Steering system, control method

Abstract

The present invention provides a steering device that makes it easier to return the steering wheel to the neutral position when turning back, while preventing a deterioration in steering feel. [Solution] A steering device comprising a motor that provides a driving force to assist steering to the steering wheel, and a control device that controls the motor's drive using a basic current calculated based on at least the steering torque or steering angle, wherein the control device sets a target steering angular velocity, which is a target value of the steering angular velocity, using the vehicle speed and the steering angle, calculates the actual steering angular velocity, which is the actual speed of the steering angle, sets a correction base current corresponding to the steering angular velocity difference, which is the difference between the target steering angular velocity and the actual steering angular velocity, sets a correction coefficient corresponding to the steering state grasped using the actual steering angular velocity, sets a correction current using the correction base current and the correction coefficient, and sets the value obtained by adding the correction current to the basic current as the target current.

Description

Technical Field

[0001] The present invention relates to a steering device and a control method.

Background Art

[0002] For example, the device described in Patent Document 1 is an electric power steering device that includes steering assist control means for calculating an assist base current value based on steering torque and vehicle speed, where an assist motor is drive-controlled in accordance with an assist target current based on the assist base current value to assist human power. Further, the device described in Patent Document 1 includes steering angle detection means for detecting a steering angle, and reaction force current adding means for calculating a reaction force current value that applies a return reaction force in the steering angle neutral direction at a small steering angle based on the vehicle speed and the steering angle, and adding the reaction force current value to the assist base current value. Further, the device described in Patent Document 1 includes hands-off determination means for determining whether or not the steering wheel is in a hands-off state based on the steering torque, steering wheel return correction current value calculation means for calculating a steering wheel return correction current value based on the steering angle, the vehicle speed and the steering torque when the hands-off determination means determines that the steering wheel is in the hands-off state, and steering wheel return control means for adding the steering wheel return correction current value calculated by the steering wheel return correction current value calculation means to the assist base current value only when the determination result of the hands-off determination means is that the steering wheel is in the hands-off state. In the device described in Patent Document 1, a deviation of the final target steering angular velocity from the actual steering angular velocity is obtained, and the deviation is converted into a current by current conversion means to obtain the steering wheel return correction current value. This current conversion is calculated by multiplying the deviation by a predetermined conversion coefficient, and is output to the steering wheel return control means. The steering wheel return control means receives and processes the determination result signal from the hands-off determination means and the steering wheel return correction current value as the calculation result from the steering wheel return correction current value calculation means, and outputs a final steering wheel return correction current value. The final steering wheel return correction current value is added to the assist base current calculated by the steering assist control means, so that the assist base current is corrected.

Prior Art Documents

Patent Documents

[0003] [Patent Document 1] Japanese Patent Publication No. 2007-296900 [Overview of the project] [Problems that the invention aims to solve]

[0004] In situations where the steering wheel (or "handle" in Patent Document 1) is turned in and then returned to its original position, it is desirable to increase the amount of motor assistance to facilitate the return of the handle to the neutral position during the return. For example, in the device described in Patent Document 1, it is desirable to increase the handle return correction current value added to the assist base current during the return. Furthermore, when increasing the amount of assistance to facilitate the return of the steering wheel to the neutral position during the return, it is desirable to consider the steering conditions so as not to worsen the steering feel. The present invention aims to provide a steering device that makes it easier to return the steering wheel to the neutral position when turning back, without degrading the steering feel. [Means for solving the problem]

[0005] To this end, the present invention provides a steering device comprising: a motor that provides a driving force to assist steering to the steering wheel; and a control device that controls the drive of the motor using a basic current calculated based on at least the steering torque or steering angle, wherein the control device sets a target steering angular velocity, which is a target value of the steering angular velocity, using the vehicle speed and the steering angle; calculates the actual steering angular velocity, which is the actual speed of the steering angle; sets a correction base current corresponding to the steering angular velocity difference, which is the difference between the target steering angular velocity and the actual steering angular velocity; sets a correction coefficient corresponding to the steering state grasped using the actual steering angular velocity; sets a correction current using the correction base current and the correction coefficient; and sets the value obtained by adding the correction current to the basic current as the target current. [Effects of the Invention]

[0006] According to the present invention, it is possible to make it easier to return the steering wheel to the neutral position when turning back, without degrading the steering feel. [Brief explanation of the drawing]

