JP2023016624A - steering control device - Google Patents

Abstract

To provide a steering control device that prevents a handle from being pushed back when the absolute value of steering torque is saturated.SOLUTION: A servo controller 400 calculates an output command (a base assist command) Tb* of a motor 80 so as to cause steering torque Ts to follow target steering torque Ts*. A steering torque saturation determination unit 38 determines that an absolute value |Ts| of steering torque is saturated. When the steering torque saturation determination unit 38 determines that the absolute value |Ts| of the steering torque is saturated, the servo controller 400 resets a differential component calculation for PID control as "a calculation for an element related to assist torque with which a phase has advanced with respect to the steering torque". Specifically, the servo controller 400 performs a calculation by using 0 instead of an original input value, or performs a calculation by using a result obtained by clearing a stored past value to 0.SELECTED DRAWING: Figure 2

Description

The present invention relates to steering control devices.

2. Description of the Related Art Conventionally, in a steering device that controls assist torque output by a motor, a technique is known in which a motor output command is calculated by a servo controller so that the steering torque follows a target steering torque.

For example, in the steering control device disclosed in Patent Document 1, a servo controller (assist controller in Patent Document 1) generates a base assist command through PID control so that the steering torque follows the target steering torque.

Japanese Patent No. 6252027

When the absolute value of the steering torque saturates due to sudden steering or hitting the rack end, the differential component of PID control gives a large change in the assist torque to the side pushing back the steering wheel. As a result, when it saturates with sudden steering, it becomes heavy for a moment, and when it hits the end, there is a risk that it will bounce back.

SUMMARY OF THE INVENTION The present invention has been created in view of such a point, and its object is to provide a steering control device that prevents the steering wheel from being pushed back when the absolute value of the steering torque is saturated. .

The steering control device of the present invention comprises a servo controller (400) and a steering torque saturation determination section (38). The servo controller calculates an output command (Tb ^* ) for the motor (80) so that the steering torque follows the target steering torque (Ts ^* ). The steering torque saturation determination section determines that the absolute value of the steering torque is saturated.

When the steering torque saturation determining section determines that the absolute value of the steering torque is saturated, the servo controller resets the calculation of the elements related to the assist torque whose phase is ahead of the steering torque.

For example, the servo controller performs PID control, and when the steering torque saturation determination section determines that the absolute value of the steering torque is saturated, the servo controller resets the differential component calculation of the PID control. . Specifically, the servo controller resets at least the input to the low-pass filter (54) in the differential component calculation and the past values stored in the low-pass filter.

As a specific configuration for resetting the calculation, it is possible to adopt a configuration in which calculation is performed using 0 instead of the original input value, or calculation is performed using the result of clearing the stored past value to 0.

In the present invention, when the absolute value of the steering torque is saturated, the "element related to the assist torque whose phase is advanced with respect to the steering torque (for example, the differential component of PID control)" becomes 0, so that the steering wheel is pushed back. No torque is generated, and you can steer without being pushed back. Therefore, even if it saturates with sudden steering, it is eliminated that it becomes heavy for a moment. Also, when it hits the end, the handle will stop at that position without being bounced back.

1 is a schematic configuration diagram of an electric power steering system; FIG. 1 is a schematic configuration diagram of an ECU (steering control device) according to one embodiment; FIG. 1 is a block diagram of a servo controller in one embodiment; FIG. FIG. 4 is a detailed block diagram of a differential component calculator in FIG. 3; (a) Comparative example, (b) diagrams showing the operation of servo control calculation according to the present embodiment. The time chart which shows the actual vehicle behavior of a comparative example. A time chart showing actual vehicle behavior of the present embodiment.

An embodiment of the 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 a motor output command. The following embodiments mainly show examples applied to an electric power steering system. In an electric power steering system, a steering control device outputs an assist torque command to a steering assist motor.

