Steering control device

Abstract

To provide a steering control device which prevents rattle sound due to generation of pulse noise even when a gradient change is large at a map break point between an estimated load torque and a target steering torque.SOLUTION: A servo controller 400 calculates a base assist command Tb* so that a steering torque Ts follows a target steering torque Ts*. An estimated load torque calculation part calculates an estimated load torque on the basis of the target steering torque Ts* and the base assist command Tb*. A target steering torque calculation part calculates the target steering torque Ts* using a map specifying a relation between the estimated load torque and the target steering torque Ts*. The servo controller 400 has a low-pass filter 51 for removing a high frequency component of a predetermined frequency or higher in the input target steering torque Ts* in at least differential control calculation, and calculates a differential control amount according to a steering torque deviation ΔT2 between the target steering torque Ts* and the steering torque Ts after the low-pass filter 51.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a steering control device. [Background technology]

[0002] Conventionally, in a steering device that controls the assist torque output by a motor, a technology is known in which a target steering torque is calculated based on an estimated load torque, and a base assist command is calculated by a servo controller so that the steering torque follows the target steering torque.

[0003] For example, in the steering control device disclosed in Patent Document 1, a target generating unit generates a target steering torque (Ts * ) and base assist command (Tb * ) to calculate an estimated load torque (road surface reaction force in Patent Document 1). The torque converter of the target generation unit calculates the target steering torque using a map that specifies the value of the target steering torque with respect to the estimated load torque.

[0004] Moreover, in the steering control device disclosed in Patent Document 2, a servo controller (assist controller in Patent Document 2) generates a base assist command by PID control so that the steering torque follows a target steering torque. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6314752 [Patent Document 2] Patent No. 6252027 Summary of the Invention [Problem to be solved by the invention]

[0006] The target steering torque is calculated by an interpolation calculation using a map. When the estimated load torque, which is the map input, changes during steering, the output change relative to the input change is constant within the interpolation section, but when passing through the bending point of the map, the gradient changes, causing a sudden change in the time rate of change of the output.

[0007] For example, when a map is adapted to obtain a steering feel or a desired behavior, the gradient change at the map break point may be large, especially in the small signal region where the estimated load torque is close to 0. If the gradient change at the map break point is large, the differential calculation output of the servo controller changes when passing through that point, and as a result, the base assist command changes. Then, pulse noise is generated in the process of calculating the target steering torque for the next calculation cycle using the fed-back base assist command, which may vibrate the motor and cause a rattle noise.

[0008] The present invention was created in consideration of these points, and its purpose is to provide a steering control device that prevents rattle noise caused by the generation of pulse noise even if there is a large change in gradient at the map break point between the estimated load torque and the target steering torque. [Means for solving the problem]

[0009] The present invention provides a steering control device that controls an assist torque output by a motor (80) connected to a steering system mechanism (100) that generates a steering torque (Ts), and includes a servo controller (400), an estimated load torque calculation unit (20), and a target steering torque calculation unit (30).

[0010] The servo controller calculates the steering torque based on the target steering torque (Ts * ) to make the assist torque follow the base assist command (Tb * ) is calculated.

[0011] The estimated load torque calculation unit calculates an estimated load torque (Tx), which is a load torque acting on a steering shaft (95) of a steering system mechanism and which varies in response to steering, based on the steering torque or the target steering torque and the assist torque or the base assist command. The target steering torque calculation unit calculates the target steering torque (Ts * ) is calculated.

[0012] The servo controller has a low-pass filter (51) that removes high-frequency components having a predetermined frequency or higher in the input target steering torque at least in the differential control calculation, and calculates a differential control amount according to the steering torque deviation (ΔT2) between the target steering torque after the low-pass filter and the steering torque.