[0007] [Figure 1] This figure shows an example of a schematic configuration of an electric power steering system according to an embodiment. [Figure 2] This figure shows an example of a schematic configuration of a control device. [Figure 3] This figure shows an example of the schematic configuration of the target current setting unit. [Figure 4] This figure shows an example of a schematic configuration of the return current setting unit. [Figure 5] This figure shows an example of a schematic configuration of a control map that illustrates the correspondence between steering angle, vehicle speed, and target steering angular velocity. [Figure 6] This figure shows an example of a control map that illustrates the correspondence between actual steering angular velocity and correction coefficients. [Figure 7] This figure shows an example of changes in actual steering angular velocity, correction coefficient, and return current. [Figure 8] This figure shows an example of a control map that illustrates the correspondence between steering wheel input and output and correction coefficients. [Figure 9] This figure shows an example of changes in actual steering angular velocity, correction coefficient, and return current. [Modes for carrying out the invention]

[0008] Embodiments of the present invention will be described in detail below with reference to the attached drawings. Figure 1 is a diagram showing an example of a schematic configuration of an electric power steering device 100 according to an embodiment. Figure 2 shows an example of the schematic configuration of the control device 10. The electric power steering system 100 (hereinafter sometimes simply referred to as "steering system 100") is a steering device for arbitrarily changing the direction of travel of the vehicle 1. The vehicle 1 can be exemplified as an automobile.

[0009] The steering device 100 includes a steering wheel 101 operated by the driver to change the direction of travel of the vehicle 1, and a steering shaft 102 integrally provided with the steering wheel (in other words, the handle) 101. The steering device 100 also includes a first connecting shaft 103 connected to the steering shaft 102 via a universal joint 103a, and a second connecting shaft 104 connected to the first connecting shaft 103 via a universal joint 103b. The second connecting shaft 104 rotates in conjunction with the rotation of the steering wheel 101.

[0010] The steering device 100 also includes tie rods 105 connected to each of the left and right wheels (for example, front wheels) 150, which act as rolling wheels, and a rack shaft 106 connected to the tie rods 105. The steering device 100 also includes a pinion 107a that, together with the rack teeth 106a formed on the rack shaft 106, constitutes a rack and pinion mechanism. The pinion 107a is formed at the lower end of the pinion shaft 107. The pinion shaft 107 rotates on the rack shaft 106, which drives the wheels 150, and applies a driving force that causes the wheels 150 to roll.

[0011] Furthermore, the steering device 100 has a steering gearbox 130 that houses the pinion shaft 107. The pinion shaft 107 is connected to the second connecting shaft 104 via a torsion bar 108 within the steering gearbox 130. Inside the steering gearbox 130, there is a torque sensor 109 that can detect the steering torque applied to the steering wheel 101 based on the relative rotation angle between the second connecting shaft 104 and the pinion shaft 107. For example, the torque sensor 109 can be described as a sensor that can detect the steering torque based on the amount of twist of the torsion bar 108.

[0012] Furthermore, the steering device 100 includes a motor 110 supported by a steering gearbox 130 and a reduction mechanism 111 that reduces the driving force of the motor 110 and transmits it to the pinion shaft 107. The reduction mechanism 111 consists of, for example, a worm wheel (not shown) fixed to the pinion shaft 107 and a worm gear (not shown) fixed to the output shaft of the motor 110. The motor 110 applies a driving force to the rack shaft 106 to roll the wheels 150 by applying a rotational driving force to the pinion shaft 107. For example, the motor 110 can be a three-phase brushless motor having a resolver 120 that outputs a rotation angle signal θms linked to the motor rotation angle θm, which is the rotation angle of the motor 110.

[0013] Furthermore, the steering device 100 includes a control device 10 that controls the operation of the motor 110. The control device 10 receives the output signal from the torque sensor 109 mentioned above. The control device 10 also receives the output signal from the vehicle speed sensor 170, which detects the vehicle speed Vc, the moving speed of the vehicle 1, via a communication network (in other words, CAN) that transmits signals for controlling various devices mounted on the vehicle 1.

[0014] The steering device 100 configured as described above drives the motor 110 based on the steering torque T detected by the torque sensor 109, and transmits the torque generated by the motor 110 to the pinion shaft 107. Thereby, the torque generated by the motor 110 assists the driver's steering force applied to the steering wheel 101.

[0015] Next, the control device 10 will be described. The control device 10 is an arithmetic logic circuit including a CPU (Central Processing Unit) (not shown), a ROM (Read Only Memory) (not shown), a RAM (Random Access Memory) (not shown), a backup RAM (not shown), and the like. To the control device 10, a torque signal Td obtained by converting the steering torque T detected by the above-described torque sensor 109 into an output signal, a vehicle speed signal v obtained by converting the vehicle speed Vc detected by the vehicle speed sensor 170 into an output signal, a rotation angle signal θms from the resolver 120, and the like are input.

