Actuator control device and actuator control method

Abstract

To provide an actuator control device and an actuator control method that can stably reduce impact force or collision sound when a turning mechanism stops moving by a stopper mechanism even in different turning conditions.SOLUTION: An actuator control device and an actuator control method reduce turning torque by an actuator near a location where the movement of a turning mechanism is stopped by a stopper mechanism, in accordance with an increasing turning angle of a turning wheel, then generates reaction force with the actuator, and changes, depending on turning conditions, a first turning angle for starting the generation of the reaction torque.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an actuator control device and an actuator control method. [Background technology]

[0002] The power steering device of Patent Document 1 generates an assist torque TA based on the steering angle θ and the steering angular velocity dθ / dt when the steering angle θ of the steered wheels is within a predetermined range near the steering end and the steering torque T is greater than a positive threshold value Tth. At this time, control is performed so that the assist torque TA can be in the opposite direction to the steering torque T. This reduces the impact force at the steering end, providing the driver with a good steering feel. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-260926 Summary of the Invention [Problem to be solved by the invention]

[0004] However, if the steering speed (in other words, the speed of the steering member such as the rack bar) is high just before the steering mechanism is stopped by the stopper mechanism, the impact force and collision noise will increase. Here, if the steering torque applied by the actuator to the steering mechanism is limited and the stopper mechanism suppresses the steering speed just before the steering mechanism stops moving, it is possible to reduce the impact force and collision noise. However, depending on the steering conditions, such as the friction coefficient of the road surface, the steering speed may not be sufficiently reduced, resulting in a large impact force and collision noise.

[0005] The present invention has been made in consideration of the current situation, and its object is to provide an actuator control device and an actuator control method that can stably reduce the impact force and collision noise when the steering mechanism stops moving due to a stopper mechanism, regardless of different steering conditions. [Means for solving the problem]

[0006] According to one aspect of the present invention, in the vicinity of a position where the movement of the steering mechanism is stopped by the stopper mechanism, The limit value for limiting the steering torque by the actuator is reduced in accordance with an increase in the steering angle of the steered wheels, and limit processing based on the limit value is performed. After reducing the steering torque, a reaction torque is generated by the actuator, and a first steering angle at which generation of the reaction torque is started is changed according to the steering conditions. At the same time, the second steering angle at which the limit value starts to decrease is changed in accordance with the change in the first steering angle. In another aspect, a limit value for limiting the steering torque by the actuator is reduced in accordance with an increase in the steering angle of the steered wheels near a position where the movement of the steering mechanism is stopped by a stopper mechanism, and a reaction torque is generated by the actuator after the steering torque is reduced by limit processing based on the limit value, and a first steering angle at which generation of the reaction torque starts is changed in accordance with steering conditions, and a second steering angle at which reduction of the limit value starts is fixed. In another aspect, near a position where the movement of the steering mechanism is stopped by a stopper mechanism, the steering torque by the actuator is reduced in response to an increase in the steering angle of the steered wheels, and then a reaction torque is generated by the actuator, and the first steering angle at which generation of the reaction torque begins is changed to a smaller steering angle as the friction coefficient of the road surface on which the vehicle is traveling decreases. In another aspect, the assist torque, which is the steering torque of the actuator, is controlled in accordance with the steering torque of the steering wheel applied by the driver, and the steering torque by the actuator is reduced in accordance with an increase in the steering angle of the steered wheels near a position where the movement of the steering mechanism is stopped by a stopper mechanism, and then a reaction torque is generated by the actuator, and the first steering angle at which generation of the reaction torque begins is changed to a smaller steering angle as the assist torque becomes smaller. [Effects of the Invention]

[0007] According to the present invention, the impact force and collision noise generated when the steering mechanism stops its movement by the stopper mechanism can be stably reduced even under different steering conditions. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram showing an electric power steering device. [Figure 2] FIG. 3 is a block diagram showing a function for setting a motor torque command value. [Figure 3] FIG. 10 is a diagram showing the correlation between the limit value of the assist torque, the reaction torque command, and the assist torque command value. [Figure 4] 4 is a diagram showing a shift process of a first steering angle β1 and a second steering angle β2. FIG. [Figure 5] 10 is a diagram showing a process of fixing the second steering angle β2 and shifting the first steering angle β1. FIG. [Figure 6] FIG. 10 is a diagram showing the correlation between the steering angle offset amount and the friction coefficient of the road surface. [Figure 7] FIG. 4 is a diagram showing the correlation between a steering angle offset amount and a vehicle speed. [Figure 8] FIG. 4 is a diagram showing the correlation between a steering angle offset amount and a steering angular velocity. [Figure 9] FIG. 10 is a diagram showing the correlation between a steering angle offset amount and a basic command torque. DETAILED DESCRIPTION OF THE INVENTION

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an actuator control device and an actuator control method according to the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing one embodiment of an electric power steering device 200 attached to a vehicle 100. As shown in FIG.