[0013] As a result, in the present invention, even if the gradient change at the map break point is large, especially in the small signal region, a steep pulse is not superimposed on the base assist command. Therefore, steering vibration such as rattle noise can be prevented, and smooth operation with low vibration can be obtained. Therefore, the degree of freedom in adaptation is increased. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram of an electric power steering system. [Diagram 2] 1 is a schematic configuration diagram of an ECU (steering control device) according to an embodiment. [Diagram 3] FIG. 13 is an enlarged view of a small signal region of the estimated load torque-target steering torque map. [Figure 4] 1A to 1C are diagrams for explaining the principle of occurrence of a problem phenomenon in map calculation. [Diagram 5] A time chart supplementing Figure 4. [Figure 6] FIG. 2 is a block diagram of a servo controller according to an embodiment. [Figure 7] 4 is a time chart showing the behavior of an actual vehicle in a comparative example (normal PID control). [Figure 8] 4 is a time chart showing the behavior of an actual vehicle according to the present embodiment; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] An embodiment of a steering control device of the present invention will be described below with reference to the drawings. An ECU as a "steering control device" is applied to an electric power steering system or a steer-by-wire system of a vehicle, and calculates an output command for a motor. In the following embodiment, an example in which the steering control device is mainly applied to an electric power steering system is shown. In the electric power steering system, the steering control device outputs an assist torque command to a steering assist motor.

[0016] [Electric power steering system configuration] The configuration of the electric power steering system will be described with reference to FIG. 1. The assist torque Ta and the base assist command Tb * For symbols, see Fig. 2. The electric power steering system 1 is a system that assists the driver in operating a steering wheel 91 by using the driving torque of a motor 80. The steering wheel 91 is fixed to one end of a steering shaft 92, and an intermediate shaft 93 is provided on the other end of the steering shaft 92. The steering shaft 92 and the intermediate shaft 93 are connected by a torsion bar of a torque sensor 94, and these form a steering shaft 95. The torque sensor 94 detects the steering torque Ts based on the torsion angle of the torsion bar.

[0017] A gear box 96 including a pinion gear 961 and a rack 962 is provided on the end of the intermediate shaft 93 opposite to the torque sensor 94. When the driver turns the steering wheel 91, the pinion gear 961 rotates together with the intermediate shaft 93, and the rack 962 moves left and right in accordance with the rotation of the pinion gear 961. Tie rods 97 provided on both ends of the rack 962 are connected to tires 99 via knuckle arms 98. The tie rods 97 reciprocate left and right, pulling and pushing the knuckle arms 98, thereby changing the orientation of the tires 99.

[0018] The motor 80 is, for example, a three-phase AC brushless motor, and outputs an assist torque Ta that assists the steering force of the steering wheel 91 in response to a drive voltage Vd output from the ECU 10. In the case of a three-phase AC motor, the drive voltage Vd means the voltage of each of the U-phase, V-phase, and W-phase. The rotation of the motor 80 is transmitted to an intermediate shaft 93 via a reduction mechanism 85 constituted by a worm gear 86, a worm wheel 87, and the like. In addition, the rotation of the intermediate shaft 93 caused by the steering of the steering wheel 91 or a reaction force from the road surface is transmitted to the motor 80 via the reduction mechanism 85.

[0019] 1 is a column assist type in which the rotation of the motor 80 is transmitted to the steering shaft 95, but the ECU 10 of this embodiment is similarly applicable to a rack assist type electric power steering system. In other embodiments, a polyphase AC motor other than a three-phase motor or a brushed DC motor may be used as the steering assist motor.

[0020] Here, the entire mechanism through which the steering force of the steering wheel 91 is transmitted from the steering wheel 91 to the tires 99 is referred to as the "steering system mechanism 100." The ECU 10 controls the assist torque Ta output by the motor 80 connected to the steering system mechanism 100, thereby controlling the steering torque Ts generated by the steering system mechanism 100. The ECU 10 also acquires the vehicle speed V detected by a vehicle speed sensor 11 provided at a predetermined location on the vehicle.

[0021] The ECU 10 operates on power from an on-board battery (not shown) and generates a base assist command Tb, which is a basic command value of the assist torque, based on the steering torque Ts detected by the torque sensor 94 and the vehicle speed V detected by the vehicle speed sensor 11. * In this embodiment, the base assist command Tb * No correction torque is added to the base assist command Tb * is output as it is as a command value for the assist torque Ta.

[0022] Base assist command Tb * The drive voltage Vd calculated based on this is applied to the motor 80, causing the motor 80 to output the assist torque Ta, and causing the steering mechanism 100 to generate a steering torque Ts. Note that the various calculation processes in the ECU 10 may be software processes in which a CPU executes a program pre-stored in a physical memory device such as a ROM, or may be hardware processes in which a dedicated electronic circuit is used.