[0016] The control device 10 includes a target current setting unit 20 that sets a target current It to be supplied to the motor 110 based on the torque signal Td, the vehicle speed signal v, the rotation angle signal θms, and the like. The control device 10 also includes a drive control unit 30 that performs feedback control and the like based on the target current It set by the target current setting unit 20. The control device 10 further includes a motor rotation angle calculation unit 71 that calculates a motor rotation angle θm of the electric motor 110, and a motor rotation speed calculation unit 72 that calculates a motor rotation speed Vm based on the motor rotation angle θm calculated by the motor rotation angle calculation unit 71. The control device 10 further includes a steering angle calculation unit 73 that calculates a steering angle θs which is the rotation angle of the steering wheel 101, and a steering angular velocity calculation unit 74 that calculates an actual steering angular velocity ωa based on the steering angle θs calculated by the steering angle calculation unit 73.

[0017] (Drive Control Unit 30) The drive control unit 30 includes a motor drive control unit (not shown) that controls the operation of the motor 110, a motor drive unit (not shown) that drives the motor 110, and a motor current detection unit (not shown) that detects the actual current flowing through the motor 110. The motor drive control unit includes a feedback control unit (not shown) that performs feedback processing so that the difference between the target current It set in the target current setting unit 20 and the actual current supplied to the motor 110 detected by the motor current detection unit becomes zero. The motor drive control unit also includes a PWM signal generation unit (not shown) that generates a PWM signal for driving the motor 110 using PWM. The motor drive unit is a so-called inverter, and for example, it is equipped with six independent transistors (FETs) as switching elements. The motor current detection unit detects the value of the actual current flowing to the motor 110 from the voltage generated across the shunt resistor connected to the motor drive unit.

[0018] The motor rotation angle calculation unit 71 calculates the motor rotation angle θm based on the rotation angle signal θms from the resolver 120. The motor rotation speed calculation unit 72 calculates the motor rotation speed Vm of the electric motor 110 based on the motor rotation angle θm calculated by the motor rotation angle calculation unit 71.

[0019] The steering angle calculation unit 73 calculates the steering angle θs based on the motor rotation angle θm calculated by the motor rotation angle calculation unit 71. This is because the steering wheel 101, the reduction mechanism 111, etc. are mechanically connected, so there is a correlation between the rotation angle of the steering wheel 101 (in other words, the steering angle θs) and the motor rotation angle θm of the electric motor 110. The steering angle calculation unit 73 then calculates the steering angle θs based on the cumulative difference between the previous value and the current value of the motor rotation angle θm, which is periodically (for example, every 1 millisecond) calculated by the motor rotation angle calculation unit 71. The steering device 100 may also be equipped with a steering angle sensor that detects the rotation angle of the steering wheel 101, and the steering angle calculation unit 73 may calculate the steering angle θs based on the signal obtained from the steering angle sensor. The steering angular velocity calculation unit 74 calculates the actual steering angular velocity ωa, which is the angle by which the steering wheel 101 rotates in a unit time, based on the steering angle θs calculated by the steering angle calculation unit 73.

[0020] Next, the target current setting unit 20 will be described in detail. Figure 3 shows an example of the schematic configuration of the target current setting unit 20. The target current setting unit 20 includes a first setting unit 21 for setting a base current Ib, which serves as the basis for setting the target current It, and a second setting unit 22 for setting an inertia compensation current Is to cancel out the moment of inertia of the motor 110. The target current setting unit 20 also includes a third setting unit 23 for setting a damper compensation current Id that limits the rotation of the motor 110. The target current setting unit 20 also includes a provisional determination unit 25 that determines a provisional target current Itf, which is a provisional target current, based on the values ​​set in the first setting unit 21, the second setting unit 22, and the third setting unit 23. The target current setting unit 20 also includes a phase compensation unit 26 that compensates for the phase of the steering torque T detected by the torque sensor 109.

[0021] Furthermore, the target current setting unit 20 includes a return current setting unit 40 that sets a return current Ir, which is a correction current for returning the steering wheel 101 to the neutral position. The target current setting unit 20 also includes a final determination unit 28 that determines the final target current It based on the provisional target current Itf determined by the provisional determination unit 25 and the return current Ir set by the return current setting unit 40.

