Steering control device and steering device

Abstract

While suppressing the generation of large impacts and knocking sounds (abnormal noises) caused by end collisions, it learns the position of the end of the virtual rack. The steering control device includes: a command value calculation unit (40) that calculates a current command value for an actuator that applies a steering assist force to the steering mechanism; a terminal position learning unit (46) that learns the terminal position of the steering mechanism based on the steering position of the steering mechanism detected by a position detection unit; command value correction units (41, 49) that correct the current command value calculated by the command value calculation unit (40) when the steering position detected by the position detection unit is near the learned terminal position; and correction amount limiting units (51, 52) that limit the correction amount of the current command value by the command value correction units (41, 49) based on the comparison result between the learned terminal position and a specified position, and the comparison result between the stroke length of the steering mechanism calculated based on the learned terminal position and a specified length.

Description

Technical Field

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

[0002] If the steering angle increases in the steering mechanism of a vehicle and reaches the mechanical maximum steering angle, the rack shaft of the steering mechanism reaches the end of its stroke and the steering angle cannot be further increased. The state where the rack shaft reaches the end of its stroke is referred to as "end collision". In addition, the end of the rack shaft's stroke is sometimes referred to as the "rack end".

[0003] If an end collision occurs at a high steering speed, there is a possibility of generating a large impact and knocking sound (abnormal noise), which may discomfort the driver. Patent Document 1 discloses the following technique: learning the maximum value of the absolute value of the steering angle as the rack end position, and suppressing the increase in the steering angle when the steering angle detected by the sensor is near the learned rack end position, thereby mitigating the impact during end collision.

[0004] Hereinafter, the virtual rack end position learned based on the steering angle detected by the sensor is sometimes referred to as the "virtual rack end position", and the physical actual rack end position is referred to as the "actual rack end position".

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2019-104476 Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] However, if the increase in the steering angle is suppressed to mitigate the impact during end collision before learning an appropriate position (for example, a position sufficiently close to the actual rack end position) as the virtual rack end position, it becomes difficult to steer beyond the learned value of the virtual rack end position at that time, which hinders the learning of the virtual rack end position.

[0010] On the other hand, if the mitigation of the impact during end collision is overly restricted before learning an appropriate virtual rack end position, there is a possibility of generating a large impact due to end collision, which may damage the steering mechanism.

[0011] The present invention has been made in view of the above problems, and an object thereof is to be able to learn the virtual rack end position while suppressing damage to the steering mechanism caused by end collision.

[0012] Means for Solving the Problems

[0013] In order to achieve the above object, a steering control device according to one aspect of the present invention includes: a command value calculation unit that calculates a current command value for an actuator that applies a steering assist force to a steering mechanism based on an operation of a steering operation unit acting on a vehicle; a position detection unit that detects a steering position of the steering mechanism; a terminal position learning unit that learns the terminal position of the steering mechanism based on the steering position detected by the position detection unit; a command value correction unit that corrects the current command value calculated by the command value calculation unit when the steering position detected by the position detection unit is near the terminal position learned by the terminal position learning unit; and a correction amount limiting unit that limits the correction amount of the current command value by the command value correction unit based on a comparison result between the learned terminal position and a specified position and a comparison result between the stroke length of the steering mechanism calculated based on the learned terminal position and a specified length.

[0014] In addition, a steering device according to another aspect of the present invention includes: the above-described steering control device; and an actuator that is driven and controlled by the steering control device to steer the steering wheels of the vehicle.

[0015] Advantageous Effects of the Invention

[0016] According to the present invention, it is possible to suppress the generation of large impacts and knocking sounds (abnormal noises) caused by end collisions while learning the virtual rack end position. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a schematic structural diagram showing an example of an electric power steering device according to an embodiment.

[0018] Figure 2 is a diagram showing Figure 1 an example of the functional structure of the controller shown.

[0019] Figure 3 is an explanatory diagram of an example of the range of the steering angle for implementing shock mitigation control.

[0020] Figure 4 is a block diagram showing an example of the functional structure of a shock mitigation control unit.

[0021] Figure 5 (a) of is a characteristic diagram showing a characteristic example of a spring constant table, Figure 5 and (b) of is a characteristic diagram showing a characteristic example of a viscous constant table.

[0022] Figure 6 is a block diagram showing an example of the functional structure of a terminal position learning unit.

[0023] Figure 7 (a) of is an explanatory diagram of an example of the change in the column output shaft torque accompanying the change in the steering angle,Figure 7 Figure (b) is an explanatory diagram of an example of the learned value of the terminal position when generating the column output shaft torque of (a).

[0024] Figure 8 Figure (a) is a conceptual diagram of the actual rack end position. Figure 8 Figure (b) is a conceptual diagram of the state before starting the learning of the virtual rack end position. Figure 8 Figure (c) is a conceptual diagram of the state in which the virtual rack end position on the right side has been learned. Figure 8 Figure (d) is a conceptual diagram of the state in which the virtual rack end position on the left side has been learned. Figure 8 Figure (e) is a conceptual diagram of the state in which the learning of the virtual rack end is regarded as completed. Figure 8 Figure (f) is a conceptual diagram of the state in which the learning of the virtual rack end is continued until near the actual rack end.

[0025] Figure 9 Figure (a) is a conceptual diagram of the actual rack end position. Figure 9 Figure (b) represents the same state as Figure 8 Figure (f). Figure 9 Figure (c) is a conceptual diagram of the state immediately after the offset error occurs. Figure 9 Figure (d) is a conceptual diagram of the state in which the learned position of the virtual rack end position on the left side has been updated. Figure 9 Figure (e) is a conceptual diagram of the correction of the steering angle detected by the steering angle sensor and the reset of the learned value of the virtual rack end position on the right side. Figure 9 Figure (f) is a conceptual diagram of the state in which the learned position of the virtual rack end position on the left side has been further updated. Figure 9 Figure (g) is a conceptual diagram of the state in which the learning of the virtual rack end is regarded as completed. Figure 9 Figure (h) is a conceptual diagram of the state in which the learned position of the virtual rack end position on the left side has been further updated.

[0026] Figure 10 represents Figure 8 Figures (b) to (f) of Figure 9 and a table of examples of limit values in the states of Figures (b) to (h) of Detailed Implementation Manner

[0027] With reference to the accompanying drawings, the embodiments of the present invention will be described in detail. In addition, the embodiments of the present invention shown below illustrate devices and methods for embodying the technical idea of the present invention. However, the technical idea of the present invention does not specify the structure, configuration, etc. of the constituent components as the following content. The technical idea of the present invention can be variously modified within the technical scope defined by the claims recited in the claims.

[0028] (Structure)

[0029] Figure 1 It is a schematic structural diagram showing an example of an electric power steering device according to an embodiment. The column shafts (steering shafts) 2i and 2o of the steering wheel (steering handle) 1 are connected to the steering wheels 8L and 8R via a reduction gear (worm gear) 3 forming a reduction mechanism, an intermediate shaft 4, a pinion rack mechanism 5, steering tie rods 6a and 6b, and further via hub units 7a and 7b.

[0030] The column input shaft 2i and the column output shaft 2o are connected by a torsion bar (not shown), and the torsion bar is twisted by the deviation of the rotation angle between the column input shaft 2i and the column output shaft 2o.

[0031] The intermediate shaft 4 has a shaft member 4c and universal joints 4a and 4b mounted at both ends of the shaft member. The universal joint 4a is connected to the column output shaft 2o, and the universal joint 4b is connected to the pinion rack mechanism 5.

[0032] The pinion rack mechanism 5 has: a pinion 5a connected to a pinion shaft that transmits a steering force from the universal joint 4b; and a rack 5b meshing with the pinion 5a, and converts the rotational motion transmitted to the pinion 5a into a straight-ahead motion in the vehicle width direction through the rack 5b.

[0033] A torque sensor 10 for detecting the steering torque Th is provided on the steering shaft 2 (column shafts 2i and 2o). In addition, a steering angle sensor 14 for detecting the steering angle θh of the steering wheel 1 is provided on the steering shaft 2 (column shafts 2i and 2o).