[0023] [ECU configuration] (One embodiment) The configuration of the ECU 10 according to one embodiment will be described with reference to Fig. 2. The ECU 10 includes an estimated load torque calculation unit 20, a target steering torque calculation unit 30, a servo controller 400, and a current feedback ("FB" in the figure) unit 70.

[0024] The estimated load torque calculation unit 20 calculates the target steering torque Ts * and base assist command Tb * The estimated load torque Tx is a load torque that acts on the steering shaft 95 of the steering system mechanism 100 and changes in response to steering. The positive and negative of the estimated load torque Tx and the steering torque Ts are defined according to the rotation direction of the steering shaft 95 such that the torque in one rotation direction is positive and the torque in the opposite direction is negative.

[0025] The estimated load torque calculation unit 20 includes an adder 21 and a low-pass filter ("LPF" in the figure) 22. The adder 21 receives a base assist command Tb * and the target steering torque Ts fed back from the target steering torque calculation unit 30. * Add and.

[0026] The low-pass filter 22 extracts a predetermined frequency component, for example a band of 10 Hz or less, from the added torque. The estimated load torque calculation unit 20 outputs the frequency component extracted by the low-pass filter 22 as the estimated load torque Tx.

[0027] The target steering torque calculation unit 30 calculates the estimated load torque Tx and the target steering torque Ts * Using the map 33 in which the relationship between the target steering torque Ts * The target steering torque calculation unit 30 includes a sign determination unit ("sgn" in the figure) 31, an absolute value determination unit ("|u|" in the figure) 32, a map 33, and a multiplier 34. The sign determination unit 31 determines whether the estimated load torque Tx is positive or negative, i.e., the sign according to the rotation direction of the steering shaft 95. The absolute value determination unit 32 calculates the input u, i.e., the absolute value of the estimated load torque Tx.

[0028] The map 33 is shown as a map in the positive region of the estimated load torque Tx, that is, as a map of the absolute value. In the negative region of the estimated load torque Tx, the map is symmetrical with respect to the origin with respect to the positive region. * has a positive correlation with the estimated load torque Tx and increases logarithmically as the estimated load torque Tx increases.

[0029] Specifically, the map 33 is a graph showing the target steering torque Ts for a specific value of the estimated load torque Tx for each vehicle speed V. * The target steering torque Ts for any estimated load torque Tx is expressed by a broken line connecting multiple points indicating the value of * is obtained by an interpolation calculation of the map 33. The higher the vehicle speed V, the lower the target steering torque Ts for the same estimated load torque Tx. * The horizontal axis of the map 33, which is the estimated load torque Tx, ranges from about 0 to 30 [Nm], and the target steering torque Ts * The range is approximately 0 to 6 [Nm].

[0030] FIG. 3 shows an enlarged view of the small signal region where the estimated load torque Tx is close to 0 in the map 33 in FIG. 2. This map 33 is adapted in the small signal region to obtain a steering feel and a desired behavior. As a result of the adaptation, at the turning point of the estimated load torque Tx of 0.3 [Nm], the target steering torque Ts *The rate of change of the target steering torque Ts is increasing, and the bend is large. At other bends, the second-order differential value is negative, whereas at this bend, the second-order differential value is positive. Also, at the bend where the estimated load torque Tx is 1 [Nm], the target steering torque Ts * The rate of change of the curve suddenly decreases, and the curve is large. The influence of the large curve at the break point will be described later with reference to Figs. 4 and 5.

[0031] Returning to FIG. 2, the target steering torque Ts calculated based on the absolute value of the estimated load torque Tx is * The absolute value of the target steering torque Ts outputted from the target steering torque calculation unit 30 is multiplied by a sign corresponding to the sign of the estimated load torque Tx in a multiplier 34. * is input to the servo controller 400 and is also fed back to the estimated load torque calculation unit 20.

[0032] The servo controller 400 has a target steering torque Ts * and steering torque Ts are input. The servo controller 400 converts the steering torque Ts into a target steering torque Ts * The base assist command Tb * A detailed configuration of the servo controller 400 of this embodiment will be described later with reference to FIG.