[0022] The first setting unit 21 sets the base current Ib based on the torque signal Ts obtained by phase compensation of the torque signal Td in the phase compensation unit 26, the vehicle speed signal v from the vehicle speed sensor 170, and a pre-created control map. In other words, the first setting unit 21 sets the base current Ib according to the steering torque T and the vehicle speed Vc. The second setting unit 22 sets an inertia compensation current Is to cancel out the moment of inertia of the motor 110 and the system based on the torque signal Ts and the vehicle speed signal v. In other words, the second setting unit 22 sets an inertia compensation current Is in accordance with the steering torque T and the vehicle speed Vc. The third setting unit 23 sets a damper compensation current Id that limits the rotation of the motor 110 based on the torque signal Ts, the vehicle speed signal v, and the output signal from the motor rotation speed calculation unit 72. In other words, the third setting unit 23 sets a damper compensation current Id corresponding to the steering torque T, the vehicle speed Vc, and the motor rotation speed Vm.

[0023] Here, the neutral state is defined as the state where the twist amount of the torsion bar 108 is 0, and the direction in which the relative rotation angle between the second connecting shaft 104 and the pinion shaft 107 changes when the steering wheel 101 rotates to the right from the neutral state is defined as positive. When the steering wheel 101 rotates to the right, the steering torque T detected by the torque sensor 109 is positive. Also, the direction in which the relative rotation angle between the second connecting shaft 104 and the pinion shaft 107 changes when the steering wheel 101 rotates to the left from the neutral state is defined as negative. When the steering wheel 101 rotates to the left, the steering torque T detected by the torque sensor 109 is negative. When the steering torque T detected by the torque sensor 109 is positive, the base current Ib is set in the first setting unit 21 to rotate the electric motor 110 in the rightward direction, and the direction in which this base current Ib flows is defined as positive. In other words, when the steering torque T is positive, the first setting unit 21 calculates a positive base current Ib and generates torque in the direction that rotates the electric motor 110 to the right. When the steering torque T is negative, the first setting unit 21 calculates a negative base current Ib and generates torque in the direction that rotates the electric motor 110 to the left. Furthermore, when the steering wheel 101 rotates to the right from 0 degrees (in other words, the neutral position), the steering angle θs calculated by the steering angle calculation unit 73 is positive. On the other hand, when the steering wheel 101 rotates to the left from 0 degrees, the steering angle θs calculated by the steering angle calculation unit 73 is negative.

[0024] The provisional determination unit 25 determines the provisional target current Itf based on the base current Ib set in the first setting unit 21, the inertia compensation current Is set in the second setting unit 22, and the damper compensation current Id set in the third setting unit 23. For example, the provisional determination unit 25 determines the provisional target current Itf as a value obtained by adding the inertia compensation current Is and subtracting the damper compensation current Id from the base current Ib.

[0025] The final determination unit 28 determines the final target current It based on the provisional target current Itf determined by the provisional determination unit 25 and the return current Ir set by the return current setting unit 40. In this embodiment, the final determination unit 28 determines the target current It as the value obtained by adding the return current Ir set by the return current setting unit 40 to the provisional target current Itf determined by the provisional determination unit 25.

[0026] Next, the return current setting unit 40 will be described in detail. Figure 4 shows an example of the schematic configuration of the return current setting unit 40. The return current setting unit 40 sets the return current Ir, which is a correction current for returning the steering wheel to the neutral position. The return current setting unit 40 includes a target setting unit 41 for setting a target steering angular velocity ωt, and a difference calculation unit 42 for calculating the steering angular velocity difference Δω, which is the difference between the target steering angular velocity ωt set by the target setting unit 41 and the actual steering angular velocity ωa. The return current setting unit 40 also includes a base setting unit 43 for setting the return base current Irb based on the steering angular velocity difference Δω calculated by the difference calculation unit 42. The return current setting unit 40 also includes a steering state recognition unit 44 for recognizing the steering state, and a correction coefficient setting unit 45 for setting a correction coefficient K based on the steering state recognized by the steering state recognition unit 44. The return current setting unit 40 also includes a multiplication unit 46 for multiplying the return base current Irb set by the base setting unit 43 by the correction coefficient K set by the correction coefficient setting unit 45. The return current setting unit 40 then sets the value obtained by the multiplication unit 46 multiplying the return base current Irb by the correction coefficient K as the return current Ir.