[0034] In addition, a motor 20 for assisting the steering force of the steering wheel 1 is connected to the column output shaft 2o via a reduction gear 3. Electric power is supplied from a battery 13 to a controller 30 that controls an electric power steering (EPS: Electric Power Steering) device, and an ignition key signal is input via an ignition (IGN) key 11.

[0035] In addition, the unit that gives the steering assist force is not limited to a motor, and various actuators can be used.

[0036] The controller 30 calculates a current command value of an assist control command based on the steering torque Th detected by the torque sensor 10, the vehicle speed Vh detected by a vehicle speed sensor 12, and the steering angle θh detected by the steering angle sensor 14, and controls the current supplied to the motor 20 with a voltage control command value Vref obtained by performing compensation etc. on the current command value.

[0037] In addition, the steering angle sensor 14 is not essential, and the steering angle θh can also be calculated by adding the rotation angle obtained from a rotation angle sensor that detects the rotation angle of the rotation shaft of the motor 20 to the torsion angle of the torsion bar of the torque sensor 10.

[0038] The controller 30 can, for example, include a computer having peripheral components such as a processor and a storage device. The processor can be, for example, a CPU (Central Processing Unit) or an MPU (Micro-Processing Unit).

[0039] The storage device can be any one of a semiconductor storage device, a magnetic storage device, and an optical storage device. The storage device can include memories such as registers, a cache memory, a ROM (Read Only Memory) used as a main storage device, and a RAM (Random Access Memory).

[0040] The functions of the controller 30 described below are realized, for example, by the processor of the controller 30 executing a computer program stored in the storage device.

[0041] In addition, the controller 30 can also be formed by dedicated hardware for executing each information process described below.

[0042] For example, the controller 30 can include a functional logic circuit set in a general semiconductor integrated circuit. For example, the controller 30 can have a programmable logic device (PLD) such as a field-programmable gate array (FPGA).

[0043] Figure 2 FIG. is a block diagram showing an example of the functional structure of the controller 30 according to the embodiment. The controller 30 includes a basic instruction value calculation unit 40, an adder 41, a subtractor 42, a current control unit 43, a PWM (Pulse Width Modulation) control unit 44, an inverter (INV) 45, a terminal position learning unit 46, a control rotation displacement setting unit 47, a differentiator 48, a shock mitigation control unit 49, a current detector 50, a learning state determination unit 51, and a shock mitigation control output limitation unit 52.

[0044] The basic instruction value calculation unit 40 calculates a basic current command value Iref1, which is a control target value of the drive current of the motor 20, based on the steering torque Th from the torque sensor 10 and the vehicle speed Vh from the vehicle speed sensor 12.

[0045] In the present embodiment, the value of the basic current command value Iref1 that generates the steering assist force in the right turning direction is defined as a positive value, and the value of the basic current command value Iref1 that generates the steering assist force in the left turning direction is defined as a negative value.

[0046] The adder 41 corrects the basic current command value Iref1 by adding the shock mitigation control output Iref2’ output from the shock mitigation control output limiter 52 to the basic current command value Iref1, and outputs the corrected basic current command value Iref1 as the current command value Iref3.

[0047] The shock mitigation control output limiter 52 limits the upper limit value of the shock mitigation control output Iref2 output from the shock mitigation control unit 49 using the limit values 0, Limit1, or Limit2 output from the learning state determination unit 51, and limits the lower limit value of the shock mitigation control output Iref2 using the limit values 0, (-Limit1), or (-Limit2), thereby setting the shock mitigation control output Iref2’.

[0048] When the steering angle θh approaches the rack end position, the shock mitigation control unit 49 mitigates the shock and impact noise (abnormal noise) caused by the end collision by suppressing the increase in the steering angle θh. Sometimes, the control in which the shock mitigation control unit 49 mitigates the shock and abnormal noise caused by the end collision is described as “shock mitigation control”.

[0049] The shock mitigation control unit 49 outputs the current command value that suppresses the increase in the steering angle θh in order to mitigate the shock and impact noise caused by the end collision as the shock mitigation control output Iref2. The shock mitigation control output Iref2 during right turning has a negative value, which reduces the magnitude of the positive basic current command value Iref1. On the other hand, the shock mitigation control output Iref2 during left turning has a positive value, which reduces the magnitude of the negative basic current command value Iref1. For example, the shock mitigation control unit 49 can output a current command value that generates a steering reaction force.

[0050] The shock mitigation control output limiter 52 limits the upper limit value of the shock mitigation control output Iref2 during left turning to the limit value 0 or the positive limit values Limit1, Limit2 output from the learning state determination unit 51, and limits the lower limit value of the shock mitigation control output Iref2 during right turning to the limit value 0 or the negative limit values (-Limit1), (-Limit2).

[0051] Details of the shock mitigation control unit 49 and the learning state determination unit 51 will be described later.

[0052] The current command value Iref3 calculated by the adder 41 is input to the subtractor 42, which calculates the deviation (Iref3 - Im) from the feedback motor current value Im. This deviation (Iref3 - Im) is controlled by the current control unit 43 such as PI control, and the voltage control value Vref after current control is input to the PWM control unit 44 to calculate the duty ratio, and the motor 20 is PWM-driven via the inverter 45 using the PWM signal. The motor current value Im of the motor 20 is detected by the current detector 50 and input to the subtractor 42 for feedback.

[0053] The adder 41 and the shock mitigation control unit 49 are an example of the "command value correction unit" described in the claims, and the learning state determination unit 51 and the shock mitigation control output limitation unit 52 are an example of the "correction amount limitation unit" described in the claims.

[0054] The terminal position learning unit 46 learns the virtual rack end positions θevr and θevl, which are the terminal positions of the steering mechanism, based on the steering angle θh detected by the steering angle sensor 14. θevr is the virtual rack end position during right steering and has a positive value. θevl is the virtual rack end position during left steering and has a negative value.

[0055] And sometimes an error occurs between the center position of the actual rack end positions on the left and right (hereinafter sometimes referred to as the "rack neutral position") and the neutral position of the steering angle θh of the column shaft detected by the steering angle sensor 14 (hereinafter sometimes referred to as the "steering angle neutral position"). Hereinafter, such an error is sometimes referred to as an "offset error".

[0056] The offset error is generated, for example, due to misassembly of the intermediate shaft 4. The terminal position learning unit 46 estimates the offset error Ofs and outputs the corrected steering angle θh1 obtained by subtracting the offset error Ofs from the steering angle θh detected by the steering angle sensor 14. The details of the terminal position learning unit 46 will be described later.

[0057] When the corrected steering angle θh1 is close to the rack end position and within the range where shock mitigation control is implemented (hereinafter sometimes referred to as the "shock mitigation control implementation range"), the control rotation displacement setting unit 47 sets the control rotation displacement θr indicating the degree of proximity of the corrected steering angle θh1 to the virtual rack end positions θevr and θevl.

[0058] Refer to Figure 3 . In the case of right steering (i.e., when the corrected steering angle θh1 is positive), the range where the threshold θthR < θh1 is the shock mitigation control implementation range, and in the case of left steering (i.e., when the corrected steering angle θh1 is negative), the range where the threshold θthL > θh1 is the shock mitigation control implementation range.

[0059] The threshold values θthR and θthL are set based on the virtual rack end positions θevr and θevl, respectively. For example, the threshold value θthR for right turning may be a value obtained by subtracting a positive specified value Δθ from the virtual rack end position θevr (θevr - Δθ), and the threshold value θthL for left turning may be a value obtained by adding the specified value Δθ to the virtual rack end position θevl (θevl + Δθ).