[0010] The steering mechanism 210 of the electric power steering device 200 basically comprises a steering wheel 201, a steering shaft 202 which is the rotation axis of the steering wheel 201, a pinion shaft 203 provided at the end of the steering shaft 202, a rack bar 204, and a rack housing 205 which accommodates the rack bar 204. In the steering mechanism 210 , when the driver of the vehicle 100 turns the steering wheel 201 , the steering torque of the driver is transmitted to the pinion shaft 203 via the steering shaft 202 .

[0011] The rotational movement of the steering shaft 202 is converted into the linear movement of the rack bar 204, which is the steering operation, by a rack-and-pinion system in which the pinion shaft 203 meshes with rack teeth formed on the rack bar 204. Left and right front wheels 110, 110, which are steered road wheels, are connected to both ends of the rack bar 204 via tie rods 250, and the steering angle of the front wheels 110, 110 is changed in accordance with the rotational movement of the pinion shaft 203.

[0012] The axial movement of the rack bar 204 is stopped by the engagement of rack ends fixed to both ends of the rack bar 204 with stoppers provided on both ends of the rack housing 205 . In other words, the rack end and the stopper portion of the rack housing 205 constitute a stopper mechanism for the rack bar 204 .

[0013] The stopper mechanism mechanically determines the range of movement of the rack bar 204, that is, the maximum amount of steering to the left from the neutral position and the maximum amount of steering to the right from the neutral position. The neutral position is a reference position where the steering angle of the front wheels 110, 110 (in other words, the front wheel steering angle) is zero, and is the position of the steering wheel 201 when the vehicle 100 is traveling straight ahead.

[0014] The steering shaft 202 is provided with an operation angle sensor 206A that detects the operation angle α of the steering shaft 202 (or the pinion shaft 203), and a steering torque sensor 206B that detects the steering torque TS (in other words, the torsion bar torque) of the steering wheel 201 by the driver. The steering mechanism 210 also includes a motor 220, which is an actuator that generates a steering torque that moves a rack bar 204, which is a steering member, in the axial direction.

[0015] The rotational motion of the motor 220 is transmitted to the rack bar 204 via a transmission mechanism 208 including a belt, a ball screw, or the like. In other words, the motor 220 and the transmission mechanism 208 constitute a drive device that moves the rack bar 204 in the axial direction.

[0016] Here, the motor 220 applies a steering torque to the rack bar 204 in order to assist the driver in rotating the steering wheel 201. Therefore, hereinafter, the steering torque that the motor 220 applies to the rack bar 204 is also referred to as assist torque.

[0017] The motor 220 is a three-phase brushless DC motor having a stator coil including U-phase, V-phase, and W-phase, and a motor rotor. The drive circuit 245 includes a three-phase bridge inverter made up of six switching elements, and controls the power supplied to the stator coil of the motor 220 by controlling the on / off of the switching elements.

[0018] The control device 230 is an actuator control device that includes a microcomputer 230A as a control section, and outputs a control signal for controlling the assist torque, which is the steering torque generated by the motor 220. The microcomputer 230A acquires a signal relating to the operating angle α output by the operating angle sensor 206A, a signal relating to the steering torque TS output by the steering torque sensor 206B, a signal relating to the vehicle speed VS output by the vehicle speed sensor 207 (or wheel speed sensor), and a signal relating to the rotation angle θ of the rotor of the motor 220 output by the motor rotation angle sensor 209. In addition, the microcomputer 230A can calculate the rotation angle of the pinion shaft 203 (hereinafter also referred to as the pinion angle) corresponding to the steering angle β of the front wheels 110, 110 by integrating the signal of the motor rotation angle θ based on the operating angle α of the steering wheel 201.

[0019] Microcomputer 230A calculates command torque Ttg, which is a command value for the torque output by motor 220, based on information such as steering torque TS, vehicle speed VS, and steering angle β (pinion angle PA). Then, the microcomputer 230A outputs a switch signal to the drive circuit 245 based on the command torque Ttg, and controls the drive current of the motor 220 by PWM (Pulse Width Modulation).

[0020] FIG. 2 is a block diagram showing the function of the microcomputer 230A for calculating the command torque Ttg, in other words, the process of the actuator control method implemented by the microcomputer 230A. The microcomputer 230A has the following functional sections: an assist torque calculation section 301, a control steering angle calculation section 302, a limit value calculation / processing section 303, a reaction force control calculation section 304, and an addition section 305.