[0027] Figure 5 shows a schematic example of a control map that illustrates the correspondence between steering angle θs, vehicle speed Vc, and target steering angular velocity ωt. The target setting unit 41 sets the target steering angular velocity ωt based on the steering angle θs and the vehicle speed Vc. The target setting unit 41 calculates the target steering angular velocity ωt based on the output signal from the steering angle calculation unit 73 and the output signal from the vehicle speed sensor 170, using a control map, for example, shown in Figure 5, which has been created in advance and stored in a memory unit (for example, ROM). In other words, the target setting unit 41 sets the target steering angular velocity ωt according to the steering angle θs and the vehicle speed Vc. In the control map shown in Figure 5, the horizontal axis is the steering angle θs and the vertical axis is the target steering angular velocity ωt. On the horizontal axis, the origin is the neutral position of the steering angle θs, the area to the right of the origin is the position when the steering wheel 101 is rotating to the right, and the area to the left of the origin is the position when the steering wheel 101 is rotating to the left. On the vertical axis, the origin is the target steering angular velocity ωt = 0, the area above the origin is the direction of rotation of the steering wheel 101 to the right, and the area below the origin is the direction of rotation of the steering wheel 101 to the left.

[0028] In the control map illustrated in Figure 5, the relationship between the steering angle θs and the target steering angular velocity ωt is represented by a smooth curve symmetrically with respect to the origin in the second and fourth quadrants. More specifically, as the steering angle θs increases from 0 (in other words, as it increases in the clockwise direction), the target steering angular velocity ωt increases in the negative direction (in other words, as it increases in the counterclockwise direction). Also, at the beginning of the steering angle θs increasing from 0, in other words, when the steering angle θs is small, the absolute value of the target steering angular velocity ωt increases rapidly. On the other hand, as the steering angle θs increases, the rate at which the absolute value of the target steering angular velocity ωt increases gradually decreases. Conversely, as the steering angle θs decreases from 0 (in other words, as it increases in the counterclockwise direction), the target steering angular velocity ωt increases in the positive direction (in other words, as it increases in the clockwise direction). Also, at the beginning of the steering angle θs decreasing from 0, in other words, when the absolute value of the actual steering angle θs is small, the absolute value of the target steering angular velocity ωt increases rapidly. On the other hand, as the steering angle θs decreases, the rate at which the absolute value of the target steering angular velocity ωt increases gradually decreases. Furthermore, in the control map illustrated in Figure 5, when the absolute value of the steering angle θs is the same, the absolute value of the target steering angular velocity ωt increases as the vehicle speed Vc increases.

[0029] The difference calculation unit 42 calculates the steering angular velocity difference Δω by subtracting the actual steering angular velocity ωa calculated by the steering angular velocity calculation unit 74 from the target steering angular velocity ωt set by the target setting unit 41 (Δω = ωt - ωa). The base setting unit 43 calculates the return base current Irb by multiplying the steering angular velocity difference Δω calculated by the difference calculation unit 42 by a predetermined coefficient α (Irb = Δω × α).

[0030] The steering state sensing unit 44 determines whether the steering wheel 101 is turned in or out based on the steering angle θs calculated by the steering angle calculation unit 73 and the actual steering angular velocity ωa calculated by the steering angular velocity calculation unit 74. For example, the steering state sensing unit 44 determines that the steering wheel is turned in if the multiplicative value (=θs × ωa) obtained by multiplying the steering angle θs calculated by the steering angle calculation unit 73 and the actual steering angular velocity ωa calculated by the steering angular velocity calculation unit 74 is 0 or greater. On the other hand, the steering state sensing unit 44 determines that the steering wheel is out if the multiplicative value is less than 0. In other words, the steering state sensing unit 44 determines that the steering wheel 101 is turned in if the direction of the steering angle θs calculated by the steering angle calculation unit 73 and the direction of the actual steering angular velocity ωa calculated by the steering angular velocity calculation unit 74 are the same. On the other hand, the steering state recognition unit 44 determines that the steering is being reversed if the direction of the steering angle θs is different from the direction of the actual steering angular velocity ωa.

[0031] The correction coefficient setting unit 45 sets the correction coefficient K based on the determination result of whether the steering state is turned in or out, determined by the steering state understanding unit 44, and the actual steering angular velocity ωa. Figure 6 shows an example of a control map that illustrates the correspondence between the actual steering angular velocity ωa and the correction coefficient K. The correction coefficient setting unit 45 calculates the correction coefficient K from the control map illustrated in Figure 6. In the control map illustrated in Figure 6, the horizontal axis represents the absolute value of the actual steering angular velocity ωa and the vertical axis represents the correction coefficient K. The correction coefficient K is composed of a correction coefficient Kg when the steering wheel 101 is turned in and a correction coefficient Kr when it is turned out, and the correction coefficient Kg and the correction coefficient Kr are set to be different.