[0060] The control rotational displacement θr is set to zero ("0") outside the shock mitigation control implementation range (i.e., θthL ≤ θh1 ≤ θthR), for example. In the shock mitigation control implementation range for right turning, the larger the difference (θh1 - θthR) obtained by subtracting the threshold value θthR from the corrected steering angle θh1, the larger the set control rotational displacement θr. On the other hand, in the shock mitigation control implementation range for left turning, the smaller the difference (θh1 - θthL) obtained by subtracting the threshold value θthL from the corrected steering angle θh1 (i.e., the larger the absolute value |θh1 - θthL|), the smaller the set negative control rotational displacement θr (the larger the absolute value |θr|).

[0061] In other words, in the range where the corrected steering angle θh1 is larger than the threshold value θthR, the positive control rotational displacement θr increases corresponding to the increase in the corrected steering angle θh1, and in the range where the corrected steering angle θh1 is smaller than the threshold value θthL, the negative control rotational displacement θr decreases corresponding to the decrease in the corrected steering angle θh1.

[0062] For example, the control rotational displacement setting unit 47 may set the difference θh1 - θthR as the control rotational displacement θr when the corrected steering angle θh1 is larger than the threshold value θthR, and set the difference θh1 - θthL as the control rotational displacement θr when the corrected steering angle θh1 is smaller than the threshold value θthL.

[0063] Refer to Figure 2 The differentiator 48 differentiates the steering angle θh detected by the steering angle sensor 14 to calculate the steering angular velocity ω.

[0064] The shock mitigation control unit 49 sets the shock mitigation control output Iref2 based on the control rotational displacement θr and the steering angular velocity ω.

[0065] Figure 4 is a block diagram showing an example of the functional structure of the shock mitigation control unit 49. The shock mitigation control unit 49 includes a spring constant table 60, multipliers 61 and 63, a viscous constant table 62, an adder 64, an inverter 65, and a limiter 66.

[0066] The spring constant table 60 is a data table for calculating the spring constant k0 of the steering system. AsFigure 5 As shown in (a) of , the spring constant k0 has the characteristic of increasing relatively sharply (non-linearly increasing) in the central part of the variation region as the control rotation displacement θr increases. In addition, the characteristic when the control rotation displacement θr is negative is line-symmetric with respect to the spring constant k0 axis (vertical axis).

[0067] In addition, the viscosity constant table 62 is a data table for calculating the viscosity constant μ of the steering system. As Figure 5 shown in (b) of , the viscosity constant μ has the characteristic of gradually increasing relatively gently (non-linearly increasing) as a whole as the control rotation displacement θr increases. In addition, the characteristic when the control rotation displacement θr is negative is line-symmetric with respect to the viscosity constant μ axis (vertical axis).

[0068] The spring constant k0 from the spring constant table 60 is multiplied by the control rotation displacement θr in the multiplier 61, and the multiplication result (k0×θr) is input to the adder 64. In addition, the viscosity constant μ from the viscosity constant table 62 is multiplied by the steering angular velocity ω in the multiplier 63, and the multiplication result (μ×ω) is input to the adder 64. The addition result (=k0×θr + μ×ω) of the adder 64 is input to the inverter 65 and the limiter 66, and the shock mitigation control output Iref2 with the sign inverted and the maximum value limited is set.

[0069] In addition, Figure 4 the structure of the shock mitigation control unit 49 shown in is merely an example, and the present invention is not limited to the above structure. The shock mitigation control unit 49 only needs to have a structure capable of outputting the shock mitigation control output Iref2 that suppresses the increase in the steering angle θh when the corrected steering angle θh1 approaches the rack end position.

[0070] Next, the details of the terminal position learning unit 46 will be described. The terminal position learning unit 46 obtains the steering angle θh detected by the steering angle sensor 14 that is farthest from the steering angle neutral position among the steering angles when the rotational force applied to the steering mechanism is below the first specified value (the maximum steering angle in the case of a positive steering angle θh, and the minimum steering angle in the case of a negative steering angle θh), as the first candidate θm1 for the virtual rack end.

[0071] For example, the first candidate θm1 for the virtual rack end can be obtained when the column output shaft torque Tc applied to the column output shaft 2o is below the specified value T1.

[0072] The terminal position learning unit 46 can obtain the steering angle θh detected by the steering angle sensor 14 when the rotational force applied to the steering mechanism is equal to or less than a first specified value and the operating force applied to the steering operation unit is equal to or less than a third specified value, and take the steering angle farthest from the steering angle neutral position as the first candidate θm1 of the virtual rack end.

[0073] For example, the first candidate θm1 can be obtained when the column output shaft torque Tc is equal to or less than a specified value T1 and the steering torque Th is equal to or less than a specified value T2.

[0074] In addition, the terminal position learning unit 46 obtains the steering angle farthest from the steering angle neutral position among the angles obtained by offsetting the steering angle θh detected by the steering angle sensor 14 by a second specified value in the direction of the steering angle neutral position (that is, the angle obtained by subtracting the second specified value from the maximum steering angle in the case of a positive steering angle θh, and the angle obtained by adding the second specified value to the minimum steering angle in the case of a negative steering angle θh) as the second candidate θm2 of the virtual rack end. As the second specified value, for example, the maximum value considered to be an error can be set.

[0075] The terminal position learning unit 46 obtains the steering angle farthest from the steering angle neutral position among the first candidate θm1 and the second candidate θm2 as the virtual rack end positions θevr and θevl.

[0076] Thereby, the influence of torsion generated by torque can be reduced, and the error between the virtual rack end positions θevr and θevl and the actual rack end position can be reduced.

[0077] Figure 6 It is a block diagram showing an example of the functional structure of the terminal position learning unit 46. The terminal position learning unit 46 includes an output shaft torque calculation unit 70, a selection unit 71, a first storage unit 72, delay units 73 and 77, a rate limiter 74, a corrected position calculation unit 75, a second storage unit 76, a third storage unit 78, a limiter 79, a stroke calculation unit 80, an offset error calculation unit 81, a subtractor 82, and a terminal position correction unit 83.

[0078] The output shaft torque calculation unit 70 calculates the column output shaft torque Tc applied to the column output shaft 2o.

[0079] For example, the output shaft torque calculation unit 70 can calculate the motor torque estimated by multiplying the current command value Iref3 to the motor 20 and the motor current value Im detected by the current detector 50 by the motor torque constant and the reduction ratio of the reduction gear 3 as the column output shaft torque Tc.

[0080] For example, the output shaft torque calculation unit 70 can calculate the sum of the motor torque and the steering torque Th detected by the torque sensor 10 as the column output shaft torque Tc. The motor torque is estimated by multiplying the current command value Iref3 for the motor 20 by the motor torque constant and the reduction ratio of the reduction gear 3.

[0081] Alternatively, for example, the output shaft torque calculation unit 70 can calculate the sum of the motor torque and the steering torque Th detected by the torque sensor 10 as the column output shaft torque Tc. The motor torque is estimated by multiplying the motor current value Im detected by the current detector 50 by the motor torque constant and the reduction ratio of the reduction gear 3.

[0082] In addition, the output shaft torque calculation unit 70 can perform second-order differentiation on the detection value of the angle sensor of the motor 20 to obtain the motor angular acceleration, estimate the inertial torque by multiplying by the moment of inertia, and add the inertial torque to the column output shaft torque Tc obtained as described above.

[0083] The column output shaft torque Tc is an example of the "rotational force applied to the steering mechanism". The steering torque Th is an example of the "operating force acting on the steering operation unit of the vehicle".

[0084] The subtractor 82 subtracts the offset error Ofs calculated by the offset error calculation unit 81 from the steering angle θh detected by the steering angle sensor 14 to calculate the corrected steering angle θh1. The calculation of the offset error Ofs by the offset error calculation unit 81 will be described later.

[0085] The selector 71 selects one of the corrected steering angle θh1 and the output of the delay unit 73 based on the values of the column output shaft torque Tc and the steering torque Th and outputs it to the first storage unit 72. The delay unit 73 outputs the first candidate θm1 of the virtual rack end stored in the first storage unit 72 in a delayed manner.