[0021] Here, the control steering angle calculation unit 302, limit value calculation / processing unit 303, reaction force control calculation unit 304, and addition unit 305 are functional units for suppressing the steering speed near the position where the movement of the rack bar 204 is stopped by the stopper mechanism, and by these functional units suppressing the steering speed, the impact force and collision noise when the stopper mechanism comes into contact are reduced. The assist torque calculation unit 301 calculates a total assist torque TAt including a basic assist torque TAb based on the steering torque TS, the vehicle speed VS, and the like.

[0022] The limit value calculation / processing unit 303 sets a limit value TALM, which is the upper limit of the assist torque, and performs limit processing to limit the total assist torque TAt acquired from the assist torque calculation unit 301 to the limit value TALM or less. That is, if the total assist torque TAt is equal to or less than the limit value TALM, the limit value calculation / processing unit 303 outputs the total assist torque TAt as it is as the assist torque command TAtg, and if the total assist torque TAt exceeds the limit value TALM, the limit value calculation / processing unit 303 outputs the limit value TALM as the assist torque command TAtg.

[0023] As will be described in detail later, the limit value calculation / processing unit 303 performs processing to reduce the limit value TALM in accordance with an increase in the steering angle β near the position where the movement of the rack bar 204 is stopped by the stopper mechanism. Here, the control steering angle calculation unit 302 sets a signal of the steering angle β that serves as a reference when the limit value calculation / processing unit 303 reduces the limit value TALM, more specifically, a second steering angle β2 that is the steering angle β at which the reduction of the limit value TALM begins, and a first steering angle β1 (β1>β2) that is the steering angle β at which the limit value TALM becomes zero for the first time, and outputs signals related to the steering angles β1 and β2 to the limit value calculation / processing unit 303.

[0024] Then, the limit value calculation / processing unit 303 gradually decreases the limit value TALM as the steering angle β becomes larger than the second steering angle β2, so that the limit value TALM reaches zero when the steering angle β becomes the first steering angle β1, and holds the limit value TALM at zero when the steering angle β is equal to or larger than the first steering angle β1. Therefore, assist torque command TAtg output from limit value calculation / processing unit 303 gradually decreases along limit value TALM as the steering angle β increases and changes from second steering angle β2 to first steering angle β1, and is held at zero when steering angle β is equal to or larger than first steering angle β1. Here, the control steering angle calculation unit 302 variably sets at least the first steering angle β1 of the first steering angle β1 and the second steering angle β2 based on steering conditions such as the steering angular velocity Δβ, the basic assist torque TAb, the vehicle speed VS, and the friction coefficient μ of the road surface.

[0025] Furthermore, reaction force control calculation unit 304 calculates reaction torque command TRtg in accordance with the deviation angle of turning angle β from first turning angle β1 so that motor 220 generates reaction torque when turning angle β is equal to or greater than first turning angle β1 and assist torque command TAtg is limited to zero by limit value TALM.

[0026] The adder 305 adds the assist torque command TAtg after limit processing output by the limit value calculation / processing unit 303 and the reaction torque command TRtg output by the reaction force control calculation unit 304 to obtain the command torque Ttg (Ttg = TAtg + TRtg), which is the final motor torque command value. Note that reaction force control calculation unit 304 sets reaction force torque command TRtg to zero when the steering angle β is less than first steering angle β1, so that command torque Ttg matches assist torque command TAtg when the steering angle β is less than first steering angle β1. On the other hand, limit value calculation / processing unit 303 holds assist torque command TAtg at zero when steering angle β is equal to or greater than first steering angle β1, so command torque Ttg when steering angle β is equal to or greater than first steering angle β1 matches reaction torque command TRtg.

[0027] In this way, the limit value calculation / processing unit 303 performs limit processing of the total assist torque TAt based on the limit value TALM, and thereby reduces the assist torque by the motor 220 in accordance with an increase in the steering angle β near the position where the movement of the steering mechanism 210 is stopped by the stopper mechanism. Furthermore, in the region where the steering angle β exceeds the first steering angle β1, the reaction force control calculation unit 304 sets the reaction force torque command TRtg according to the deviation angle of the steering angle β from the first steering angle β1, thereby causing the motor 220 to generate a reaction force torque. In other words, the limit value calculation / processing unit 303 and the reaction force control calculation unit 304 reduce the assist torque just before the rack bar 204 is stopped from moving by the stopper mechanism, and further generate a reaction torque, thereby suppressing the steering speed and reducing the impact force and collision noise when the stopper mechanism comes into contact.