[0032] As shown in Figure 6, the correction coefficient Kg gradually decreases as the absolute value of the actual steering angular velocity ωa increases from 0, and when the absolute value of the actual steering angular velocity ωa is greater than or equal to a predetermined predetermined steering inward speed ωg, the correction coefficient Kg becomes a predetermined first predetermined value. On the other hand, the correction coefficient Kr gradually increases as the absolute value of the actual steering angular velocity ωa increases from 0, and when the absolute value of the actual steering angular velocity ωa is greater than or equal to a predetermined predetermined steering outward speed ωr, the correction coefficient Kr becomes a predetermined second predetermined value. Note that the predetermined steering inward speed ωg and the predetermined steering outward speed ωr may be the same or different.

[0033] Furthermore, when the absolute value of the actual steering angular velocity ωa is the same, the correction coefficient Kr is greater than the correction coefficient Kg. The difference between the correction coefficient Kr and the correction coefficient Kg gradually decreases as the absolute value of the actual steering angular velocity ωa approaches 0. When the absolute value of the actual steering angular velocity ωa is 0, the correction coefficient Kr and the correction coefficient Kg are the same and become the third predetermined value.

[0034] The operation of the steering device 100 will be described below. Figure 7 shows an example of the changes in actual steering angular velocity ωa, correction coefficient K, and return current Ir. Figure 7 shows an example of a driver making a left turn, specifically an example where the driver turns the steering wheel 101 from the neutral position to the left and then turns it back. When switching from steering inward to steering outward, the absolute value of the actual steering angular velocity ωa gradually decreases to zero. Therefore, according to the control map illustrated in Figure 6, the correction coefficient Kg, which is set as the correction coefficient K, gradually increases from the first predetermined value to the third predetermined value. Also, after switching to steering outward, the absolute value of the actual steering angular velocity ωa gradually increases from zero. Therefore, according to the control map illustrated in Figure 6, the correction coefficient Kr, which is set as the correction coefficient K, gradually increases from the third predetermined value to the second predetermined value. In other words, the correction coefficient K gradually increases immediately before switching from steering inward to steering outward, and immediately after switching to steering outward. As a result, the return current Ir also gradually increases immediately before switching from steering inward to steering outward, and immediately after switching to steering outward.

[0035] Figure 8 shows an example of a control map that illustrates the correspondence between the steering wheel 101's inward and outward movements and the correction coefficient K. Here, as a modified example of a return current setting unit (not shown), we consider a configuration in which the control map used by the correction coefficient setting unit 45 is different from that used by the return current setting unit 40. In other words, the modified example of a correction coefficient setting unit (not shown) sets the correction coefficient K2 using the control map in Figure 8 instead of the control map exemplified in Figure 6. In the control map exemplified in Figure 8, the correction coefficient K2 is composed of a correction coefficient K2g when the steering wheel 101 is turned in and a correction coefficient K2r when it is turned out, and the correction coefficients K2g and K2r are set to be different. The correction coefficients K2g and K2r are predetermined values, and the correction coefficient K2r is a larger value than the correction coefficient K2g.

[0036] Figure 9 shows an example of the changes in actual steering angular velocity ωa, correction coefficient K2, and return current Ir. Figure 9 shows an example of a driver making a left turn, specifically an example where the driver turns the steering wheel 101 from the neutral position to the left and then returns to the neutral position. In the modified return current setting section (not shown), a predetermined correction coefficient K2g is set when cutting, and a predetermined correction coefficient K2r is set when uncutting. Therefore, when switching from cutting to uncutting, the correction coefficient K2g switches to a correction coefficient K2r, which is a different value from the correction coefficient K2g. As a result, the return current Ir switches abruptly when switching from cutting to uncutting.

[0037] As explained with reference to Figures 7 and 9, in the steering device 100 having a return current setting unit 40, the change in the return current Ir when switching from steering inward to steering outward is smaller than in the case of having a modified return current setting unit (not shown). Therefore, with the steering device 100 having a return current setting unit 40, the steering feel does not deteriorate due to the application of the return current Ir.