[0086] For example, the selector 71 can select the corrected steering angle θh1 calculated based on the detected steering angle θh and output it to the first storage unit 72 when the column output shaft torque Tc is below a specified value T1 and the steering torque Th is below a specified value T2, and output the output of the delay unit 73 to the first storage unit 72 in other cases.

[0087] The first storage unit 72 stores, as the first candidate θm1 of the virtual rack end, the one that is farther from the steering angle neutral position among the output of the delay unit 73 and the corrected steering angle θh1.

[0088] Therefore, if the corrected steering angle θh1 calculated when the torque Tc of the column output shaft is equal to or less than the specified value T1 and the steering torque Th is equal to or less than the specified value T2 is farther from the steering angle neutral position than the first candidate θm1 previously stored in the first storage unit 72, the first candidate θm1 stored in the first storage unit 72 is updated with the corrected steering angle θh1.

[0089] In addition, the selection unit 71 can select the corrected steering angle θh1 and output it to the first storage unit 72 when the torque Tc of the column output shaft is equal to or less than the specified value T1, and output the output of the delay unit 73 to the first storage unit 72 in other cases.

[0090] The rate limiter 74 receives the first candidate θm1 output from the first storage unit 72 and the steering angle θo output from the third storage unit. The rate limiter 74 limits the change rate of the first candidate θm1 with respect to the steering angle θo delayed by a delay unit (not shown), and outputs the first candidate θm1' with the change rate limited to the third storage unit 78.

[0091] The correction position calculation unit 75 calculates an angle obtained by offsetting the corrected steering angle θh1 by a second specified value in the direction of the steering angle neutral position. That is, when the corrected steering angle θh1 is positive, an angle obtained by subtracting the second specified value from the corrected steering angle θh1 is output. When the corrected steering angle θh1 is negative, an angle obtained by adding the second specified value to the corrected steering angle θh1 is output.

[0092] The second storage unit 76 stores, as the second candidate θm2 of the virtual rack end, the one of the output of the correction position calculation unit 75 and the output of the delay unit 77 that is farther from the steering angle neutral position. The delay unit 77 outputs the second candidate θm2 of the virtual rack end stored in the second storage unit 76 in a delayed manner.

[0093] Therefore, if the output of the correction position calculation unit 75 (that is, the angle obtained by offsetting the corrected steering angle θh1 by a second specified value in the direction of the steering angle neutral position) is farther from the steering angle neutral position than the second candidate θm2 previously stored in the second storage unit 76, the second candidate θm2 stored in the second storage unit 76 is updated with the output of the correction position calculation unit 75.

[0094] The third storage unit 78 stores and outputs the steering angle θo that is farther from the steering angle neutral position among the first candidate θm1' with the change rate limited by the rate limiter 74 and the second candidate θm2.

[0095] The limiter 79 limits the magnitude of the steering angle θo output from the third storage unit 78, and outputs it as the virtual rack end positions θevr and θevl.

[0096] Refer toFigure 7 (a) and Figure 7 (b) describes an example of learning the virtual rack end of the present embodiment. For simplicity of description, the following case is described: the offset error Ofs is set to 0 (i.e., the steering angle θh = the corrected steering angle θh1), and if the steering angle θh detected when the column output shaft torque Tc is less than the predetermined value T1 is farther from the steering angle neutral position than the first candidate θm1 previously stored in the first storage unit 72, the first candidate θm1 is updated.

[0097] Figure 7 (a) is an explanatory diagram of an example of changes in the column output shaft torque Tc accompanying changes in the steering angle θh. The arrows in the diagram indicate the steering direction.

[0098] During the yaw increase steering, when the steering angle θh exceeds θ1, the column output shaft torque Tc exceeds the prescribed value T1. During the subsequent return steering, when the steering angle θh is less than θ2 (θ2>θ1), the column output shaft torque Tc is less than the prescribed value T1.

[0099] Figure 7 (b) is produced Figure 7 (a) is an explanatory diagram of an example of the learning value of the virtual rack end of the right steering when the column output shaft torque Tc is 0. The dotted line represents the steering angle θh, the single-dot chain line represents the first candidate θm1, the double-dot chain line represents the second candidate θm2, and the solid line represents the output θo from the third storage unit 78 (the virtual rack end positions θevr and θevl before being limited by the limiter 79). In addition, the single-dot chain line and the double-dot chain line are displayed in a staggered manner so as not to overlap with other lines.

[0100] If the steering angle θh increases and the yaw increase steering starts at time t1, the steering angle θh (dashed line) is learned as the first candidate θm1 (one-dot chain line) during the period when the column output shaft torque Tc is less than the predetermined value T1 (i.e., the period when the steering angle θh is less than θ1). During the yaw increase steering process, the first candidate θm1 (one-dot chain line) increases to θ1.

[0101] Furthermore, an angle obtained by subtracting the second predetermined value from the steering angle θh is learned as a second candidate θm2 (two-dot chain line).

[0102] Therefore, during the period (from time t1 to time t2) when the first candidate θm1' after the rate of change is limited by the rate of change limiter 74 is larger than the second candidate θm2 (double dotted line), the first candidate θm1' is selected as the output θo (solid line) of the third storage unit 78. If the second candidate θm2 exceeds the first candidate θm1' at time t2, the second candidate θm2 is selected as the output θo (solid line).

[0103] After that, if the increase in the steering angle θh stops at time t3 and becomes a constant value, the increase in the second candidate θm2 (double-dashed line) also stops. Therefore, the first candidate θm1' whose rate of change has been limited by the rate limiter 74 is selected as the output θo (solid line) of the third storage unit 78.

[0104] As described above, the first candidate θm1 (single-dashed line) increases to θ1. Therefore, the output θo (solid line) of the third storage unit 78 increases to θ1 with a delay compared to the first candidate θm1. When θ1 is reached at time t4, the output θo (solid line) stops increasing.

[0105] After that, if the steering angle θh starts to decrease and reverse steering starts, the steering angle θh decreases to θ2 at time t5. Then, the column output shaft torque Tc becomes equal to or less than the specified value T1. Therefore, the angle θ2 is learned as the first candidate θm1 (single-dashed line).

[0106] Therefore, the first candidate θm1' whose rate of change has been limited by the rate limiter 74 starts to increase and is selected as the output θo (solid line) of the third storage unit 78. The output θo (solid line) increases to θ2 at time t6 and then becomes constant.

[0107] If the output θo (solid line) of the third storage unit 78 learned as above, that is, the virtual rack end positions θevr and θevl before being limited by the limiter 79, are compared with the case (double-dashed line) where only the angle obtained by subtracting the second specified value (e.g., the maximum error estimated value) from the steering angle θh is learned, the output θo of the third storage unit 78 can be learned as a steering angle farther from the steering angle neutral point. Therefore, a steering angle closer to the actual rack end position can be learned as the virtual rack end positions θevr and θevl.

[0108] Next, the learning state determination unit 51 will be described. Refer to Figure 2 . The learning state determination unit 51 determines the learning state of the virtual rack end positions by the terminal position learning unit 46 based on the virtual rack end positions θevr and θevl output from the terminal position learning unit 46.

[0109] Based on the determination result of the learning state of the virtual rack end positions, the learning state determination unit 51 outputs either 0 or a positive limit value Limit1 or Limit2 to the shock mitigation control output limiting unit 52 as a limit value for limiting the upper limit value of the shock mitigation control output Iref2 during left steering.

[0110] The limit value Limit2 is a value larger than the limit value Limit1, and can be set to a sufficiently large value in a manner that can effectively prevent impacts and knocking sounds (abnormal noises) caused by end collisions. On the other hand, the limit value Limit1 can also be set to a value that allows a certain degree of impact and knocking sound (abnormal noise) but prevents damage to the steering mechanism caused by end collisions.

[0111] In addition, based on the determination result of the learning state of the virtual rack end position, the learning state determination unit 51 outputs either 0 or a negative limit value (-Limit1), (-Limit2) as the limit value for restricting the lower limit of the impact mitigation control output Iref2 to the impact mitigation control output restriction unit 52.