[0028] The motor torque control for suppressing the steering speed just before the rack bar 204 stops moving due to the stopper mechanism will be described in more detail below. FIG. 3 is a diagram showing one aspect of changes in limit value TALM, reaction torque command TRtg, and command torque Ttg with respect to changes in steering angle β, where the horizontal axis represents steering angle β (pinion angle) and the vertical axis represents motor torque.

[0029] The control steering angle calculation unit 302 determines the steering angle β, which is a predetermined angle before the position where the movement of the rack bar 204 is stopped by the stopper mechanism, as the second steering angle β2, which defines the steering angle region near the rack stop position, in other words, the region where control is performed to suppress the steering speed. Furthermore, the control steering angle calculation unit 302 determines the steering angle β that is closer to the stop position of the rack bar 204 than the second steering angle β2 as the first steering angle β1 (β1>β2) at which the generation of the reaction torque starts.

[0030] The second steering angle β2 is, for example, a steering angle β that is approximately 35°-40° in rotation angle of the pinion shaft 203 before the third steering angle β3, which is the stop position of the rack bar 204. Furthermore, the rotation angle of the pinion shaft 203 from the second steering angle β2 to the first steering angle β1 is set to about 30 degrees. The first steering angle β1, the second steering angle β2, and the third steering angle β3 are steering angles that satisfy β2<β1<β3.

[0031] Then, the limit value calculation / processing unit 303 maintains the limit value TALM at the standard limit value TALMb in the steering angle region including the neutral position where the steering angle β is equal to or less than the second steering angle β2. On the other hand, in a region where the steering angle β is larger than the second steering angle β2, the limit value calculation / processing unit 303 reduces the limit value TALM from the standard limit value TALMb in accordance with an increase in the steering angle β, and sets a change in the limit value TALM relative to the steering angle β so that the limit value TALM becomes zero when the steering angle β becomes the first steering angle β1 which is before the stopper position. That is, the limit value calculation / processing unit 303 reduces the assist torque command TAtg to zero as the rack approaches the stop position by limiter processing with the limit value TALM as the upper limit.

[0032] Furthermore, when the steering angle β becomes larger than the first steering angle β1, that is, after the assist torque command TAtg has decreased to zero, reaction force control calculation section 304 sets a reaction force torque command TRtg in accordance with the deviation angle of the steering angle β from the first steering angle β1, and outputs reaction force torque command TRtg as the motor torque command value. The positive motor torque in FIG. 3 is an assist torque that acts in a direction that assists the rotation of the steering wheel 201 by the driver. 3 is a torque in the opposite direction to the direction that assists the rotation of the steering wheel 201 by the driver, that is, a reaction torque that acts as a reaction force against the operation of the steering wheel 201.

[0033] Reaction force control calculation section 304 increases reaction force torque command TRtg proportionally as the deviation angle of steering angle β from first steering angle β1 increases, in other words, as steering angle β becomes larger than first steering angle β1. Here, the reaction force control calculation unit 304 limits the reaction force torque command TRtg so that it does not exceed the limit value TRLM. The reaction force control calculation unit 304 limits the reaction force torque command TRtg using the limit value TRLM, thereby preventing the driver from feeling uncomfortable due to the output of more reaction force torque than necessary.

[0034] When the steering angle β is equal to or smaller than the first steering angle β1, the reaction torque command TRtg is held at zero, and when the steering angle β is equal to or larger than the first steering angle β1, the assist torque command TAtg is held at zero. Therefore, the adder 305 adds the assist torque command TAtg, which is a positive value, and the reaction torque command TRtg, which is a negative value, but in reality, it switches between the output of the assist torque command TAtg and the output of the reaction torque command TRtg at the first steering angle β1.

[0035] In this way, the microcomputer 230A limits the assist torque command TAtg to a value smaller than the total assist torque TAt through limiting processing using the limit value TALM, and after reducing the assist torque command TAtg to zero, outputs the reaction torque command TRtg as the command torque Ttg. In other words, microcomputer 230A reduces the steering torque by motor 220 in accordance with an increase in steering angle β near the position where the movement of steering mechanism 210 is stopped by the stopper mechanism, and then causes motor 220 to generate a reaction torque. This reduces the steering speed immediately before the movement of the rack bar 204 is stopped by the stopper mechanism, reducing the impact force and collision noise when the stopper mechanism comes into contact.

