering apparatus comprising control means for setting a target current signal for driving the electric motor in a feedback loop from the reaction force torque output to a target current input of the generalized plant. 2. The weighting function generating means has frequency weighting, and has a band elimination filter characteristic for a rack axis input and a low pass filter characteristic for a handle input. Electric power steering device. 2. The electric power steering apparatus according to claim 1, wherein the control means is obtained by an H infinity (H∞) method.

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