[Configuration of electric power steering system]
The configuration of the electric power steering system will be described with reference to FIG. For symbols of the assist torque Ta and the commands Ta ^* and Tb ^* , refer to FIG. The electric power steering system 1 is a system that assists the operation of the steering wheel 91 by the driver with the drive torque of the motor 80 . A handle 91 is fixed to one end of the steering shaft 92 , and an intermediate shaft 93 is provided to 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 a steering shaft 95 is constructed by these. A torque sensor 94 detects the steering torque Ts based on the twist angle of the torsion bar.

A gear box 96 including a pinion gear 961 and a rack 962 is provided at the end of the intermediate shaft 93 opposite to the torque sensor 94 . When the driver turns the handle 91 , the pinion gear 961 rotates together with the intermediate shaft 93 , and the rack 962 moves left and right along with the rotation of the pinion gear 961 . Tie rods 97 provided at both ends of rack 962 are connected to tires 99 via knuckle arms 98 . The direction of the tire 99 is changed by the tie rod 97 reciprocating left and right and pulling or pushing the knuckle arm 98 .

The motor 80 is, for example, a three-phase AC brushless motor, and outputs an assist torque Ta for assisting the steering force of the steering wheel 91 according to the drive voltage Vd output from the ECU 10 . In the case of a three-phase AC motor, the drive voltage Vd means the voltages of the U-phase, V-phase, and W-phase. Rotation of the motor 80 is transmitted to the intermediate shaft 93 via a reduction mechanism 85 composed of a worm gear 86, a worm wheel 87, and the like. Steering of the steering wheel 91 and rotation of the intermediate shaft 93 due to reaction force from the road surface are transmitted to the motor 80 via the reduction mechanism 85 .

The electric power steering system 1 shown in FIG. 1 is of a column-assist type in which the rotation of the motor 80 is transmitted to the steering shaft 95. applicable to In other embodiments, a multiphase AC motor other than three phases or a DC motor with a brush may be used as the steering assist motor.

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

The ECU 10 operates with power from an on-vehicle battery (not shown), and calculates an assist torque command Ta ^* based on the steering torque Ts detected by the torque sensor 94, the vehicle speed V detected by the vehicle speed sensor 11, and the like. Then, the ECU 10 applies the driving voltage Vd calculated based on the assist torque command Ta ^* to the motor 80 to cause the steering system mechanism 100 to generate the steering torque Ts.

Various arithmetic processing in the ECU 10 may be software processing by executing a program stored in advance in a substantial memory device such as a ROM by the CPU, or may be hardware processing by a dedicated electronic circuit. good too.

[Configuration of ECU]
(one embodiment)
The configuration of the ECU 10 according to one embodiment will be described with reference to FIG. The ECU 10 includes an estimated load torque calculation section 20, a target steering torque calculation section 30, a steering torque saturation determination section 38, a servo controller 400, a current feedback ("FB" in the drawing) section 70, and the like.

The estimated load torque calculator 20 calculates the estimated load torque Tx based on the target steering torque Ts ^* and the base assist command Tb ^* . The estimated load torque Tx is a load torque that acts on the steering shaft 95 of the steering mechanism 100 and changes according to steering. Whether the estimated load torque Tx or the steering torque Ts is positive or negative is defined according to the rotational direction of the steering shaft 95 so that the torque in one rotational direction is positive and the torque in the opposite direction is negative.

The estimated load torque calculator 20 includes an adder 21 and a low-pass filter (“LPF” in the figure) 22 . The adder 21 adds the base assist command Tb ^* fed back from the servo controller 400 and the target steering torque Ts ^* fed back from the target steering torque calculator 30 . A low-pass filter 22 extracts components of a predetermined frequency band, for example, 10 Hz or less, from the added torque. The estimated load torque calculator 20 outputs the frequency component extracted by the low-pass filter 22 as the estimated load torque Tx.

The target steering torque calculation unit 30 calculates the target steering torque Ts ^* using a map 33 that defines the relationship between the estimated load torque Tx and 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, that is, the sign according to the rotation direction of the steering shaft 95 . The absolute value determination unit 32 calculates the absolute value of the input u, that is, the estimated load torque Tx.