[0036] Here, in a region where the steering angle β is larger than the first steering angle β1, reaction force control calculation unit 304 imparts hysteresis characteristics to the change in the steering angle β, in other words, the change in the reaction force torque command TRtg with respect to the deviation angle of the steering angle β from the first steering angle β1. In detail, the reaction force control calculation unit 304 changes the reaction force torque command TRtg from zero to the limit value TRLM between the first steering angle β1 and the fourth steering angle β4 (β2<β1<β4<β3) just before the third steering angle β3, which is the rack stop position.

[0037] Then, reaction force control calculation section 304 maintains reaction force torque command TRtg at limit value TRLM between the fourth turning angle β4 and the third turning angle β3. On the other hand, when the steering angle β returns from the third steering angle β3 toward the neutral position, reaction force control calculation section 304 gradually returns reaction force torque command TRtg from limit value TRLM toward zero, and sets reaction force torque command TRtg to zero at a fifth steering angle β5 (β1<β5<β3) that is greater than the first steering angle β1 and smaller than the third steering angle β3.

[0038] The hysteresis characteristic of the reaction torque command TRtg described above can prevent the application of the reaction torque from giving the driver an uncomfortable feeling when operating the steering wheel 201. In other words, after the rack bar 204 stops moving due to the stopper mechanism, the reaction torque becomes zero when the steering angle β returns to the fifth steering angle β5, which is greater than the first steering angle β1 at which the application of the reaction torque begins. Therefore, the driver can be prevented from feeling that the steering wheel 201 is being forcibly returned due to the application of the reaction torque.

[0039] Here, control steering angle calculation section 302 has a function of shifting the first steering angle β1, at which the application of reaction torque is started with assist torque command TAtg set to zero, in accordance with the steering conditions in the correlation between limit value TALM, reaction torque command TRtg and steering angle β shown in FIG. 3. If the characteristics of the limit value TALM and the reaction torque command TRtg with respect to the steering angle β shown in FIG. 3 are fixed, that is, if the change in motor torque immediately before the movement of rack bar 204 is stopped by the stopper mechanism is constant, depending on differences in steering conditions, such as a steering load that is smaller than standard, it may not be possible to sufficiently mitigate the impact when the stopper mechanism comes into contact, and a collision noise may occur.

[0040] In other words, when the road surface has a low friction coefficient or when the vehicle speed VS is high, the steering load is reduced, which tends to increase the steering speed. If the steering speed is high, the reduction in steering speed due to the application of reaction torque may be insufficient, which may result in increased impact force and collision noise. Therefore, when the steering conditions are such that the steering speed is faster than the steering conditions for which the standard value of the first steering angle β1 is adapted, for example, when the friction coefficient of the road surface is smaller than the standard, the control steering angle calculation unit 302 changes the first steering angle β1 at which the application of the reaction torque begins to a steering angle β that is smaller than the standard value, and advances the timing at which the application of the reaction torque begins.

[0041] As a result, the microcomputer 230A can stably reduce the impact force and collision noise when the stopper mechanism comes into contact, even if the steering conditions, such as the friction coefficient of the road surface and the vehicle speed VS, vary. When shifting the first steering angle β1 at which the application of reaction torque starts in accordance with the steering conditions, the control steering angle calculation unit 302 can shift the second steering angle β2 at which the process of reducing the limit value TALM from the standard limit value TALMb starts in accordance with the shift amount of the first steering angle β1.

[0042] FIG. 4 illustrates an example of the correlation between the steering angle β, the limit value TALM, and the reaction torque command TRtg when the first steering angle β1 and the second steering angle β2 are shifted in accordance with the steering angle offset amount AOF according to the steering conditions. The solid lines in FIG. 4 show the standard characteristics of the limit value TALM and the reaction torque command TRtg, and the dotted lines show the state in which the first steering angle β1 and the second steering angle β2 are shifted in the direction in which the steering angle β becomes smaller in accordance with the steering angle offset amount AOF according to the steering conditions.

[0043] Here, the present invention is not limited to processing in which the steering angle offset amount AOF used to shift the first steering angle β1 and the steering angle offset amount AOF used to shift the second steering angle β2 are set to the same value. That is, the control steering angle calculation unit 302 can individually set the steering angle offset amount AOF used to shift the first steering angle β1 and the steering angle offset amount AOF used to shift the second steering angle β2.

[0044] Furthermore, the control steering angle calculation unit 302 can fix the second steering angle β2 and shift the first steering angle β1 at which the application of the reaction torque starts in accordance with the steering conditions. FIG. 5 illustrates an example of the correlation between the steering angle β and the limit value TALM and the reaction torque command TRtg when the control steering angle calculation unit 302 keeps the second steering angle β2 constant regardless of the steering conditions and shifts the first steering angle β1 in accordance with the steering angle offset amount AOF according to the steering conditions. The solid lines in FIG. 5 show the standard characteristics of the limit value TALM and the reaction torque command TRtg, and the dotted lines show the state in which the first steering angle β1 is shifted in the direction in which the steering angle β becomes smaller in accordance with the steering angle offset amount AOF according to the steering conditions.