[0033] The current feedback unit 70 outputs the base assist command Tb * A drive voltage Vd is applied to the motor 80 so that an assist torque corresponding to the torque is applied to the steering shaft 95, which is closer to the tire 99 than the torque sensor 94. The current feedback control technology is well known in the field of motor control, and therefore a detailed description thereof will be omitted.

[0034] Next, the principle of occurrence of the problem phenomenon in the map calculation of the target steering torque calculation unit 30 will be described with reference to Fig. 4 and Fig. 5. *The figure shows a schematic diagram of a map of the estimated load torque Tx and the steering torque deviation. As shown by the dashed arrow, consider the case where the estimated load torque Tx increases monotonically and the operating point on the map progresses from point A to point B. In the explanation of Figures 4 and 5, the symbol for the steering torque deviation is "ΔT", which assumes normal PID control.

[0035] If the estimated load torque Tx increases linearly, the target steering torque Ts * , and the differential of the target steering torque D(Ts * ) changes as shown in the time waveform in FIG. 5. In this case, the differential D(Ts * ), that is, the gradient change of the map is a step change rather than a pulse change. However, the base assist command Tb * When a closed loop is formed in which the load torque is fed back to the estimated load torque calculation unit 20, the following phenomenon occurs.

[0036] When the estimated load torque Tx changes from time n to the next time (n+1) in FIG. 4, the signal that has passed through the servo controller 400 mainly undergoes a relatively large step change in the differential control component. At this time, when the estimated load torque Tx increases, the steering torque deviation ΔT increases and the steering torque deviation differential D(ΔT) becomes positive. Also, since the differential gain Kd in the PID control equation is negative as described later, the base assist command Tb * is on the decline.

[0037] Then, at the next time (n+2), the reduced base assist command Tb * The estimated load torque Tx calculated based on the estimated load torque Tx is reduced. * is smaller than the previous value at time (n+1). Therefore, the differential D(Ts * The derivative of Tb changes the step change in the previous direction, resulting in a pulse. This is the base assist command Tb * This appears as pulse noise.

[0038] In this way, when the gradient change at the map breakpoint is large, especially in the small signal region, the base assist command Tb * The motor 80 may be vibrated by pulse noise appearing in the map, which may cause rattle noise. Here, it is possible that the noise vibration may be eliminated by adapting the map so that the map has a high score and changes smoothly. However, it is necessary to repeat adaptation and noise vibration evaluation through trial and error, which imposes restrictions on the adaptation. Therefore, in this embodiment, the estimated load torque Tx and the target steering torque Ts * To prevent rattle noise caused by pulse noise even if the gradient change at the map break point is large.

[0039] To solve this problem, the configuration of a servo controller 400 according to this embodiment is shown in Fig. 6. The servo controller 400 includes a PID controller 410, an accumulation calculation unit 490, and a low-pass filter 51. Fig. 6 shows a configuration in which the servo control calculation is equivalently converted into a discrete equation.

[0040] The proportional control calculation unit 430 and the integral control calculation unit 440 of the PID controller 410 calculate the target steering torque Ts * The deviation calculator 42 performs proportional and integral control calculations based on the steering torque deviation ΔT1 between the target steering torque Ts * and the steering torque Ts, a steering torque deviation ΔT1 is calculated.

[0041] The delay element 45 extracts the previous value of the steering torque deviation ΔT1. In the proportional control calculation unit 430, the steering torque deviation ΔT1 from which the previous value has been subtracted in the subtractor 463 is multiplied by a proportional gain Kp in the gain multiplier 473. In the integral control calculation unit 440, the steering torque deviation ΔT1 from which the previous value has been added in the adder 464 is multiplied by an integral gain Ki in the gain multiplier 474.

[0042] The differential control calculation unit 50, which is a configuration specific to this embodiment, calculates the target steering torque Ts * The differential target steering torque LPF (Ts *The low-pass filter 51 calculates a differential control amount according to the steering torque deviation ΔT2 between the input target steering torque Ts * The high frequency components above a certain frequency are removed from the differential target steering torque LPF (Ts * ) is output. "LPF" indicates a function that performs a first-order low-pass filter process. The deviation calculator 52 outputs the differential target steering torque LPF (Ts * ) and the steering torque Ts, a steering torque deviation ΔT2 is calculated.

