Vehicular steering device

Abstract

To provide a vehicular steering device capable of determining whether a vehicle is in a running-straight state or not by a novel scheme.SOLUTION: A vehicular steering device includes: a relative steering angle detecting unit that detects a relative steering angle in accordance with the steering direction of a steering member and with a steered amount thereof; a lateral acceleration obtaining unit that obtains a lateral acceleration detection value of a vehicle; a lateral acceleration correcting unit that calculates a corrected lateral acceleration by eliminating, from the lateral acceleration detection value, a component that gives an adverse effect to the lateral acceleration detection value due to the inclination of a vehicle body relative to a horizontal plane; a running-straight state determining unit that determines, using at least the corrected lateral acceleration, whether or not the vehicle is in a running-straight state; and a steering angle midpoint updating unit that updates a steering angle midpoint based on the relative steering angle when a predetermined condition which includes at least a condition in which the vehicle is in the running-straight state is satisfied.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present disclosure relates to a vehicle steering system. [Background technology]

[0002] Patent Document 1 discloses that the steering angle midpoint is updated when a vehicle straight-line condition (straight-line driving state determination condition) that the vehicle is moving straight and a non-steering condition (non-steering state determination condition) that the steering wheel is not being steered are satisfied.

[0003] Patent Document 2 discloses that when the vehicle is traveling on a gently canted road where the vehicle is determined to be traveling straight, for example, the steering angle midpoint is not updated if the difference between the currently calculated steering angle midpoint and the most recent steering angle midpoint is equal to or greater than a certain value, in order to prevent erroneous updating of the steering angle midpoint. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-105277 A [Patent Document 2] JP 2010-261834 A Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present disclosure is to provide a vehicle steering device that can determine, using a novel method, whether or not the vehicle is traveling straight. [Means for solving the problem]

[0006] One embodiment of the present disclosure includes a relative steering angle detection unit that detects a relative steering angle corresponding to the steering direction and steering amount of a steering member, a lateral acceleration acquisition unit that acquires a lateral acceleration detection value of a vehicle, a lateral acceleration correction unit that calculates a corrected lateral acceleration by removing components that affect the lateral acceleration detection value due to the inclination of the vehicle body with respect to a horizontal plane from the lateral acceleration detection value, a straight-line running state determination unit that determines whether the vehicle is in a straight-line running state using at least the corrected lateral acceleration, and a steering angle midpoint update unit that updates the steering angle midpoint based on the relative steering angle when certain conditions are satisfied including at least the condition that the vehicle is in a straight-line running state.

[0007] With this configuration, it is possible to determine whether the vehicle is traveling straight or not using a novel method.