[0045] Limit value calculation / processing unit 303 and reaction force control calculation unit 304 sequentially change the correlation between steering angle β and limit value TALM and reaction force torque command TRtg in accordance with steering angles β1, β2 (steering angle offset amount AOF) determined by control steering angle calculation unit 302 in accordance with the steering conditions, and determine command torque Ttg in accordance with the updated correlation. The process of changing the first turning angle β1 and the second turning angle β2 by the control steering angle calculation unit 302, in other words, the process of setting the steering angle offset amount AOF, will be described in detail below.

[0046] The steering conditions used by control steering angle calculation section 302 to set steering angles β1, β2 (steering angle offset amount AOF) include the friction coefficient of the road surface, vehicle speed, basic assist torque TAb, and steering angular velocity Δβ. For example, the control steering angle calculation unit 302 can set the steering angle βt as the timing for acquiring information on the steering conditions to be just before the second steering angle β2, and acquire information on the steering conditions such as the friction coefficient of the road surface when the steering angle β becomes the steering angle βt.

[0047] 6 to 9 show examples of correlations between various steering conditions and the steering angle offset amount AOF, and the control steering angle calculation unit 302 sets the steering angle offset amount AOF in accordance with the characteristics shown in FIGS. 6 to 9. The steering angle offset amount AOF shown in Figures 6 to 9 is a shift amount for shifting the first steering angle β1 (and the second steering angle β2) closer to the standard, in other words, closer to the neutral position (steering angle β = 0).

[0048] FIG. 6 shows the correlation between the friction coefficient of the road surface as a steering condition and the first steering angle offset amount AOF1. Here, the control steering angle calculation unit 302 increases the first steering angle offset amount AOF1 as the friction coefficient of the road surface becomes smaller than the standard value. The standard value of the friction coefficient is, for example, the friction coefficient of a dry asphalt road surface.

[0049] Here, when the friction coefficient of the road surface becomes smaller than the standard, the steering load becomes smaller, and the steering speed tends to increase. Therefore, if the correlation between the steering angle β and the limit value TALM and the reaction torque command TRtg is adapted to a road surface with a high friction coefficient, such as a dry asphalt road surface, when vehicle 100 travels on a road surface with a low friction coefficient due to rainfall or the like, the steering speed will increase, and the reduction in steering speed due to the application of reaction torque may become insufficient, resulting in an increase in impact force and collision noise. Therefore, the control steering angle calculation unit 302 increases the first steering angle offset amount AOF1 the smaller the friction coefficient of the road surface is compared to the standard, thereby advancing the timing at which the reaction torque starts to be applied, thereby enabling the impact force and collision noise to be stably reduced even if the friction coefficient decreases.

[0050] FIG. 7 shows the correlation between the vehicle speed VS as a steering condition and the second steering angle offset amount AOF2. Here, the control steering angle calculation unit 302 increases the second steering angle offset amount AOF2 as the vehicle speed VS increases.

[0051] In other words, the faster the vehicle speed VS, the smaller the steering load becomes, making it easier for the steering speed to increase. Therefore, if the application of reaction torque is not started early, the reduction in steering speed due to the application of reaction torque may be insufficient, which may result in increased impact force and collision noise. Therefore, the control steering angle calculation unit 302 increases the second steering angle offset amount AOF2 as the vehicle speed VS increases, thereby accelerating the timing at which the reaction torque starts to be applied, thereby enabling the impact force and collision noise to be stably reduced even when the vehicle speed VS is high.

[0052] FIG. 8 shows the correlation between the steering angular velocity Δβ as a steering condition and the third steering angle offset amount AOF3. Here, the control steering angle calculation section 302 increases the third steering angle offset amount AOF3 as the steering angular velocity Δβ increases (in other words, as the rate of increase of the steering angle β increases).

[0053] In other words, the faster the turning angular velocity Δβ, the earlier the application of the reaction torque must be started, otherwise the reduction in turning velocity due to the application of the reaction torque may be insufficient, resulting in a larger impact force and collision noise. Therefore, the control steering angle calculation unit 302 increases the third steering angle offset amount AOF3 as the steering angular velocity Δβ increases, thereby advancing the timing at which the reaction torque starts to be applied, so that impact force and collision noise can be stably reduced even when the steering angular velocity Δβ increases.