[0038] Furthermore, when switching from steering inward to steering outward, the judgment result of the steering state recognition unit 44 may alternate between steering inward and steering outward due to external influences such as the road surface. In the modified return current setting unit (not shown), when the judgment result alternates, the correction coefficient K2 also alternates between correction coefficient K2g and correction coefficient K2r. Therefore, if the difference between correction coefficient K2g and correction coefficient K2r is large, the change in the return current Ir becomes drastic. On the other hand, in the return current setting unit 40, even if the judgment result alternates and the correction coefficient K alternates between correction coefficient Kg and correction coefficient Kr, the difference between correction coefficient Kg and correction coefficient Kr is small, so the change in the return current Ir is also small. Therefore, with the steering device 100 having the return current setting unit 40, the steering feeling can be prevented from deteriorating due to the application of the return current Ir, more so than in the case of having the modified return current setting unit (not shown).

[0039] Furthermore, in order to suppress the judgment result of the steering state sensing unit 44 from switching alternately between steering inward and steering outward due to external influences such as the road surface, it is conceivable to provide a filter (for example, a low-pass filter) upstream of the steering state sensing unit 44. However, providing a filter may cause a phase delay in the return current Ir. Therefore, the steering device 100 having a return current setting unit 40 can provide a more accurate return current Ir setting compared to a configuration with a filter, and it is possible to prevent deterioration of the steering feel due to the application of the return current Ir.

[0040] Furthermore, in the steering device 100, when the steering wheel 101 is turned back, a return current Ir corresponding to the correction coefficient Kr is set, making it easier for the steering wheel 101 to return to the neutral position. Therefore, the steering load on the driver can be reduced. Also, when the steering wheel 101 is turned inward, a return current Ir corresponding to the correction coefficient Kg is set, making it easier for the driver to understand the neutral position.

[0041] The steering device 100 described above includes a motor 110 that provides a driving force to assist steering the steering wheel 101, and a control device 10 that controls the drive of the motor 110 using a provisional target current Itf (an example of a basic current) calculated based on the steering torque T. The control device 10 calculates the actual steering angular velocity ωa, which is the actual speed at the steering angle θs, and sets the target steering angular velocity ωt, which is the target value of the steering angular velocity, using the vehicle speed Vc and the steering angle θs. The control device 10 then sets a return base current Irb (an example of a correction base current) according to the steering angular velocity difference Δω, which is the difference between the target steering angular velocity ωt and the actual steering angular velocity ωa, and sets a correction coefficient K according to the steering state grasped using the actual steering angular velocity ωa. The control device 10 then sets a return current Ir (an example of a correction current) using the return base current Irb and the correction coefficient K, and sets the value obtained by adding the return current Ir to the provisional target current Itf as the target current It.

[0042] With the steering device 100 configured as described above, the value obtained by adding the return current Ir to the provisional target current Itf is set as the target current It, making it easier to return the steering wheel 101 to the neutral position when turning back. Furthermore, with the steering device 100, the return current Ir can be set using a correction coefficient K according to the steering state, so the steering feel can be prevented from deteriorating by adjusting the correction coefficient K.

[0043] The control device 10 is set so that the correction coefficient K is different depending on whether the steering wheel 101 is turned in or out of the steering position. This allows the return current Ir to be changed depending on whether the steering wheel 101 is turned in or out of the steering position, thereby adjusting the steering feel given to the driver according to the steering state.

[0044] For example, the control device 10 is set so that the correction coefficient Kr when the steering wheel is turned back is greater than the correction coefficient Kg when the steering wheel is turned inward. This reduces the steering load on the driver when the steering wheel is turned back, and when the steering wheel is turned inward, it is possible to set a return current Ir that is sufficient to make the neutral position easily understandable to the driver.

[0045] Furthermore, the control device 10 is set so that the correction coefficient Kr when the steering is reversed gradually increases as the absolute value of the actual steering angular velocity ωa increases from 0. This allows the return current Ir to be gradually increased after switching from steering in to reverse, thereby suppressing deterioration of the steering feel caused by the addition of the return current Ir.

[0046] Furthermore, the control device 10 is set so that the correction coefficient Kg when the steering wheel is turned in gradually decreases as the absolute value of the actual steering angular velocity ωa increases from 0. In other words, the control device 10 is set so that the correction coefficient Kg when the steering wheel is turned in gradually increases as the absolute value of the actual steering angular velocity ωa approaches 0. This allows the return current Ir to be gradually increased just before switching from turned in to unturned, thereby suppressing deterioration of the steering feel caused by the addition of the return current Ir.