[0008] The above and other objects, features and advantages of the present disclosure will become apparent from the following detailed description of the embodiments with reference to the accompanying drawings. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram showing a schematic configuration of a vehicle steering device according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a block diagram showing the electrical configuration of the vehicle steering device. [Diagram 3] FIG. 3 is a block diagram showing the electrical configuration of the ECU. [Figure 4] FIG. 4 is a schematic diagram illustrating the configuration of the electric motor. [Diagram 5] FIG. 5 is a graph showing an example of setting the basic assist current value Ia with respect to the detected steering torque Td. [Figure 6] FIG. 6 is a block diagram showing the electrical configuration of the absolute steering angle calculation unit. [Figure 7] FIG. 7 is a schematic diagram for explaining the operation of the lateral acceleration correction unit. [Figure 8] FIG. 8 is a flowchart showing the procedure of the midpoint update / absolute steering angle calculation process executed by the steering angle midpoint learning unit. [Figure 9] FIG. 9 is a block diagram showing an example of the configuration of the handle return control unit. [Figure 10] FIG. 10 is a graph showing an example of setting the target steering angular velocity ωh* with respect to the absolute steering angle θha. [Figure 11] FIG. 11 is a graph showing an example of setting the basic compensation current value Iro with respect to the angular velocity deviation Δωh. [Figure 12] FIG. 12 is a graph showing an example of setting the vehicle speed gain Gv with respect to the vehicle speed V. [Figure 13] FIG. 13 is a schematic diagram for explaining a problem that occurs when a lateral acceleration detection value detected by a lateral acceleration sensor is used as it is to determine whether or not the vehicle is traveling straight ahead. [Figure 14] FIG. 14 is a schematic diagram showing a state in which the vehicle is traveling straight on a canted road. [Figure 15] FIG. 15 is a schematic diagram for explaining that if the steering angle midpoint is updated while traveling straight on a canted road as shown in FIG. 14, a negative effect occurs when the traveling road changes from a canted road to a non-canted road. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] [Description of the embodiments of the present disclosure] One embodiment of the present disclosure includes a relative steering angle detection unit that detects a relative steering angle corresponding to the steering direction and steering amount of a steering member, a lateral acceleration acquisition unit that acquires a lateral acceleration detection value of a vehicle, a lateral acceleration correction unit that calculates a corrected lateral acceleration by removing components that affect the lateral acceleration detection value due to the inclination of the vehicle body with respect to a horizontal plane from the lateral acceleration detection value, a straight-line running state determination unit that determines whether the vehicle is in a straight-line running state using at least the corrected lateral acceleration, and a steering angle midpoint update unit that updates the steering angle midpoint based on the relative steering angle when certain conditions are satisfied including at least the condition that the vehicle is in a straight-line running state.

[0011] With this configuration, it is possible to determine whether the vehicle is traveling straight or not using a novel method.

[0012] In one embodiment of the present disclosure, a cant angle calculation unit that calculates a road surface cant angle is included, and the predetermined condition includes a condition that the road surface cant angle is equal to or smaller than a predetermined threshold value.

[0013] In one embodiment of the present disclosure, the predetermined condition includes a condition that the steering wheel is in a non-steered state.

[0014] Detailed Description of the Embodiments of the Present Disclosure Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.

[0015] Fig. 1 is a schematic diagram showing a schematic configuration of a vehicle steering device according to an embodiment of the present disclosure, in which the left side of a dashed line 29 is a side view of the vehicle as seen from the side, and the right side of the dashed line 29 is a plan view of the vehicle as seen from above.

[0016] This vehicle steering device 1 includes a handle (steering wheel) 2, a steering column 4 having a steering shaft 3, a bevel gear unit 5, a power transmission shaft 6, a ball screw type hydraulic power steering mechanism (hereinafter referred to as "hydraulic power steering mechanism 7"), a steering mechanism 8, and an electric motor 9. The handle is an example of the "steering member" of the present disclosure.

[0017] The handle 2 is connected to an intermediate shaft 10 via a steering shaft 3. The intermediate shaft 10 is connected to an input shaft of a bevel gear unit 5. The output shaft of the bevel gear unit 5 is connected to an input shaft of a hydraulic power steering mechanism 7 via a power transmission shaft 6.

[0018] The steering shaft 3 includes an input shaft 3A connected to the handle 2, and an output shaft 3B connected to an intermediate shaft 10. The input shaft 3A and the output shaft 3B are connected via a torsion bar 11 so as to be capable of relative rotation.

[0019] A torque sensor 12 is disposed around the steering shaft 3. The torque sensor 12 detects the steering torque Td applied to the steering wheel 2 based on the relative rotational displacement amount between the input shaft 3A and the output shaft 3B. In this embodiment, the steering torque Td detected by the torque sensor 12 is detected, for example, as a positive value for torque for steering to the right and a negative value for torque for steering to the left, and the magnitude of the steering torque increases as the absolute value increases.

[0020] The steering mechanism 8 includes a pitman arm 21, a drag link 22, a knuckle arm 23, kingpin shafts 24, 25, a tie rod arm 26 and a tie rod 27.