[0112] Specifically, as the initial values before the start of learning of the virtual rack end positions θevr and θevl, a positive initial value θint and a negative initial value (-θint) are respectively stored in the first storage unit 72, the second storage unit 76, and the third storage unit 78.

[0113] The initial values θint and (-θint) can be appropriately set in a manner that is not outside the actual rack end position (i.e., the initial values θint and (-θint) are not farther from the steering angle neutral point than the actual rack end position). For example, it can be set that θint = (minimum rack stroke - maximum rack end value).

[0114] Here, the "minimum rack stroke" can be set to the minimum value of the deviation of the value that can be calculated as the rack stroke between the virtual rack end positions θevr and θevl (e.g., the lower limit value of the manufacturing tolerance).

[0115] In addition, the "maximum rack end value" is the maximum value of the absolute value of the value that can be learned as the virtual rack end positions θevr and θevl, and can be set as the maximum rack end value = (maximum rack stroke / 2) + (estimated value of the offset error between the rack neutral position and the steering angle neutral position).

[0116] In addition, the "maximum rack stroke" is the maximum value of the deviation of the value that can be calculated as the rack stroke between the virtual rack end positions θevr and θevl. For example, it can be set to the value obtained by adding the learning error of the virtual rack end positions θevl and θevr to the upper limit value of the manufacturing tolerance.

[0117] When the right virtual rack end position θevr output from the terminal position learning unit 46 is less than the specified learning threshold θlth, the learning state determination unit 51 determines that the learning of the right virtual rack end position θevr has not been performed, and outputs "0" as the limit value for restricting the lower limit of the impact mitigation control output Iref2.

[0118] For the "learning threshold θlth", the minimum value of the absolute value of the value that can be learned as the virtual rack end positions θevr and θevl can be set. For example, the learning threshold θlth can be set to θlth = (minimum rack stroke / 2) - (estimated value of the offset error between the rack neutral position and the steering angle neutral position).

[0119] Similarly, when the virtual rack end position θevl on the left is greater than the negative learning threshold (-θlth) (that is, when the absolute value |θevl| is less than the absolute value |θlth|), it is determined that the learning of the virtual rack end position θevl on the left has not been performed, and "0" is output as the limit value for limiting the upper limit of the shock mitigation control output Iref2.

[0120] If the virtual rack end position θevr on the right becomes equal to or greater than the specified learning threshold θlth, the learning state determination unit 51 determines that the learning of the virtual rack end position θevr on the right has been performed, and "-Limit1" is output as the limit value for limiting the lower limit of the shock mitigation control output Iref2.

[0121] Similarly, when the virtual rack end position θevl on the left is less than or equal to the negative learning threshold (-θlth) (that is, when the absolute value |θevl| is greater than or equal to the absolute value |θlth|), it is determined that the learning of the virtual rack end position θevl on the left has been performed, and "Limit1" is output as the limit value for limiting the upper limit of the shock mitigation control output Iref2.

[0122] Furthermore, the learning state determination unit 51 calculates the distance between the virtual rack end position θevr on the right and the virtual rack end position θevl on the left as the rack stroke St.

[0123] If the absolute values of the learned values of the virtual rack end positions θevr and θevl increase and the rack stroke St becomes longer than the above-mentioned "minimum rack stroke", the learning state determination unit 51 determines that the learning of the virtual rack end positions θevr and θevl is completed, and "-Limit2" is output as the limit value for limiting the lower limit of the shock mitigation control output Iref2, and "Limit2" is output as the limit value for limiting the upper limit of the shock mitigation control output Iref2.

[0124] Next, an example of the case where the limit value output by the learning state determination unit 51 changes according to the change in the learning state of the virtual rack end position will be described.

[0125] Figure 8 (a) is a conceptual diagram of the actual rack end position Figure 8(b) is a conceptual diagram of the state before the start of learning of the virtual rack end position, Figure 8 (c) is a conceptual diagram of the state in which the virtual rack end position θevr on the right side has been learned, Figure 8 (d) is a conceptual diagram of the state in which the virtual rack end position θevl on the left side has been learned, Figure 8 (e) is a conceptual diagram of the state in which the learning of the virtual rack ends θevr and θevl is regarded as completed, Figure 8 (f) is a conceptual diagram of the state in which the learning of the virtual rack end continues to near the actual rack end.

[0126] In addition, Figure 10 the limit value A in the table of represents the limit value output by the learning state determination unit 51 in the state of (b) to Figure 8 (f) of Figure 8 .

[0127] In Figure 8 (b) to Figure 8 (f) of, "0 [deg]" represents the steering angle neutral position. The same applies to (b) to Figure 9 (h) described later. Figure 9

[0128] In Figure 8 (b) to Figure 8 (f) of, the steering angle neutral position and the rack neutral position (the central position of the actual rack end position) are substantially the same.

[0129] In the state before the start of learning of the virtual rack end position ((b) of Figure 8 ), the virtual rack end position θevr on the right side output from the terminal position learning unit 46 is θint with respect to the steering angle neutral position, which is smaller than the learning threshold θlth.

[0130] Therefore, the learning state determination unit 51 determines that the learning of the virtual rack end position θevr on the right side has not been performed, and outputs "0" as the limit value of the lower limit of the limit impact mitigation control output Iref2 (see Figure 10 ).

[0131] In addition, the virtual rack end position θevl on the left side output from the terminal position learning unit 46 is (-θint) with respect to the steering angle neutral position, which is larger than the learning threshold (-θlth). Therefore, the learning state determination unit 51 determines that the learning of the virtual rack end position θevl on the left side has not been performed, and outputs "0" as the limit value of the upper limit of the limit impact mitigation control output Iref2 (see Figure 10 ).

[0132] After that, as Figure 8As shown in (c), the virtual rack end position θevr on the right side is learned. Since the virtual rack end position θevr on the right side is above the learning threshold θlth, the learning state determination unit 51 determines that the learning of the virtual rack end position θevr on the right side has been performed, and outputs "-Limit1" as the limit value for the lower limit of the limit shock mitigation control output Iref2. On the other hand, since the virtual rack end position θevl on the left side remains unchanged, "0" is output as the limit value for the upper limit of the limit shock mitigation control output Iref2 (see Figure 10 ).

[0133] After that, as shown in (d) of Figure 8 , the virtual rack end position θevl on the left side is learned. Since the virtual rack end position θevl on the left side is below the negative learning threshold (-θlth), the learning state determination unit 51 determines that the learning of the virtual rack end position θevl on the left side has been performed. However, since the rack stroke St is below the minimum rack stroke, it is determined that the learning of the virtual rack end positions θevr and θevl has not been completed.

[0134] Therefore, "Limit1" is output as the limit value for the upper limit of the limit shock mitigation control output Iref2. In addition, "-Limit1" is output as the limit value for the lower limit.

[0135] After that, as shown in (e) of Figure 8 , by learning the virtual rack end position θevr on the right side, the rack stroke St becomes longer than the minimum rack stroke. Therefore, the learning state determination unit 51 determines that the learning of the virtual rack end positions θevr and θevl has been completed, and outputs "Limit2" and "-Limit2" respectively as the limit values for the upper limit and lower limit of the limit shock mitigation control output Iref2.

[0136] After that, by repeatedly learning the virtual rack end positions θevr and θevl, the virtual rack end positions θevr and θevl approach the actual rack end position (see Figure 8 of (f)).

[0137] Before the rack stroke St exceeds the maximum rack stroke, the learning state determination unit 51 outputs "Limit2" and "-Limit2" respectively as the limit values for the upper limit and lower limit of the limit shock mitigation control output Iref2.

[0138] Next, the operation in the case where an offset error occurs between the rack neutral position and the steering angle neutral position will be described. Figure 9 (a) is a conceptual diagram of the actual rack end position, Figure 9 (b) is related toFigure 8 (f) of the same figure shows a state without offset error. Figure 9 (c) of it is a conceptual diagram of the state just after the offset error occurs.