[0043] The pseudo differential calculation unit 54 calculates the steering torque deviation differential D(ΔT2) by pseudo differentiation. The pseudo differential "D" of the discrete value is expressed as (s / (τs+1)) in terms of a transfer function of the continuous system. 2 ) (where s is a Laplace operator and τ is a time constant). A delay element 55 extracts the previous value of the steering torque deviation differential D(ΔT2). In the differential control calculation unit 50, the steering torque deviation differential D(ΔT2) from which the previous value has been subtracted by a subtractor 56 is multiplied by a differential gain Kd in a gain multiplier 57.

[0044] The PID component adder 48 outputs the target torque TM obtained by adding up the components of the PID control for each control period. The accumulation processing unit 490 accumulates the target torque TM and outputs the current value Tb of the base assist command. * n Accumulation processing is synonymous with integral processing, but the term "accumulation" is used here to distinguish it from PID integral control. Although there are differences depending on the calculation configuration of the servo controller, the point is to output the calculation signal of the PID controller.

[0045] The accumulation processing unit 490 includes an adder 491, a delay element 492, and a limiting calculator 494. The adder 491 multiplies the current value of the torque TM to be processed by the previous value Tb of the base assist command input via the delay element 492. * n-1The limiting calculator 494 limits the sum of the adder 491 to a limiting value that can be output as an assist torque. This addresses the wind-up problem, that is, the phenomenon in which, when a deviation continues to occur, a value larger than the allowable output is taken by integration, and then when the sign of the deviation reverses, the reduction in output is delayed.

[0046] The servo control formulas are shown below. The steering torque deviations ΔT1 and ΔT2 are expressed by formulas (1.1) and (1.2), respectively. ΔT1=Ts * -Ts (1.1) ΔT2=LPF(Ts * )-Ts (1.2)

[0047] Base assist command Tb * is expressed by the formula (2). In the configuration of Fig. 6, the proportional gain Kp, the integral gain Ki, and the differential gain Kd are all set to negative values.

[0048]

number

[0049] In order to discretize equation (2), the bilinear transformation equation expressed by equation (3) is substituted into equation (2) and rearranged to obtain equation (4). In equation (3), ts indicates the calculation period. In Figure 6, (ts / 2)Ki is collectively written as "Ki".

[0050]

number

[0051] As described above, the servo controller 400 of this embodiment calculates the input target steering torque Ts * The servo controller 400 includes a low-pass filter 51 that removes high-frequency components having a predetermined frequency or higher in the target steering torque Ts *and the steering torque Ts, a differential control amount corresponding to the steering torque deviation ΔT2 is calculated.

[0052] As a result, the target steering torque Ts used in the differential control calculation * is smoothed by the processing of the low-pass filter 51, the step change of the differential control component is suppressed. Therefore, the step change is less likely to circulate in the closed loop and is less likely to appear as pulse noise. Therefore, the vibration of the motor 80 is suppressed.

[0053] Next, referring to the time charts of Figures 7 and 8, the actual vehicle behavior when the steering wheel is turned left or right so that the steering torque Ts changes from positive to negative and from negative to positive in the comparative example and this embodiment will be described. * This is a normal PID control that does not use a low-pass filter. The discrete equation for normal PID control is shown in equation (5).

[0054]

number

[0055] 7 and 8 show, from top to bottom, the steering angular velocity ω, the steering torque Ts, and the target steering torque Ts * , steering torque deviation differential D(ΔT2) (steering torque deviation differential D(ΔT) in the comparative example), and base assist command Tb * Shows.

[0056] In the comparative example shown in FIG. 7, the target steering torque Ts * When the target steering torque Ts passes through the bending point of the map (Fig. 3) in the small signal region near 0, * At this time, the differential control component in the fourth term of equation (5) changes stepwise. The stepwise change is the base assist command Tb * This is also reflected in the

[0057] This base assist command Tb *When the load torque is fed back to the estimated load torque calculation unit 20, the target steering torque Ts * As a result, the target steering torque Ts * As shown in (*1) and (*2), the steering torque deviation differential D(ΔT) and the base assist command Tb * This results in a pulse-like vibration of the motor 80.