[0021] One end of the pitman arm 21 is connected to a sector shaft of the hydraulic power steering mechanism 7. The other end of the pitman arm 21 is connected to one end of a drag link 22. The other end of the drag link 22 is connected to one end of a knuckle arm 23 of the right front wheel (right steered wheel) 32. The other end of the knuckle arm 23 is connected to a kingpin shaft 24 of the right front wheel 32. The kingpin shaft 24 of the right front wheel 32 and the kingpin shaft 25 of the left front wheel (left steered wheel) 31 are connected by a tie rod arm 26 and a tie rod 27. The dashed line 28 in the figure is an axle beam.

[0022] The electric motor 9 is provided on the steering column 4 and is connected to the steering shaft 3 (output shaft 3B) via a reducer (not shown). The reducer is a worm gear mechanism including a worm gear and a worm wheel that meshes with the worm gear. In the following, the reduction ratio of the reducer is represented as R. The reduction ratio R is defined as the ratio of the worm gear angle, which is the rotation angle of the worm gear, to the worm wheel angle, which is the rotation angle of the worm wheel. The rotor rotation angle of the electric motor 9 is detected by a rotation angle sensor 13.

[0023] When the steering wheel 2 is rotated, the rotational torque is transmitted to the steering shaft 3, the intermediate shaft 10, the bevel gear portion 5, the power transmission shaft 6, and the ball screw type hydraulic power steering mechanism 7, causing the pitman arm 21 to swing. Due to the swinging of the pitman arm 21, the drag link 22 is moved in the front-rear direction, the knuckle arm 23 is swingable, and the left and right front wheels (steerable wheels) 31, 32 are steered.

[0024] When the electric motor 9 is rotated, the rotational torque is transmitted to the steering shaft 3, so that the left and right front wheels (steered wheels) 31, 32 are steered via the same power transmission path as described above. In other words, by rotating the steering shaft 3 with the electric motor 9, the left and right front wheels (steered wheels) 31, 32 can be steered.

[0025] FIG. 2 is a block diagram showing the electrical configuration of the vehicle steering device.

[0026] The vehicle is equipped with a vehicle speed sensor 41 for detecting a vehicle speed V, a yaw rate sensor 42 for detecting a yaw rate YR of the vehicle, a lateral acceleration sensor 43 for detecting a lateral acceleration LA of the vehicle, a vertical acceleration sensor 44 for detecting a vertical acceleration VA of the vehicle, and stroke amounts of two suspensions (suspension stroke S) at the front of the vehicle. L ,S R ) and stroke sensors 45, 46 for detecting the rotation speed ω of each wheel. FL ,ω FR ,ω RL ,ω RR Wheel speed sensors 51 to 54 are provided for detecting the wheel speed.

[0027] Suspension stroke S L ,S R represent the stroke amount of the suspension on the front left side of the vehicle and the stroke amount of the suspension on the front right side of the vehicle, respectively. FL ,ω FR ,ω RL ,ω RRrepresent the rotation speeds of the left front wheel 31, the right front wheel 32, the left rear wheel (not shown), and the right rear wheel (not shown), respectively.

[0028] The vehicle is provided with an ECU (Electronic Control Unit) 40 for controlling the drive of the electric motor 9.

[0029] The ECU 40 receives a vehicle speed V detected by a vehicle speed sensor 41, a yaw rate YR detected by a yaw rate sensor 42, a lateral acceleration detected by a lateral acceleration sensor 43 (hereinafter referred to as a "detected lateral acceleration value LA"), a vertical acceleration VA detected by a vertical acceleration sensor 44, and a suspension stroke S detected by stroke sensors 45 and 46. L ,S R , the rotation speed ω of each wheel detected by the wheel speed sensors 51 to 54 FL ,ω FR ,ω RL ,ω RR The ECU 40 receives inputs such as a steering torque Td detected by a torque sensor 12 and an output signal from a rotation angle sensor 13. The ECU 40 controls the electric motor 9 based on these inputs.