[0139] Figure 9 The steering angle neutral position of (b) is substantially the same as the rack neutral position (the central position of the actual rack end position). Figure 9 The steering angle neutral position of (c) is offset by Δθ to the right from the rack neutral position. That is, if the steering is Δθ to the left from the steering angle neutral position, the rack 5b is at the rack neutral position.

[0140] If an offset error occurs, the shock mitigation control cannot be normally implemented. In Figure 9 In the example of (c), the virtual rack end position θevr on the right side is located outside the actual rack end position, so the necessary reduction of shock and abnormal noise cannot be performed.

[0141] Therefore, the terminal position learning unit 46 estimates the offset error Ofs between the rack neutral position and the steering angle neutral position as described above, and outputs the corrected steering angle θh1 obtained by subtracting the offset error Ofs from the steering angle θh detected by the steering angle sensor 14.

[0142] Refer to Figure 6 . The stroke calculation unit 80 calculates the rack stroke St. The offset error calculation unit 81 compares the rack stroke St with the specified maximum rack stroke.

[0143] When the rack stroke St exceeds the maximum rack stroke, the offset error calculation unit 81 determines that an offset error has occurred. Then, the difference obtained by subtracting the maximum rack stroke from the rack stroke St is calculated as the offset error Ofs = (rack stroke St - maximum rack stroke).

[0144] Figure 9 (d) of it is a conceptual diagram of the state in which the virtual rack end position θevl on the left side is learned after the offset error occurs.

[0145] Since the steering angle neutral position is offset to the right from the rack neutral position, when the virtual rack end position θevl on the left side is newly learned, the rack stroke St between the virtual rack end positions θevr and θevl exceeds the maximum rack stroke. The offset error calculation unit 81 calculates the difference (rack stroke St - maximum rack stroke) obtained by subtracting the maximum rack stroke from the rack stroke St as the offset error Ofs.

[0146] In the following description, the virtual rack end position on either the left or right side, which is learned when a rack stroke St exceeding the maximum value of the rack stroke is calculated, is sometimes referred to as "one virtual rack end position". Additionally, the other virtual rack end position, which is not the one virtual rack end position among the left and right virtual rack end positions, is sometimes referred to as "the other virtual rack end position".

[0147] As Figure 9 In the example of (c), if the steering angle neutral position is shifted to the right from the rack neutral position, the left virtual rack end position becomes one virtual rack end position, and the right virtual rack end position becomes the other virtual rack end position. Conversely, if the steering angle neutral position is shifted to the left from the rack neutral position, the right virtual rack end position becomes one virtual rack end position, and the left virtual rack end position becomes the other virtual rack end position.

[0148] Refer to Figure 6 . The subtractor 82 subtracts the offset error Ofs calculated by the offset error calculation unit 81 from the steering angle θh detected by the steering angle sensor 14 to calculate the corrected steering angle θh1.

[0149] The terminal position correction unit 83 corrects the first candidate θm1 stored in the first storage unit 72, the second candidate θm2 stored in the second storage unit 76, and the steering angle θo stored in the third storage unit 78 according to the offset error Ofs. Refer to Figure 9 . (e) to explain these correction processes.

[0150] By subtracting the offset error Ofs from the steering angle θh by the subtractor 82, as Figure 9 Shown in (e), the steering angle neutral position (the position of "0 [deg]") moves.

[0151] On the other hand, in Figure 9 The left virtual rack end position θevl (i.e., one virtual rack end position) learned in (d) is the learned value before the movement of the steering angle neutral position that serves as the base point. Therefore, if the steering angle neutral position is moved as in Figure 9 In (e), the left virtual rack end position θevl needs to be corrected accordingly.

[0152] The terminal position correction unit 83 corrects the first candidate θm1 of the left virtual rack end position stored in the first storage unit 72 using the offset error Ofs. Since the left virtual rack end position is negative, it is corrected by adding the offset error Ofs. The second candidate θm2 and the steering angle θo stored in the second storage unit 76 and the third storage unit 78 are corrected in the same way.

[0153] When the end position of the virtual rack on one side is the end position of the virtual rack on the right side (i.e., when it is a positive value), the offset error Ofs is subtracted for correction.

[0154] In addition, the terminal position correction unit 83 corrects (resets) the end position of the virtual rack on the other side (the end position of the virtual rack on the right side θevr in the example of (e) in Figure 9 such that the rack stroke St between the end positions of the virtual racks θevr and θevl becomes a prescribed minimum value of the rack stroke. Thereby, the end position of the virtual rack on the other side can be corrected to be closer to the inside than the actual end position of the rack.

[0155] Refer to Figure 9 (f). If the new end position of the virtual rack on the left side θevl is further learned, the offset error calculation unit 81 calculates the change amount Δθevl of the end positions of the virtual racks θevl before and after the update.

[0156] The offset error calculation unit 81 updates the offset error Ofs by adding the change amount Δθevl to the offset error Ofs before learning the new end position of the virtual rack on the left side θevl. Thereby, the neutral position of the steering angle is further moved by the change amount Δθevl.

[0157] The terminal position correction unit 83 corrects the first candidate θm1 of the end position of the virtual rack on one side (the end position of the virtual rack on the left side) stored in the first storage unit 72 using the change amount Δθevl. Since the end position of the virtual rack on the left side is a negative value, it is corrected by adding the change amount Δθevl. The second candidate θm2 and the steering angle θo stored in the second storage unit 76 and the third storage unit 78 are corrected in the same manner.

[0158] When the end position of the virtual rack on one side is the end position of the virtual rack on the right side (i.e., when it is a positive value), it is corrected by subtracting the change amount Δθevl.

[0159] In addition, the end position of the virtual rack on the other side (the end position of the virtual rack on the right side θevr in the example of (f) in Figure 9 is corrected (reset) such that the rack stroke St between the end positions of the virtual racks θevr and θevl becomes the minimum value of the rack stroke.

[0160] Refer to Figure 9 (g). When the new end position of the virtual rack on the right side θevr (i.e., the end position of the virtual rack on the other side) is learned, the offset error calculation unit 81 does not update the offset error Ofs. That is, the neutral position of the steering angle is not moved.

[0161] In addition, the terminal position correction unit 83 also does not correct the first candidate θm1 stored in the first storage unit 72, the second candidate θm2 stored in the second storage unit 76, and the steering angle θo stored in the third storage unit 78. Thus, only the virtual rack end position θevr on the right side is updated in a manner away from the steering angle neutral position.

[0162] Refer to Figure 9 (h) of. In Figure 9 After learning the new virtual rack end position θevr on the right side in (g) of, even if further learning the new virtual rack end position θevl on the left side (i.e., one virtual rack end position), the virtual rack end position θevr on the right side is not corrected (reset) in a manner that makes the rack stroke St become the specified minimum rack stroke value.

[0163] Similar to Figure 9 (f) of, the offset error calculation unit 81 updates the offset error Ofs (i.e., corrects the steering angle neutral position) and moves, and the terminal position correction unit 83 corrects the virtual rack end position θevl on the left side. At this time, the virtual rack end position θevr on the right side is corrected by adding the offset error Ofs to the virtual rack end position θevr.

[0164] In addition, if further set as the new virtual rack end position θevr on the right side (i.e., the other virtual rack end position), the steering angle neutral position and the virtual rack end position θevl on the left side (i.e., one virtual rack end position) are not changed, and only the virtual rack end position θevr on the right side is changed.

[0165] Next, the operation of the learning state determination unit 51 in the case of generating an offset error will be described. If the rack stroke St calculated based on the virtual rack end position θevr on the right side and the virtual rack end position θevl on the left side is longer than the maximum rack stroke, the learning state determination unit 51 determines that an offset error has occurred.

[0166] In the case where it is determined that an offset error has occurred, the learning state determination unit 51 resets the limit values of the upper limit and the lower limit of the restricted shock mitigation control output Iref2 to "0" respectively.