[0058] The effect of the excitation by the pulse current also affects the steering angular velocity ω converted from the motor rotation angle, and as shown in (*3), the waveform fluctuates. In addition, when focusing on the direction of the excitation, it is opposite to the direction in which the motor 80 is intended to rotate. Therefore, it acts in the opposite direction by passing through the gear backlash and play, which tends to cause rattle noise.

[0059] In this embodiment shown in FIG. 8, the target steering torque Ts * When the map passes the bending point, the target steering torque Ts * Even if the change in the target steering torque Ts used in the differential control calculation becomes large, * Since is smoothed by the processing of the low-pass filter 51, step-like changes in the derivative control component are suppressed.

[0060] Therefore, the base assist command Tb obtained by accumulating the formula (4) * is free of pulse noise. Furthermore, the base assist command Tb * The target steering torque Ts is calculated based on the estimated load torque Tx. * The base assist command Tb is determined in the circulatory system where * As a result, in this embodiment, no rattle noise is generated, and smooth actuator operation with low noise is achieved.

[0061] (Other embodiments) (a) Target steering torque Ts *A low-pass filter that filters is provided at least in the differential control calculation. In other embodiments, a low-pass filter may be provided in the proportional control calculation or the integral control calculation in addition to the differential control calculation.

[0062] (b) The estimated load torque calculation unit 20 calculates the target steering torque Ts * Based on the steering torque Ts instead of the base assist command Tb * Instead, the estimated load torque Tx may be calculated based on the assist torque Ta. As the detected value of the assist torque Ta, a value obtained by converting the motor detection current input to the current feedback unit 70 in FIG. 2 into a torque around the steering shaft can be used.

[0063] However, the correction torque command by convergence control, steering angle control, etc. is the base assist command Tb * In a configuration in which the assist torque command is obtained by adding the base assist command Tb to the base assist command Tb, the effect of the correction torque command may be lost if the assist torque is used to calculate the estimated load torque Tx. * It is preferable to calculate the estimated load torque Tx based on the above.

[0064] (c) Target steering torque Ts * is not limited to being calculated based on the estimated load torque Tx, but may be added with a steering torque according to other state quantities such as a steering angle and a steering angular velocity, or may be corrected according to other state quantities. For example, Japanese Patent No. 6387657 discloses a configuration example in which a steering angle reference correction torque is added to the estimated load torque.

[0065] The present invention is not limited to such an embodiment, and can be embodied in various forms without departing from the spirit of the present invention.

[0066] The controller and the method described in the present disclosure may be implemented by a special-purpose computer provided by configuring a processor and a memory programmed to execute one or more functions embodied in a computer program. Alternatively, the controller and the method described in the present disclosure may be implemented by a special-purpose computer provided by configuring a processor with one or more dedicated hardware logic circuits. Alternatively, the controller and the method described in the present disclosure may be implemented by one or more special-purpose computers configured by a combination of a processor and a memory programmed to execute one or more functions and a processor configured with one or more hardware logic circuits. The computer program may also be stored in a computer-readable non-transitory tangible recording medium as instructions executed by a computer. [Explanation of symbols]

[0067] 10 ECU (steering control unit), 20: Estimated load torque calculation unit, 30 target steering torque calculation unit; 33 map; 400 Servo controller, 51 Low-pass filter, 80 Motor, 95···Steering shaft, 100···Steering system mechanism.

Claims

[Claim 1] A steering control device that controls an assist torque output by a motor (80) connected to a steering mechanism (100) that generates a steering torque (Ts), The steering torque is set to the target steering torque (Ts * ) so that the base assist command (Tb * A servo controller (400) for calculating an estimated load torque calculation unit (20) for calculating an estimated load torque (Tx), which is a load torque acting on a steering shaft (95) of the steering system mechanism and which varies in response to steering, based on a steering torque or the target steering torque, and an assist torque or the base assist command; The target steering torque (Ts * a target steering torque calculation unit (30) for calculating a target steering torque; Equipped with The servo controller includes: a low-pass filter (51) for removing high-frequency components having a predetermined frequency or higher in the input target steering torque at least in a differential control calculation; A steering control device that calculates a differential control amount corresponding to a steering torque deviation (ΔT2) between the target steering torque and the steering torque after the low-pass filter.

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