[0030] FIG. 3 is a block diagram showing the electrical configuration of the ECU 40. As shown in FIG.

[0031] The ECU 40 includes a microcomputer 61, a drive circuit (inverter circuit) 62 that is controlled by the microcomputer 61 and supplies power to the electric motor 9, and a current detection unit 63 that detects a motor current flowing through the electric motor 9.

[0032] 4, the electric motor 9 is, for example, a three-phase brushless motor, and includes a rotor 100 as a field magnet, and a stator 105 including U-phase, V-phase, and W-phase stator windings 101, 102, 103. The electric motor 9 may be an inner rotor type in which a stator is disposed facing the outside of a rotor, or an outer rotor type in which a stator is disposed facing the inside of a cylindrical rotor.

[0033] A three-phase fixed coordinate system (UVW coordinate system) is defined with the U-axis, V-axis, and W-axis in the direction of the stator windings 101, 102, and 103 of each phase. A two-phase rotating coordinate system (dq coordinate system, real rotating coordinate system) is defined with the d-axis (magnetic pole axis) in the magnetic pole direction of the rotor 100 and the q-axis (torque axis) in a direction perpendicular to the d-axis in the rotation plane of the rotor 100. The dq coordinate system is a rotating coordinate system that rotates together with the rotor 100. In the dq coordinate system, only the q-axis current contributes to the torque generation of the rotor 100, so the d-axis current is set to zero and the q-axis current is controlled according to the desired torque. The rotation angle (electrical angle) θe of the rotor 100 is the rotation angle of the d-axis with respect to the U-axis. The dq coordinate system is a real rotating coordinate system according to the rotor rotation angle θe. By using this rotor rotation angle θe, it is possible to perform coordinate conversion between the UVW coordinate system and the dq coordinate system.

[0034] Returning to Fig. 3, the microcomputer 61 includes a CPU and memory (ROM, RAM, non-volatile memory, etc.), and functions as a plurality of functional processing sections by executing a predetermined program. The plurality of functional processing sections include a basic assist control section 71, a target current value calculation section 72, a current deviation calculation section 73, a PI (proportional integral) control section 74, a coordinate conversion section 75, a PWM (Pulse Width Modulation) control section 76, a coordinate conversion section 77, a rotation angle calculation section 78, a relative steering angle calculation section 79, a steering angular velocity calculation section 80, a vehicle body inclination calculation section 81, an absolute steering angle calculation section 82, and a steering wheel return control section 83.

[0035] The rotation angle calculation unit 78 calculates the rotation angles θe, θr of the rotor of the electric motor 9 based on the output signal of the rotation angle sensor 13. θe is an electrical angle, and θr is a mechanical angle (relative rotation angle of the rotor). The rotor rotation angle θe (electrical angle) calculated by the rotation angle calculation unit 78 is provided to each of the coordinate conversion units 75, 77. The rotation angle θr (mechanical angle) calculated by the rotation angle calculation unit 78 is provided to a relative steering angle calculation unit 79.

[0036] The relative steering angle calculation unit 79 calculates a relative steering angle θhr, which is a relative steering angle, by dividing the rotation angle θr calculated by the rotation angle calculation unit 78 by the reduction ratio R of the reduction mechanism. The relative steering angle θhr calculated by the relative steering angle calculation unit 79 is provided to a steering angular velocity calculation unit 80 and also to an absolute steering angle calculation unit 82. The relative steering angle calculation unit 79 is an example of a "relative steering angle detection unit" in this disclosure.

[0037] The steering angular velocity calculation unit 80 calculates the steering angular velocity ωh by time-differentiating the relative steering angle θhr calculated by the relative steering angle calculation unit 79. In this embodiment, when the electric motor 9 rotates in a rotation direction corresponding to the right steering direction, the steering angular velocity ωh has a positive value, and when the electric motor 9 rotates in a rotation direction corresponding to the left steering direction, the steering angular velocity ωh has a negative value.