[0167] After that, in the same manner as described above, when the right virtual rack end position θevr becomes equal to or greater than the specified learning threshold θlth, "-Limit1" is output as the limit value that limits the lower limit of the shock mitigation control output Iref2. When the left virtual rack end position θevl becomes equal to or less than the negative learning threshold (-θlth), "Limit1" is output as the limit value that limits the upper limit of the shock mitigation control output Iref2. If the rack stroke St is longer than the minimum rack stroke, "Limit2" and "-Limit2" are respectively output as the limit values that limit the upper limit and the lower limit of the shock mitigation control output Iref2.

[0168] Refer to Figure 9 (a) to Figure 9 (f) of Figure 10 and Figure 10 to illustrate an example of the limit values output by the learning state determination unit 51 when an offset error occurs. Figure 9 (b) to Figure 9 (h) of

[0169] Figure 9 (b) of Figure 8 (f) of

[0170] After that, if an offset error occurs due to, for example, incorrect assembly of the intermediate shaft 4, the state shown in Figure 9 (c) is reached. At this stage, new learning of the virtual rack ends θevr and θevl has not been performed yet, so the value of the rack stroke St calculated by the learning state determination unit 51 remains the same as the value in the state of Figure 9 (b). Therefore, the learning state determination unit 51 determines that no offset error has occurred yet, and the limit value has not been reset to "0" yet. Therefore, "Limit2" and "-Limit2" are output.

[0171] If a new left virtual rack end position θevl is learned in Figure 9 (d), the rack stroke St becomes longer than the maximum rack stroke. Therefore, the learning state determination unit 51 resets the limit values of the upper limit and the lower limit of the shock mitigation control output Iref2 to "0".

[0172] In addition, as shown in Figure 9As shown in (e), the left virtual rack end position θevl becomes equal to or less than the negative learning threshold (-θlth). Therefore, the learning state determination unit 51 determines that the learning of the left virtual rack end position θevl has been performed, and outputs "Limit1" as the limit value for limiting the upper limit of the shock mitigation control output Iref2.

[0173] On the other hand, the right virtual rack end position θevr is corrected (reset) such that the rack stroke St between the virtual rack end positions θevr and θevl becomes the minimum rack stroke. Therefore, the rack stroke St is not longer than the minimum rack stroke. Accordingly, it is determined that the learning of the virtual rack end positions θevr and θevl has not been completed. In addition, since the right virtual rack end position θevr is less than the learning threshold θlth, the output of "0" is maintained as the limit value for the lower limit of the shock mitigation control output Iref2. Figure 9 The state of (f) is the same.

[0174] Refer to Figure 9 of (g). When learning the new right virtual rack end position θevr (i.e., the virtual rack end position of the other side), when the rack stroke St becomes longer than the minimum rack stroke, the learning state determination unit 51 determines that the learning of the virtual rack end positions θevr and θevl has been completed, and outputs "Limit2" and "-Limit2" as the limit values for the upper limit and the lower limit of the shock mitigation control output Iref2, respectively.

[0175] In Figure 9 of (h), the same applies, and "Limit2" and "-Limit2" are output as the limit values for the upper limit and the lower limit of the shock mitigation control output Iref2, respectively.

[0176] As described above, the steering control device according to the present embodiment can limit the shock mitigation control output Iref2 step by step based on the comparison result between the learned virtual rack end position and the learning threshold θlth, and based on the comparison result between the rack stroke St calculated from the learned virtual rack end position and the minimum rack stroke. Thereby, it is possible to learn the virtual rack end position while suppressing damage to the steering mechanism caused by end collision.

[0177] For example, the limit value output by the learning state determination unit 51 of the present embodiment ( Figure 10 the limit value A in the table of Figure 10 is compared with the limit value B in the table of

[0178] The limit value B is in Figure 9An example of a case where, before the offset error occurs in (c), the learning state of the virtual rack end position is determined based on the learning threshold θlth and the rack stroke in the same way as the limit value A, and after the offset error occurs, the learning state is determined only by the rack stroke.

[0179] According to the limit value B, before the offset error occurs ( Figure 8 in (b) to Figure 8 (f) of), the shock mitigation control output Iref2 can be restricted step by step in the same way as the limit value A. After the offset error occurs ( Figure 9 in (d) to Figure 9 (h) of the state), according to whether the rack stroke St exceeds the minimum rack stroke, the control of whether to output the shock mitigation control output Iref2 is performed.

[0180] Therefore, after the offset error occurs, before the rack stroke St calculated based on the learning result of the virtual rack end position exceeds the minimum rack stroke, the shock mitigation control output Iref2 is restricted to "0". Since the shock mitigation control is not implemented during this period, there may be a large impact, knocking sound (abnormal sound), or damage to the steering mechanism due to end collision.

[0181] And, Figure 10 The limit value C in the table of is an example of a case where the learning state is determined only by the rack stroke.

[0182] When restricting the shock mitigation control output Iref2 using the limit value C, before the offset error occurs ( Figure 8 in (b) to Figure 8 (f) of the state) and after the offset error occurs ( Figure 9 in (d) to Figure 9 (h) of the state), the control of whether to output the shock mitigation control output Iref2 is performed according to whether the rack stroke St exceeds the minimum rack stroke.

[0183] Therefore, before the rack stroke St calculated based on the learning result of the virtual rack end position exceeds the minimum rack stroke, the shock mitigation control output Iref2 is restricted to "0". Since the shock mitigation control is not implemented during this period, there may be a large impact, knocking sound (abnormal sound), or damage to the steering mechanism due to end collision.

[0184] As described above, the embodiment in which the steering control device of the present invention is applied to an electric power steering device has been described. However, as long as the steering control device of the present invention is a steering control device that generates a force for steering the steering wheels of a vehicle through an actuator, it can also be widely applied to steering control devices other than electric power steering devices. For example, it can also be applied to a steer-by-wire (SBW) type steering device that mechanically separates the steering wheel from the steering wheels. In this case, the steering torque Th may not be added to the motor torque when calculating the column output shaft torque Tc.

[0185] In addition, a plurality of learning thresholds may be set. For example, two learning thresholds θlth1 and θlth2 (θlth1 < θlth2) may be set, and limit values "Limit11" and "Limit12" (Limit11 < Limit12 < Limit2) corresponding to the comparison result with the virtual rack end position may be set. Thereby, the change in the shock mitigation control output Iref2' can be reduced.

[0186] (Effects of the embodiment)

[0187] (1) It includes: a basic command value calculation unit 40 that calculates a current command value for a motor 20 that applies a steering assist force to a steering mechanism based on an operation of a steering operation unit acting on a vehicle; a steering angle sensor 14 that detects the steering position of the steering mechanism; a terminal position learning unit 46 that learns the terminal position of the steering mechanism based on the steering position detected by the steering angle sensor 14; a shock mitigation control unit 49 and an adder 41 that correct the current command value calculated by the command value calculation unit when the steering position detected by the steering angle sensor 14 is near the terminal position learned by the terminal position learning unit; a learning state determination unit 51 and a shock mitigation control output limitation unit 52 that limit the correction amount of the current command value by the shock mitigation control unit 49 based on the comparison result between the learned terminal position and a specified position, and the comparison result between the stroke length of the steering mechanism calculated based on the learned terminal position and a specified length.

[0188] Thereby, based on the comparison result between the learned terminal position and the specified position, and the comparison result between the stroke length calculated based on the learned terminal position and the specified length, it is possible to gradually limit the correction amount of the current command value by the shock mitigation control unit 49 according to the learning degree of the terminal position. Thereby, it is possible to learn the virtual rack end position while suppressing damage to the steering mechanism caused by end collision.

[0189] (2) The learning state determination unit 51 and the shock mitigation control output limitation unit 52 may also make the magnitude of the limitation value of the correction amount in the case where the learned end position is closer to the neutral position of the steering mechanism than the specified position and the calculated stroke length is equal to or less than the specified length smaller than the magnitude of the limitation value in the case where the learned end position is farther from the neutral position of the steering mechanism than the specified position and the calculated stroke length is equal to or less than the specified length. Thereby, it is possible to limit the correction amount of the shock mitigation control unit 49 for the current command value stepwise according to the learning degree of the end position.

