JP4453012B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an electric power steering device that assists steering by driving an electric motor in accordance with an operation of an operation member such as a steering wheel and transmitting the power of the electric motor to a steering mechanism.

2. Description of the Related Art Conventionally, an electric power steering configured to transmit the power of an electric motor to a steering mechanism is mounted on a vehicle and used. The electric motor is driven and controlled in accordance with the operation torque applied to the steering wheel and the vehicle speed. More specifically, the target current value corresponding to the operation torque and the vehicle speed is determined in advance, and the electric motor is set so that the actual motor current becomes the target current value corresponding to the detected value of the operation torque and the vehicle speed. Feedback controlled.
JP 2004-74833 A JP 2004-90834 A JP 2004-131046 A

However, in the conventional electric power steering device, the relationship between the operating torque and the steering angle cannot be actively controlled, and tuning for obtaining an ideal balance between them is difficult. There was a problem.
SUMMARY OF THE INVENTION An object of the present invention is to provide an electric power steering device that can be easily tuned to balance operation torque and steering angle of a steering mechanism.

  In order to achieve the above object, the invention according to claim 1 is directed to assist steering by transmitting the power of the electric motor (M) driven in accordance with the operation of the operation members (1, 2) to the steering mechanism (3). An electric power steering device for operating the operating member, an operating angle detecting unit (16) for detecting an operating angle of the operating member, a torque detecting unit (15) for detecting an operating torque applied to the operating member, and the operating angle detection An operation member side reference model (31) for determining a target operation torque based on an operation angle detected by the means, and a steering mechanism side for determining a target steering angle of the steering mechanism based on the operation torque detected by the torque detection means And a control means (10) including a reference model (32) and drivingly controlling the electric motor based on the operating member side reference model and the steering mechanism side reference model. An electric power steering device that. The alphanumeric characters in parentheses indicate corresponding components in the embodiments described later.

  According to this configuration, the relationship between the operation angle and the target operation torque is determined by the operating member side reference model, and the relationship between the operation torque and the target steering angle is determined by the steering mechanism side reference model. Accordingly, the relationship between the operating torque and the steering angle of the steering mechanism is directly adjusted by tuning the reference model on the operating member side and the reference model on the steering mechanism side and the balance of the contribution (gain) to the control of both models. be able to. Therefore, tuning of the relationship between the operating torque and the steering angle of the steering mechanism can be facilitated.

  The operation member side reference model may determine a target operation torque based on an operation angle detected by the operation angle detection unit and an operation angular velocity which is a change rate of the operation angle. More specifically, the operating member side reference model multiplies the operating angle by a predetermined first coefficient (spring coefficient) and the operating angular velocity by a predetermined second coefficient (viscosity coefficient). The target operation torque may be determined by adding the obtained values. In this case, the relationship between the operation angle and the target operation torque can be adjusted by changing the first and / or second coefficients.

Further, the steering mechanism side reference model is obtained from the inertia moment J of the operation member, the viscosity coefficient C (friction coefficient) corresponding to the friction when the steering mechanism is operated, and the spring coefficient K when the operation member is regarded as a spring. The target rudder angle with respect to the operating torque may be determined by the secondary delay element 1 / (Js ² + Cs + K). Specifically, by tuning the coefficients C and K, the relationship between the operating torque and the target rudder angle can be directly adjusted. In this case, the transient response characteristic of the target rudder angle with respect to the change in the operating torque is adjusted.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a diagram for explaining a basic configuration of an electric power steering apparatus according to an embodiment of the present invention. The operating torque T applied to the steering wheel 1 is transmitted to the steering mechanism 3 via the steering shaft 2. A driving force generated by the electric motor M is mechanically transmitted to the steering mechanism 3 via the reduction gear 5 as a steering assist force.

  The steering shaft 2 is divided into an input shaft 2a coupled to the steering wheel 1 side and an output shaft 2b coupled to the steering mechanism 3 side. The input shaft 2a and the output shaft 2b are connected to the torsion bar 4. Are connected to each other. The torsion bar 4 is twisted according to the operation torque T applied to the steering wheel 1, and the direction and amount of the twist are detected by a torque sensor 15 as torque detecting means. . The output signal of the torque sensor 15 is input to a controller 10 (ECU: electronic control unit) as control means.

The input shaft 2 a is provided with an operation angle sensor 16 that is an operation angle detection means for detecting the rotation angle of the input shaft 2 a as the operation angle θh of the steering wheel 1. The operation angle θh detected by the operation angle sensor 16 is input to the controller 10.
The output shaft 2 b is coupled to the rack and pinion mechanism 7. The rack and pinion mechanism 7 has a pinion 8 coupled to the output shaft 2b and a rack shaft 9 meshing with the pinion 8. The rack shaft 9 extends in the left-right direction of the vehicle and is slidably held in a housing (not shown). Steering wheels 12 and 12 are coupled to both ends of the rack shaft 9 via a connecting member 11 including a tie rod and a knuckle arm. With this configuration, the rack shaft 9 linearly moves in the left-right direction of the vehicle as the output shaft 2b rotates, and the directions of the steering wheels 12, 12 change accordingly. The reduction gear 5 may transmit the rotation of the electric motor M to the output shaft 2b, for example.