The map 33 is a map in which the estimated load torque Tx is in a positive region, that is, a map of absolute values. In the negative area of the estimated load torque Tx, the map is symmetrical with respect to the positive area. The multiplier 34 multiplies the map-calculated absolute value of the target steering torque Ts ^* by a sign corresponding to the sign of the estimated load torque Tx. The target steering torque Ts ^* output by the target steering torque calculator 30 is input to the deviation calculator 39 and fed back to the estimated load torque calculator 20 .

A steering torque saturation determination unit 38 determines that the absolute value |Ts| of the steering torque is saturated. Specifically, the steering torque saturation determination section 38 turns ON the steering torque saturation flag when the absolute value |Ts| of the steering torque is equal to or greater than a predetermined steering torque saturation determination threshold. On the other hand, when the absolute value |Ts| of the steering torque is less than the predetermined steering torque saturation determination threshold value, the steering torque saturation flag is turned OFF. A steering torque saturation flag is output to the servo controller 400 .

The steering torque saturation determination threshold is set to the maximum value (eg, 7.5 Nm) of the steering torque absolute value |Ts|. If the signal input to servo controller 400 has undergone any gain correction or limiting treatment, it is preferably set to a value corresponding to its maximum value.

A deviation calculator 39 calculates a steering torque deviation ΔT (=Ts ^* −Ts), which is the difference between the target steering torque Ts ^* and the steering torque Ts. A steering torque deviation ΔT is input to the servo controller 400 . Servo controller 400 calculates base assist command Tb ^* so that steering torque Ts follows target steering torque Ts ^* . A detailed configuration of the servo controller 400 of the present embodiment will be described later with reference to FIGS. 3 and 4. FIG.

In the configuration example of FIG. 2, since the correction torque for the base assist command Tb ^* is not calculated, the base assist command Tb ^* is directly output as the assist torque command Ta ^* . Note that in the configuration in which the correction torque is calculated as shown in FIG. 2 of Patent Document 1 (Japanese Patent No. 6252027), the sum of the base assist command Tb ^* and the correction torque is output as the assist torque command Ta ^*. .

The current feedback unit 70 applies the drive voltage Vd to the motor 80 so that the assist torque corresponding to the base assist command Tb ^* is applied particularly to the steering shaft 95 on the tire 99 side of the torque sensor 94 . The technique of current feedback control is a well-known technique in the field of motor control, so detailed description thereof will be omitted.

3 and 4 show the configuration of the servo controller 400 of this embodiment. 3 and 4 show configurations obtained by equivalently transforming servo control calculations using discrete equations. Servo controller 400 includes a PID controller 410 and an accumulation processor 490 . PID controller 410 includes a proportional component calculator 430, an integral component calculator 440, and a differential component calculator 450, similar to the configuration of the assist controller disclosed in FIG. PID controller 410 performs PID control calculation based on steering torque deviation ΔT.

The delay element 453 of the proportional component calculation section 430 and the delay element 454 of the integral component calculation section 440 take out the previous value of the steering torque deviation ΔT. In proportional component calculation section 430 , steering torque deviation ΔT from which the previous value was subtracted in subtractor 463 is multiplied by proportional gain Kp in proportional gain multiplier 473 . In the integral component calculation unit 440 , the steering torque deviation ΔT to which the previous value was added by the adder 464 is multiplied by the integral gain Ki in the integral gain multiplier 474 .

Pseudo-differential calculation section 50 of differential component calculation section 450 calculates steering torque deviation differential D(ΔT) by pseudo-differentiation. The pseudo-differential "D" of the discrete value corresponds to the operational function of (s/(τs+1) ² ) (where s: Laplace operator, τ: time constant) in terms of the transfer function of a continuous system. A delay element 55 retrieves the previous value of the steering torque deviation differential D(ΔT).

In the differential component calculator 450 , the differential gain Kd is multiplied by the differential gain multiplier 57 to the steering torque deviation differential D(ΔT) from which the previous value was subtracted by the subtractor 56 . The steering torque saturation flag is input to the pseudo-differential calculator 50 and the delay element 55 of the differential component calculator 450, and the "reset process" in the differential component calculation is executed. A detailed configuration of the reset procedure will be described later with reference to FIG.