[0190] (3) The learning state determination unit 51 and the shock mitigation control output limitation unit 52 may also make the magnitude of the limitation value of the correction amount in the case where the learned end position is farther from the neutral position of the steering mechanism than the specified position and the calculated stroke length is equal to or less than the specified length smaller than the magnitude of the limitation value in the case where the calculated stroke length is longer than the specified length. Thereby, it is possible to limit the correction amount of the shock mitigation control unit 49 for the current command value stepwise according to the learning degree of the end position.

[0191] (4) The end position learning unit 46 may also include: a first storage unit 72 that stores the steering position farthest from the neutral position of the steering mechanism among the steering positions detected by the position detection unit when the rotational force applied to the steering mechanism is equal to or less than a first specified value; a second storage unit 76 that stores the steering position farthest from the neutral position among the positions obtained by shifting the steering position detected by the position detection unit in the neutral direction of the steering mechanism by a second specified value; and a third storage unit 78 that stores, as the end position stored by the end position learning unit 46, the one of the steering positions stored in the first storage unit 72 and the second storage unit 76 that is farther from the neutral position.

[0192] Thereby, it is possible to learn the virtual rack end position with less influence of the torsion of the steering mechanism caused by the rotational force applied to the steering mechanism. Therefore, it is possible to reduce the error between the virtual rack end position and the actual rack end position.

[0193] (5) The terminal position learning unit 46 may also include: a stroke calculation unit 80 that calculates a rack stroke St of the steering mechanism based on the steering position detected by the position detection unit and the other terminal position of the left and right terminal positions of the steering mechanism stored in the third storage unit 78 when the position detection unit detects a steering position that is farther from the neutral position than one of the left and right terminal positions of the steering mechanism stored in the third storage unit 78; a subtractor 82 that corrects the steering position detected by the position detection unit based on the excess amount by which the rack stroke St calculated by the stroke calculation unit 80 exceeds a threshold when the rack stroke St exceeds the threshold; and a terminal position correction unit 83 that corrects the other terminal position stored in the first storage unit 72, the second storage unit 76, and the third storage unit 78 so that one terminal position is separated from the other terminal position by a predetermined interval when the rack stroke St calculated by the stroke calculation unit 80 exceeds the threshold.

[0194] Thus, even if there is an offset error between the rack neutral position and the steering angle neutral position, after absorbing the offset error and learning the virtual rack end position, it is possible to implement shock mitigation control suitable for the state of the vehicle.

[0195] (6) The terminal position learning unit 46 may store, in the first storage unit 72, the steering position detected by the position detection unit that is farthest from the neutral position of the steering mechanism when the rotational force applied to the steering mechanism is equal to or less than a first specified value and the operating force applied to the steering operation unit of the vehicle is equal to or less than a third specified value.

[0196] Thus, it is possible to learn the virtual rack end position with little influence on the torsion of the steering mechanism due to the rotational force applied to the steering mechanism and the operating force applied to the steering operation unit.

[0197] Description of reference numerals

[0198] 1…Steering wheel, 2i…Column input shaft, 2o…Column output shaft, 3…Reduction gear, 4…Intermediate shaft, 4a, 4b…Universal coupling, 4c…Shaft component, 5…Pinion rack mechanism, 5a…Pinion, 5b…Rack, 6a, 6b…Steering tie rod, 7a, 7b…Wheel hub unit, 8L, 8R…Steering wheel, 10…Torque sensor, 11…Ignition key, 12…Vehicle speed sensor, 13…Battery, 14…Steering angle sensor, 20…Motor, 30…Controller, 40…Basic command value calculation unit, 41, 64…Adder, 42, 82…Subtractor, 43…Current control unit, 44…PWM control unit, 45…Inverter, 46…Terminal position learning unit, 47…Control rotation displacement setting unit, 48…Differentiator, 49…Shock mitigation control unit, 50…Current detector, 51…Learning state determination unit, 52…Shock mitigation control output limiter, 60…Spring constant table, 61, 63…Multiplier, 62…Viscous constant table, 65…Inverter, 66, 79…Limiter, 70…Output shaft torque calculation unit, 71…Selector, 72…First storage unit, 73, 77…Delay unit, 74…Stroke limiter, 75…Correction position calculation unit, 76…Second storage unit, 78…Third storage unit, 80…Stroke calculation unit, 81…Offset error calculation unit, 83…Terminal position correction unit.

Claims

1. A steering control device, characterized in that: The steering control device includes: A command value calculation unit that calculates a current command value for an actuator based on an operation of a steering operation unit acting on a vehicle, wherein the actuator applies a steering assist force to a steering mechanism; A position detection unit that detects a steering position of the steering mechanism; An end position learning unit that learns an end position of the steering mechanism based on the steering position detected by the position detection unit; A command value correction unit that corrects the current command value calculated by the command value calculation unit when the steering position detected by the position detection unit is near the end position learned by the end position learning unit; and A correction amount limiting unit that limits a correction amount of the current command value by the command value correction unit based on a comparison result between the learned end position and a specified position, and a comparison result between a stroke length of the steering mechanism calculated based on the learned end position and a specified length.

2. The steering control device according to claim 1, characterized in that: The correction amount limiting unit makes a magnitude of a limiting value of the correction amount when the learned end position is closer to a neutral position of the steering mechanism than the specified position and the calculated stroke length is equal to or less than the specified length smaller than a magnitude of the limiting value when the learned end position is farther from the neutral position of the steering mechanism than the specified position and the calculated stroke length is equal to or less than the specified length.

3. The steering control device according to claim 1 or 2, characterized in that: The correction amount limiting unit makes a magnitude of the limiting value of the correction amount when the learned end position is farther from the neutral position of the steering mechanism than the specified position and the calculated stroke length is equal to or less than the specified length smaller than a magnitude of the limiting value when the calculated stroke length is longer than the specified length.

4. The steering control device according to claim 1 or 2, characterized in that: The end position learning unit includes: A first storage unit that stores a steering position farthest from a neutral position of the steering mechanism among the steering positions detected by the position detection unit when a rotational force applied to the steering mechanism is equal to or less than a first specified value; A second storage unit that stores a steering position farthest from the neutral position among positions obtained by offsetting the steering position detected by the position detection unit in a neutral direction of the steering mechanism by a second specified value; And A third storage unit that stores, as the end position learned by the end position learning unit, a steering position farther from the neutral position among the steering positions stored in the first storage unit and the second storage unit.

5. The steering control device according to claim 4, characterized in that: The end position learning unit includes: A stroke calculation unit that, when the position detection unit detects a steering position that is farther from the neutral position than one of the left and right terminal positions of the steering mechanism stored in the third storage unit, calculates the stroke of the steering mechanism based on the steering position detected by the position detection unit and the other terminal position of the left and right terminal positions stored in the third storage unit; A steering position correction unit that, when the stroke calculated by the stroke calculation unit exceeds a threshold value, corrects the steering position detected by the position detection unit based on the excess amount by which the stroke exceeds the threshold value; and A terminal position correction unit that, when the stroke calculated by the stroke calculation unit exceeds the threshold value, corrects the other terminal position stored in the first storage unit, the second storage unit, and the third storage unit so that the one terminal position and the other terminal position are separated by a predetermined interval.

6. The steering control device according to claim 4, wherein The terminal position learning unit stores, in the first storage unit, the steering position that is the farthest from the neutral position among the steering positions detected by the position detection unit when the rotational force is equal to or less than the first specified value and the operating force applied to the steering operation unit of the vehicle is equal to or less than the third specified value.

7. A steering device, characterized in that The steering device includes: The steering control device according to any one of claims 1 to 6; and An actuator that is driven and controlled by the steering control device to steer the steering wheel of the vehicle.

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