In addition to the outputs of the torque sensor 15 and the operation angle sensor 16, the controller 10 detects the rotation angle of the output shaft 2 b to detect the steering angle (wheel steering angle) θw that is the direction of the steering wheels 12, 12. The output signal of the wheel steering angle sensor 18 for detecting the above is also input.
FIG. 2 is a block diagram for explaining an internal configuration of the controller 10. The controller 10 is a control for controlling the electric motor M based on the operation torque T detected by the torque sensor 15, the operation angle θh detected by the operation angle sensor 16, and the wheel steering angle θw detected by the wheel steering angle sensor 18. A microcomputer 20 that generates a signal, a drive signal generation circuit 21 that receives a control signal from the microcomputer 20 and generates a PWM (pulse width modulation) drive signal, and a drive signal from the drive signal generation circuit 21 A driver circuit 22 having a switching element to be operated and supplying electric power corresponding to the control signal to the electric motor M is provided.

  The microcomputer 20 substantially includes a plurality of function processing units realized by executing a predetermined program stored in an internal memory (not shown). These function processing units include an upstream reference model (operation member side reference model) 31 that determines a target operation torque Tr that is an operation torque to be felt by the driver via the steering wheel 1 based on the operation angle θh, and A downstream reference model (steering mechanism side reference model) 32 that determines the target wheel steering angle θwr of the steering wheels 12 and 12 based on the operation torque T detected by the torque sensor 15 is included.

  Further, the function processing unit includes a torque deviation calculation unit 33 for obtaining a deviation of the actual operation torque T with respect to the target operation torque Tr determined by the upstream reference model 31, and a deviation obtained by the torque deviation calculation unit 33. A first PID (proportional integral derivative) control unit 34 for generating a control signal in response to the steering angle deviation calculating unit for obtaining a deviation of the actual wheel steering angle θw from the target wheel steering angle θwr determined by the downstream reference model 32 35, a second PID control unit 36 that generates a control signal according to the deviation obtained by the rudder angle deviation calculation unit 35, and an addition calculation that adds the control signals generated by the first and second PID control units 34 and 36 And an amplifying unit 38 that applies a gain to the control signal synthesized by the addition calculating unit 37. The control signal after gain adjustment by the amplifier 38 is supplied to the drive signal generation circuit 21.

  With such a configuration, the first PID control unit 34 generates a control signal so that the target operation torque Tr determined by the upstream reference model 31 is achieved, and the second PID control unit 36 has the downstream reference model 32 A control signal is generated so that a predetermined target wheel steering angle θwr is achieved. In this way, the operation torque T and the steering angle θw of the steering wheels 12, 12 can be directly feedback controlled.

  Then, by appropriately determining the proportional gain, integral gain, and differential gain in the first PID control unit 34 and the second PID control unit 36, between the control based on the upstream reference model 31 and the control based on the downstream reference model 32. Appropriate balance weighting is possible. Further, by adjusting the gain in the amplifying unit 38, the steering assist force applied from the electric motor M to the steering mechanism 3 can be increased or decreased, so that the steering wheels 12 and 12 can be passed through the steering mechanism 3 to the steering wheel 1. The road surface reaction force transmitted can be adjusted. Thereby, a road surface condition etc. can be appropriately transmitted to a driver.

  For adjusting the gain in the first and second PID control units 34 and 36 and the amplification unit 38, for example, a tuning tool (for example, a personal computer installed with a tuning program) is connected to the controller 10, and the tuning tool is connected to the controller 10. On the other hand, this can be done by setting a control constant that determines the gain.

  The downstream reference model 32 is provided with the steering angular speed of the steering wheels 12 and 12 and other various vehicle information (for example, the yaw rate of the vehicle, brake information, the steering midpoint obtained from the attitude control unit, etc.). Also good. That is, the downstream reference model 32 may determine the target wheel steering angle θwr based not only on the operation torque T but also on the tire steering angular speed and other vehicle information.

  FIG. 3 is a functional block diagram illustrating an example of the upstream reference model 31. The upstream reference model 31 includes a spring coefficient multiplier 41 that multiplies the operating angle θh by a spring coefficient K1, an operating angular speed calculator 42 that obtains the operating angular speed θh ′ by differentiating the operating angle θh with respect to time, and the operating angular speed. A viscosity coefficient multiplier 43 that multiplies the operation angular velocity θh ′ obtained by the calculator 42 by the viscosity coefficient C1; and an addition calculator 44 that adds the output of the spring coefficient multiplier 41 and the output of the viscosity coefficient multiplier 43. ing. The output of the addition calculation unit 44 becomes the target operation torque Tr. In the upstream reference model 31, the relationship between the operation angle θh and the target operation torque Tr can be adjusted by adjusting the spring coefficient K1 and / or the viscosity coefficient C1, and an appropriate steering feeling can be easily realized. it can.