The PID component adder 48 outputs the torque to be processed TM obtained by adding the proportional component, the integral component and the differential component for each control cycle. The accumulation processing unit 490 accumulates the processing target torque TM and calculates the current value Tb ^* _n of the base assist command. Accumulation processing is synonymous with integration processing, but the term “accumulation” is used here to distinguish it from PID integration control.

Accumulator 490 includes adder 491 , delay element 492 and limiting operator 494 . The adder 491 adds the previous value Tb ^* _n-1 of the base assist command input via the delay element 492 to the current value of the torque TM to be processed. A limit calculator 494 limits the addition result of the adder 491 with a limit value that can be output as assist torque. This solves the windup problem, that is, the phenomenon in which the decrease in output is delayed when the sign of the deviation reverses after a value larger than the allowable output is taken by integration when the deviation continues to occur. ing.

The formula for servo control is shown below. The steering torque deviation ΔT is represented by Equation (1).
ΔT=Ts ^* -Ts (1)

Base assist command Tb ^* is represented by equation (2). In the configuration of FIG. 3, the proportional gain Kp, integral gain Ki, and differential gain Kd are all set to negative values.

The proportional component, the integral component, and the differential component added by the PID component adder 48 pass through the accumulation processing unit 490 to obtain each element of the PID control (proportional control torque, integral control torque, differential control The base assist command Tb ^* is calculated by being reflected in an amount corresponding to torque).

To discretize equation (2), substituting the bilinear transformation equation represented by equation (3) into equation (2) and arranging it gives equation (4). ts in Expression (3) indicates the calculation cycle. In FIG. 3, (ts/2)Ki is collectively written as "Ki".

Here, attention is focused on the phase relationship between the steering torque Ts and the amount corresponding to the differential control torque of the PID control obtained by the accumulation processing of the accumulation processing section 490 . In FIG. 3, the differential component itself output from the differential gain multiplier 57 is equivalent to a signal obtained by the second order differential control operation of the steering torque deviation .DELTA.T by the calculations of the delay element 55 and the subtractor 56. FIG. When this differential component passes through the accumulation processing unit 490, it becomes a differential control torque for PID control. The cumulatively processed differential control torque corresponds to "assist torque leading in phase with respect to steering torque". Therefore, the differential component, which is an element related to the differential control torque, corresponds to "an element related to the assist torque whose phase is advanced with respect to the steering torque".

It should be noted that the proportional component shown in FIG. 3 is a signal obtained by taking the difference from the previous value by calculation of the delay element 453 and the subtractor 463, so the phase is ahead of the steering torque. However, the amount corresponding to the proportional control torque of the PID control obtained by the accumulation processing of the accumulation processing unit 490 has the same phase as the steering torque, and does not correspond to "the assist torque whose phase is ahead of the steering torque". Therefore, the proportional component, which is an element related to the proportional control torque, does not correspond to "an element related to the assist torque whose phase leads the steering torque".

A detailed configuration of the differential component calculator 450 will be described with reference to FIG. First, the configuration relating to normal differential component calculation excluding reset processing will be described. The pseudo-differential calculation unit 50 has a delay element 51 and a subtractor 52 for inputting the steering torque deviation ΔT, and a multiplier 53 and a low-pass filter 54 provided on the output side of the subtractor 52 . A multiplier 53 multiplies the difference between the current value and the previous value of the steering torque deviation ΔT by the reciprocal (1/ts) of the calculation period ts, and outputs a differential differential of the steering torque deviation.

The low-pass filter 54 removes high frequency components from the input steering torque deviation differential, and outputs a steering torque differential differential D(ΔT). The RAM inside the low-pass filter 54 stores a plurality of previous values and, depending on the calculation configuration, a plurality of past values retroactively from the previous value, and a value filtered based on these past values is output.