[0054] FIG. 9 shows the correlation between the basic assist torque TAb and the fourth steering angle offset amount AOF4. Here, a state in which the basic assist torque TAb is small is a state in which it is estimated that the steering load is small and therefore the request for assist torque is small. Therefore, the smaller the basic assist torque TAb, the larger the control steering angle calculation section 302 sets the fourth steering angle offset amount AOF4.

[0055] In other words, the smaller the basic assist torque TAb, the earlier the reaction torque application must be started, otherwise the reduction in steering speed due to the application of the reaction torque may become insufficient, resulting in a larger impact force and collision noise. Therefore, the control steering angle calculation unit 302 increases the fourth steering angle offset amount AOF4 as the basic assist torque TAb becomes smaller, i.e., as the steering load becomes smaller, thereby advancing the timing at which the reaction torque starts to be applied, thereby enabling the impact force and collision noise to be stably reduced even when the steering load is small.

[0056] Here, the control steering angle calculation unit 302 can calculate any one of the above-mentioned first steering angle offset amount AOF1, second steering angle offset amount AOF2, third steering angle offset amount AOF3, and fourth steering angle offset amount AOF4, and shift the first steering angle β1 (and second steering angle β2) based on the calculated steering angle offset amount AOF. In addition, the control steering angle calculation unit 302 can calculate multiple values ​​from the first steering angle offset amount AOF1, the second steering angle offset amount AOF2, the third steering angle offset amount AOF3, and the fourth steering angle offset amount AOF4 described above, and shift the first steering angle β1 (and the second steering angle β2) based on the sum of the multiple steering angle offset amounts AOF or the maximum value of the multiple steering angle offset amounts AOF.

[0057] When the driver starts to turn the steering wheel 201 back toward the neutral position, the limit value calculation / processing unit 303 and the reaction force control calculation unit 304 stop applying the reaction torque and return the limit value TALM to the standard limit value TALMb, which is the upper limit value of the assist torque, thereby canceling the torque restriction for mitigating the impact force and collision noise when the steering mechanism 210 is stopped by the stopper mechanism. In other words, microcomputer 230A releases the control that reduces the steering torque by motor 220 and then generates a reaction torque by motor 220 when the driver starts to turn steering wheel 201 back toward the neutral position.

[0058] Furthermore, the microcomputer 230A can perform control to suppress the rotation speed N [rpm] of the motor 220 in order to maintain the effectiveness of the process of reducing the steering speed by applying the reaction torque. Motor 220, which is a DC motor, has a limit characteristic (TN characteristic) in which torque decreases as the rotation speed N [rpm] increases, and the higher the rotation speed N, the smaller the torque that can be generated. Therefore, even if the microcomputer 230A attempts to suppress the steering speed by generating a reaction torque using the motor 220 just before the rack stop position, if the rotation speed N is high, there is a risk that the desired reaction torque (limit value TRLM) will not be generated.

[0059] Therefore, the microcomputer 230A limits the command torque Ttg so that the upper limit of the motor rotation speed (upper limit of the steering angular velocity) at which a desired reaction torque can be generated is not exceeded. This makes it possible to stably generate the desired reaction torque (reaction force upper limit value TALMc) immediately before the rack stop position, thereby maintaining the effectiveness of torque restriction for mitigating collision noise.

[0060] The technical ideas explained in the above embodiments can be used in appropriate combinations as long as no contradiction occurs. Furthermore, although the contents of the present invention have been specifically described with reference to preferred embodiments, it is obvious that a person skilled in the art can adopt various modified embodiments based on the basic technical idea and teachings of the present invention.

[0061] In the embodiment described above, the steering torque control according to the present invention is applied to the electric power steering device 200 in which the steering wheel 201 and the front wheels 110, 110 that are steered wheels are mechanically connected. However, the steering torque control according to the present invention can also be applied to a steer-by-wire type steering system that does not have a mechanical connection between the steering wheel 201 and the front wheels 110, 110.

[0062] In other words, when the steering torque generated by the actuator provided in the steering device of the steer-by-wire steering system is controlled based on a steering angle command, the steering torque can be reduced and a reaction torque can be applied so that the steering speed does not become excessive near the rack stop position, and the timing at which the reaction torque application begins can be changed depending on steering conditions such as the friction coefficient of the road surface and vehicle speed. [Explanation of symbols]

[0063] 100...vehicle, 110...front wheels (steered wheels), 200...electric power steering device, 201...steering wheel, 204...rack bar, 205...rack housing, 210...steering mechanism, 220...motor (actuator), 230...control device (actuator control device), 230A...microcomputer (control unit), β1...first steering angle, β2...second steering angle

Claims

1. An actuator control device having a control unit that outputs a control signal to an actuator that applies a steering torque to a steering mechanism to steer steered wheels of a vehicle, The control unit a limit value for limiting the steering torque by the actuator is reduced in accordance with an increase in the steering angle of the steered wheels near a position where the movement of the steering mechanism is stopped by a stopper mechanism, and a reaction torque is generated by the actuator after the steering torque is reduced by limit processing based on the limit value, a first steering angle at which generation of the reaction torque is started is changed in accordance with a steering condition, and a second steering angle at which reduction of the limit value is started is changed in accordance with a change in the first steering angle; Actuator control device.