[0047] Furthermore, the control device 10 is set so that the difference between the correction coefficient Kr when the steering is unscrewed and the correction coefficient Kg when the steering is turned in gradually decreases as the absolute value of the actual steering angular velocity ωa approaches 0. This allows the return current Ir to be gradually increased just before switching from turned in to unscrewed and after switching to unscrewed, thereby suppressing deterioration of the steering feel.

[0048] Furthermore, the control device 10 is set so that the correction coefficient Kr when the steering is unscrewed and the correction coefficient Kg when the steering is turned in are the same when the absolute value of the actual steering angular velocity ωa is 0. This prevents deterioration of the steering feel because the return current Ir does not change significantly when switching from turned in to unscrewed.

[0049] In the target current setting unit 20 described above, the provisional target current Itf, to which the return current Ir is added, is set using the steering torque T. For example, the first setting unit 21 sets a base current Ib according to the steering torque T and the vehicle speed Vc. However, the provisional target current Itf to which the return current Ir is added may be set using the steering angle θs instead of the steering torque T. Alternatively, the provisional target current Itf to which the return current Ir is added may be set using the steering angle θs in addition to the steering torque T, or it may be set using the actual steering angular velocity ωa.

[0050] The control method used by the control device 10 to control the drive of the motor 110 involves setting a target steering angular velocity ωt, which is the target value of the steering angular velocity, using the vehicle speed Vc and the steering angle θs, and calculating the actual steering angular velocity ωa, which is the actual speed of the steering angle θs. The control method then sets a return base current Irb according to the steering angular velocity difference Δω, which is the difference between the target steering angular velocity ωt and the actual steering angular velocity ωa, and sets a correction coefficient K according to the steering state determined using the actual steering angular velocity ωa. The control method then sets a return current Ir using the return base current Irb and the correction coefficient K, and sets the current value obtained by adding the return current Ir to the provisional target current Itf as the target current It.

[0051] According to the above control method, the value obtained by adding the return current Ir to the provisional target current Itf is set as the target current It, making it easier to return the steering wheel 101 to the neutral position when turning back. Furthermore, according to the above control method, the return current Ir can be set using a correction coefficient K according to the steering state, so the steering feel can be prevented from deteriorating by adjusting the correction coefficient K. [Explanation of symbols]

[0052] 10...Control device, 20...Target current setting unit, 40...Return current setting unit, 100...Steering device, 101...Steering wheel, 110...Motor

Claims

1. A motor that provides driving force to assist steering the steering wheel, A control device that controls the drive of the motor using a basic current calculated based on at least the steering torque or steering angle, Equipped with, The control device sets a target steering angular velocity, which is a target value of the steering angular velocity, using the vehicle speed and the steering angle; calculates the actual steering angular velocity, which is the actual speed of the steering angle; sets a correction base current according to the steering angular velocity difference, which is the difference between the target steering angular velocity and the actual steering angular velocity; sets a correction coefficient according to the steering state grasped using the actual steering angular velocity; sets a correction current using the correction base current and the correction coefficient; and sets the value obtained by adding the correction current to the basic current as the target current. Steering system.

2. The control device is configured such that the correction coefficient differs depending on whether the steering wheel is turned in or out of the turn. The steering device according to claim 1.

3. The control device is set such that the correction coefficient when the cut-back is greater than the correction coefficient when the cut-in is greater. The steering device according to claim 2.

4. The control device is configured such that the correction coefficient when the steering is reversed gradually increases as the absolute value of the actual steering angular velocity increases from 0. The steering device according to claim 2.

5. The control device is configured such that the correction coefficient when the steering is turned in gradually decreases as the absolute value of the actual steering angular velocity increases from 0. The steering device according to claim 2.

6. The control device is configured such that the difference between the correction coefficient when the steering is reversed and the correction coefficient when the steering is turned in gradually decreases as the absolute value of the actual steering angular velocity approaches zero. The steering device according to claim 2.

7. The control device is set such that the correction coefficient when the steering is reversed and the correction coefficient when the steering is turned in are the same when the absolute value of the actual steering angular velocity is 0. The steering device according to claim 6.

8. A control method for controlling the drive of a motor that provides a driving force to assist steering to the steering wheel, using a basic current calculated based on at least the steering torque or steering angle, A target steering angular velocity is set using the vehicle speed and the steering angle; the actual steering angular velocity is calculated; a correction base current is set according to the steering angular velocity difference, which is the difference between the target steering angular velocity and the actual steering angular velocity; a correction coefficient is set according to the steering state determined using the actual steering angular velocity; a correction current is set using the correction base current and the correction coefficient; and the current value obtained by adding the correction current to the basic current is set as the target current. Control method.

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