The delay element 55, the subtractor 56, and the gain multiplier 57 for the steering torque deviation differential D(.DELTA.T) are as described above with reference to FIG. The output of the subtractor 56, that is, the difference between the current value and the previous value of the steering torque deviation differential D(ΔT) is referred to as the steering torque deviation differential. In the configuration example of the PID controller shown in FIGS. 3 and 4, the steering torque deviation differential difference is multiplied by the differential gain Kd. Note that the operation of the fourth term on the right side of Equation (4) may be realized by another configuration of the PID controller.

Next, as an additional configuration for reset processing, a switch 535 is provided on the input side of the pseudo-differential operation section 50 to the low-pass filter 54 . Although not shown, the low-pass filter 54 is provided with a switch for switching the input to be filtered and means for clearing the RAM value to zero. Further, a switch 555 is provided on the previous value input side of the steering torque deviation differential subtractor 56 . The steering torque saturation flag is input to these switch 535 , low-pass filter 54 and switch 555 .

The steering torque saturation determination unit 38 determines the absolute value of the steering torque |Ts| Determine if is saturated. When the steering torque saturation determination unit 38 determines that the steering torque absolute value |Ts| be done. Numbers <1> to <3> corresponding to the input locations of the steering torque saturation flag in FIG. Hereinafter, "0" in reset processing is not limited to strict 0, but is interpreted as including "a value close to 0" to the extent that it does not affect the calculation result of the differential component.

<1> The switch 535 of the pseudo differential operation unit 50 is switched to the "0" side, and 0 is input to the low-pass filter 54 instead of the original steering torque deviation differential differential. As a result, the current input to the low-pass filter 54 is 0.

<2> As an input to be processed by the low-pass filter 54, 0 is used instead of a plurality of past values. That is, filtering is performed using 0's. Alternatively, all past values stored in the RAM are cleared to 0. As a result, the current value D(ΔT) _n of the steering torque deviation differential output by the low-pass filter 54 becomes zero.

<3> The switch 555 on the previous value input side of the steering torque deviation differential subtractor 56 is switched to the "0" side. As a result, 0 is input to the subtractor 56 instead of the previous value D(ΔT) _n−1 of the original steering torque deviation output from the delay element 55 . As a result, the steering torque deviation differential difference input to the differential gain multiplier 57 becomes zero. Therefore, the differential component output from the differential component calculator 450 becomes 0, and the reset process is completed.

By the measures <1> to <3>, the differential component becomes 0 when the absolute value |Ts| of the steering torque reaches saturation, and a signal that continues from that state is obtained at the next calculation. <1> and <2> of <1> to <3>, that is, the input to the low-pass filter 54 in the differential component calculation and the action of resetting the past value stored in the low-pass filter 54 are all is required for On the other hand, the reset procedure of <3> may be omitted depending on the configuration of PID control.

Next, the technical significance of this embodiment will be described with reference to FIGS. 5 to 7. FIG. FIG. 5(a) shows the operation of the servo control calculation of the comparative example, and FIG. 5(b) shows the operation of the servo control calculation of the present embodiment. 6 and 7 show actual vehicle data for a comparative example and this embodiment, respectively. The computation of the comparative example corresponds to the normal servo control computation according to the prior art such as Patent Document 1. The servo output is the base assist command Tb ^* .

5(a) and 5(b) show waveforms of the steering torque Ts, the steering torque deviation differential D(ΔT), and the differential component. Since the value of the steering torque Ts is positive, the "absolute value" is omitted. The steering torque Ts increases, reaches saturation, and then decreases. The waveforms of the steering torque Ts and the steering torque deviation differential D(ΔT) are the same between the comparative example and the present embodiment, and the waveforms of the differential components are different.

The differential component is added to the proportional component, the integral component, and the previous servo output, resulting in a new limited servo output. In the comparative example, when the steering is sharp toward the end, the servo output increases or reaches the output upper limit until the time before the hatched portion (see actual vehicle data in FIG. 6). After that, when the steering torque Ts is saturated due to hitting the end, etc., a large differential component is generated on the negative side, which acts to lower the servo output.

In this embodiment, when the steering torque Ts is saturated such as when the steering wheel hits the end, the differential component becomes 0 by resetting the internal state of the low-pass filter 54 in the differential component calculation. At this time, the servo output is not affected by the differential component, and a decrease in the servo output is avoided (see actual vehicle data in FIG. 7).