2. An actuator control device having a control unit that outputs a control signal to an actuator that applies a steering torque to a steering mechanism to steer steered wheels of a vehicle, The control unit a limit value for limiting the steering torque by the actuator is reduced in accordance with an increase in the steering angle of the steered wheels near a position where the movement of the steering mechanism is stopped by a stopper mechanism, and a reaction torque is generated by the actuator after the steering torque is reduced by limit processing based on the limit value, a first steering angle at which the reaction torque starts to be generated is changed in accordance with a steering condition, and a second steering angle at which the limit value starts to decrease is fixed; Actuator control device.

3. An actuator control device having a control unit that outputs a control signal to an actuator that applies a steering torque to a steering mechanism to steer steered wheels of a vehicle, The control unit near a position where the movement of the steering mechanism is stopped by a stopper mechanism, the steering torque by the actuator is reduced in response to an increase in the steering angle of the steered wheels, and then a reaction torque is generated by the actuator, the first steering angle at which the generation of the reaction torque is started is changed to a smaller steering angle as the friction coefficient of the road surface on which the vehicle is traveling decreases; Actuator control device.

4. An actuator control device having a control unit that outputs a control signal to an actuator that applies a steering torque to a steering mechanism to steer steered wheels of a vehicle, The control unit controlling an assist torque, which is a steering torque of the actuator, in response to a steering torque of the steering wheel applied by a driver; near a position where the movement of the steering mechanism is stopped by a stopper mechanism, the steering torque by the actuator is reduced in response to an increase in the steering angle of the steered wheels, and then a reaction torque is generated by the actuator, The first steering angle at which the generation of the reaction torque is started is changed to a smaller steering angle as the assist torque becomes smaller. Actuator control device.

5. An actuator control method for controlling an actuator that applies a steering torque to a steering mechanism to steer steered wheels of a vehicle, the method comprising: a limit value for limiting the steering torque by the actuator is reduced in accordance with an increase in the steering angle of the steered wheels near a position where the movement of the steering mechanism is stopped by a stopper mechanism, and a reaction torque is generated by the actuator after the steering torque is reduced by limit processing based on the limit value; a first steering angle at which generation of the reaction torque is started is changed in accordance with a steering condition, and a second steering angle at which reduction of the limit value is started is changed in accordance with a change in the first steering angle; Actuator control method.

6. An actuator control method for controlling an actuator that applies a steering torque to a steering mechanism to steer steered wheels of a vehicle, the method comprising: a limit value for limiting the steering torque by the actuator is reduced in accordance with an increase in the steering angle of the steered wheels near a position where the movement of the steering mechanism is stopped by a stopper mechanism, and a reaction torque is generated by the actuator after the steering torque is reduced by limit processing based on the limit value; a first steering angle at which the reaction torque starts to be generated is changed in accordance with a steering condition, and a second steering angle at which the limit value starts to decrease is fixed; Actuator control method.

7. An actuator control method for controlling an actuator that applies a steering torque to a steering mechanism to steer steered wheels of a vehicle, the method comprising: near a position where the movement of the steering mechanism is stopped by a stopper mechanism, in response to an increase in the steering angle of the steered wheels, the steering torque by the actuator is reduced and then a reaction torque is generated by the actuator; the first steering angle at which the generation of the reaction torque is started is changed to a smaller steering angle as the friction coefficient of the road surface on which the vehicle is traveling decreases; Actuator control method.

8. An actuator control method for controlling an actuator that applies a steering torque to a steering mechanism to steer steered wheels of a vehicle, the method comprising: controlling an assist torque, which is a steering torque of the actuator, in response to a steering torque of the steering wheel applied by a driver; near a position where the movement of the steering mechanism is stopped by a stopper mechanism, in response to an increase in the steering angle of the steered wheels, the steering torque by the actuator is reduced and then a reaction torque is generated by the actuator; The first steering angle at which the generation of the reaction torque is started is changed to a smaller steering angle as the assist torque becomes smaller. Actuator control method.

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