  FIG. 4 is a diagram for explaining tuning of the upstream reference model 31. FIG. 4 shows the relationship between the operation angle θh and the target operation torque Tr when the steering wheel 1 is operated left and right. That is, on the coordinate plane with the operation angle θh as the horizontal axis and the target operation torque Tr as the vertical axis, the relationship between the operation angle θh and the target operation torque Tr is an ellipse with the straight line 45 passing through the origin as the major axis. Eggplant. By changing the spring coefficient K1, the slope of the straight line 45 changes, and by changing the viscosity coefficient C1, the ellipse expands / contracts in the vertical direction (the coordinate axis direction of the target operation torque Tr). In this way, the relationship between the operation angle θh and the target operation torque Tr can be freely changed by adjusting the spring coefficient K1 and the viscosity coefficient C1.

  FIG. 5 is a block diagram illustrating a configuration example of the downstream reference model 32. The downstream reference model 32 includes a moment of inertia J of the operation members (the steering wheel 1 and the steering shaft 2), a viscosity coefficient C (friction coefficient) corresponding to the friction of the rack shaft 9 with respect to the housing, and the operation member as a spring. This model is based on the fact that the operating torque T is expressed by the following equation based on the spring coefficient K when considered.

T = Jθw ″ + Cθw ′ + Kθw
That is, the operating torque T is obtained by multiplying the second-order time differential value θw ″ of the wheel rudder angle θw by the moment of inertia J, and multiplying the first-order time derivative value θw ′ of the wheel rudder angle θw by the viscosity coefficient C, thereby obtaining the wheel rudder angle θw. This is obtained by multiplying by the spring coefficient K. In other words, the downstream reference model 32 is represented by the second-order lag element 1 / (Js ² + Cs + K), where s is Laplace. It is an operator.

  A more specific configuration will be described. The downstream-side reference model 32 includes an inertia term calculation unit 51 that multiplies the operation torque T by the reciprocal of the inertia moment J, and a first that integrates the calculation result of the inertia term calculation unit 51. Integration unit 52, a second integration unit 53 that further integrates the calculation result of the first integration unit 52, and a viscosity term calculation unit 54 that multiplies the calculation result of the first integration unit 52 by the viscosity coefficient C. A spring term calculation unit 55 that multiplies the calculation result of the second integration unit 53 by a spring coefficient K, and a subtraction unit 56 that subtracts the calculation results of the viscosity term calculation unit 54 and the spring term calculation unit 55 from the operation torque T. And. And the calculation result by the 2nd integration part 53 is made into the target wheel steering angle (theta) wr.

  FIG. 6 is a diagram for explaining the tuning of the downstream reference model 32 as described above. FIG. 6 (a) shows the change over time of the wheel steering angle θw, and FIG. Shows time change. Since the downstream reference model 32 shown in FIG. 5 is a model represented by a second-order lag element as described above, the wheel rudder with respect to the step-like change in the operating torque T as shown in FIG. As shown in FIG. 6 (a), the angle θw rises gently, and shows a transient response that gradually converges to a constant value with overshoot / undershoot.

In the downstream reference model 32, the transient response characteristic can be changed by adjusting the moment of inertia J, the viscosity coefficient C, and / or the spring coefficient K. In this way, the desired steering characteristics can be realized by directly tuning the relationship between the operating torque T and the target wheel steering angle θwr.
The coefficients K1, C1, J, C, and K can be set for the controller 10 using the above-described tuning tool, so that the upstream reference model 31 and the downstream reference model 32 can be tuned. .

  Although one embodiment of the present invention has been described above, the present invention can be implemented in other forms, and various design changes can be made within the scope of matters described in the claims.

It is a figure for demonstrating the basic composition of the electric power steering device concerning one embodiment of this invention. It is a block diagram for demonstrating the functional structure of the controller of the said electric power steering apparatus. It is a block diagram which shows an example of an upstream reference model. It is a figure for demonstrating tuning of an upstream reference model. It is a block diagram which shows an example of a downstream normative model. It is a figure for demonstrating tuning of a downstream reference model.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Steering wheel, 2 ... Steering shaft, 3 ... Steering mechanism, 12 ... Steering wheel, 20 ... Microcomputer, 37 ... Addition calculating part, 38 ... Amplifying part, 41 ... Spring coefficient multiplication part, 42 ... Operation angular velocity calculating part, DESCRIPTION OF SYMBOLS 43 ... Viscosity coefficient multiplication part, 44 ... Addition calculating part, 51 ... Inertia term calculating part, 52, 53 ... Integration part, 54 ... Viscosity term calculating part, 55 ... Spring term calculating part, 56 ... Subtracting part, M ... Electric motor

Claims (1)

An electric power steering device for assisting steering by transmitting power of an electric motor driven in accordance with an operation of an operation member to a steering mechanism,
An operation angle detection means for detecting an operation angle of the operation member;
Torque detecting means for detecting an operating torque applied to the operating member;
An operation member side reference model that determines a target operation torque based on the operation angle detected by the operation angle detection means, and a steering mechanism that determines a target steering angle of the steering mechanism based on the operation torque detected by the torque detection means An electric power steering apparatus comprising: a side reference model, and control means for driving and controlling the electric motor based on the operating member side reference model and the steering mechanism side reference model.

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