6 and 7 show the steering angle, steering torque Ts, differential component, servo output, steering angular acceleration, and steering angular velocity in order from the top. A period of about 0.03 to 0.05 [sec] is the end contact stop section, and the steering torque Ts reaches saturation in the latter half of the end contact stop section. Here, since the value of the steering torque Ts is positive also in FIGS. 6 and 7, the "absolute value" is omitted. Also, the target steering torque Ts ^* is assumed to be constant.

In the comparative example shown in FIG. 6, as indicated by (*1), when the steering torque Ts is saturated, a sharp differential component is generated in the direction of pushing back the steering wheel. Along with this, as indicated by (*2), the differential component lowers the servo output. For example, it rapidly decreases from approximately 100 [Nm] to approximately 50 [Nm].

Also, as indicated by (*3), the steering angular velocity changes from positive to a negative value (approximately -100 [deg/s]) beyond 0 after passing through the end contact stop section. In other words, a behavior in which the steering wheel bounces back occurs.

In this embodiment shown in FIG. 7, the differential component calculation is reset when the steering torque Ts is saturated. As shown, the servo output is constant and does not drop when the end is hit. Also, as indicated by (*6), the steering angular velocity is maintained at approximately 0 after passing the end contact stop section, and the behavior of the steering wheel being bounced back is eliminated.

It should be noted that the change in the differential component and the servo output at around 0.08 [sec] is due to the intentional return operation of the driver, and is not a problem.

As described above, in this embodiment, when the steering torque Ts is saturated, the servo controller 400 resets the differential component calculation of the PID control, so that torque in the direction of pushing back the steering wheel is not generated and the steering wheel is not pushed back. Be able to steer. Therefore, even if it saturates with sudden steering, it is eliminated that it becomes heavy for a moment. Also, when it hits the end, the handle will stop at that position without being bounced back.

(Other embodiments)
(a) The servo controller 400 is not limited to performing PID control, but may use a transfer function to calculate the base assist command Tb ^* so that the steering torque Ts follows the target steering torque Ts ^* . In this configuration, the servo controller 400 resets the calculation of "the element related to the assist torque whose phase is advanced with respect to the steering torque" instead of the calculation of the differential component of the PID control. As a result, as in the above embodiment, it is possible to prevent the steering wheel from being pushed back when the absolute value of the steering torque is saturated.

(b) The estimated load torque calculation unit 20 calculates the estimated load torque Tx based on the steering torque Ts instead of the target steering torque Ts ^* and based on the assist torque Ta instead of the base assist command Tb ^* . good too.

(c) The steering control device of the present invention is not limited to an electric power steering system, and as disclosed in FIG. Apparatus may be applied. In this case, in the servo controller, the steering torque Ts detected by the reaction force detection device follows the target steering torque Ts ^* calculated according to the load and steering angle calculated by the tire steering device. controlled.

The present invention is not limited to such embodiments, and can be embodied in various forms without departing from the scope of the invention.

10 ... ECU (steering control device),
38 ... steering torque saturation determination section,
400 Servo controller,
80... Motor.

Claims (3)

a servo controller (400) that calculates an output command (Tb ^* ) for a motor (80) so that the steering torque (Ts) follows the target steering torque (Ts ^* );
a steering torque saturation determination section (38) that determines that the absolute value of the steering torque is saturated;
with
When the steering torque saturation determination section determines that the absolute value of the steering torque is saturated, the servo controller resets the calculation of the elements related to the assist torque whose phase is advanced with respect to the steering torque. Control device. The servo controller performs PID control,
2. The steering control device according to claim 1, wherein when the steering torque saturation determining section determines that the absolute value of the steering torque is saturated, the servo controller resets the differential component calculation of the PID control. When the steering torque saturation determination section determines that the absolute value of the steering torque is saturated, the servo controller at least controls the input to the low-pass filter (54) in differential component calculation and the low-pass filter 3. A steering control system as claimed in claim 2, resetting the past value stored in the .

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