[0038] The vehicle body inclination calculation unit 81 calculates the suspension stroke S L ,S R Based on this, the vehicle body inclination angle θtr with respect to the road surface is calculated. If the distance between the two left and right suspensions at the front of the vehicle is L, the vehicle body inclination angle θtr is calculated, for example, as follows: θ=arctan(|S R -S L | / L). The vehicle body tilt calculation unit 81 may calculate the vehicle body tilt angle θtr with respect to the road surface based on an image captured by a camera (not shown) provided on the vehicle.

[0039] The basic assist control unit 71 sets the basic assist current value Ia based on the steering torque Td detected by the torque sensor 12 and the vehicle speed V detected by the vehicle speed sensor 41. An example of setting the basic assist current value Ia with respect to the detected steering torque Td is shown in Fig. 5. The basic assist current value Ia is set to a positive value when a steering assist force for rightward steering should be generated from the electric motor 9, and is set to a negative value when a steering assist force for leftward steering should be generated from the electric motor 9. The basic assist current value Ia is positive for a positive value of the detected steering torque Td, and is negative for a negative value of the detected steering torque Td.

[0040] When the detected steering torque Td is a small value in the range (torque dead zone) of -Td1 to Td1 (for example, Td1 = 0.4 N m), the basic assist current value Ia is set to zero. When the detected steering torque Td is a value outside the range of -Td1 to Td1, the basic assist current value Ia is set so that its absolute value increases as the absolute value of the detected steering torque Td increases. Also, the basic assist current value Ia is set so that its absolute value decreases as the vehicle speed V detected by the vehicle speed sensor 41 increases. This makes it possible to generate a large steering assist force when traveling at low speeds, and to reduce the steering assist force when traveling at high speeds.

[0041] The target current value calculation unit 72 sets the current value to be passed on the coordinate axis of the dq coordinate system as the target current value based on the compensation current value Ir calculated by the steering return control unit 83 (described later) and the basic assist current value Ia. Specifically, the target current value calculation unit 72 sets the d-axis current command value I d * and the q-axis current command value I q * (Hereinafter, these will be referred to collectively as "two-phase current command value I dq * ") is set.

[0042] More specifically, the target current value calculation unit 72 calculates the q-axis current command value I q * is a significant value, while the d-axis current command value I d * More specifically, the target current value calculation unit 72 calculates a value (Ia+Ir) obtained by adding the basic assist current value Ia and the compensation current value Ir calculated by the steering wheel return control unit 83 as the q-axis current command value I q * Set as.

[0043] The two-phase current command value I set by the target current value calculation unit 72 dq * is provided to the current deviation calculation unit 73.

[0044] The current detection unit 63 detects the U-phase current I U , V phase current I V and W-phase current I W (Hereinafter, these will be referred to collectively as "three-phase detection current I UVW The three-phase detection current I UVW is provided to the coordinate conversion unit 77.

[0045] The coordinate conversion unit 77 converts the three-phase detection current I UVW (U phase current I U , V phase current I V and W-phase current I W ) into the two-phase detection current I d and I q (Hereinafter, these will be referred to collectively as "two-phase detection current I dq In this coordinate conversion, the rotor rotation angle θe calculated by the rotation angle calculation unit 78 is used.

[0046] The current deviation calculation unit 73 calculates the two-phase current command value I dq * and the two-phase detection current I given by the coordinate conversion unit 77. dq More specifically, the current deviation calculation unit 73 calculates the deviation between the d-axis current command value I d * d-axis detection current I d and the q-axis current command value I q * q-axis detected current I q These deviations are provided to the PI control unit 74.

[0047] The PI control unit 74 performs a PI calculation on the current deviation calculated by the current deviation calculation unit 73 to calculate a two-phase voltage command value V dq * (d-axis voltage command value V d * and the q-axis voltage command value V q* ) is generated. dq * is provided to the coordinate conversion unit 75.

[0048] The coordinate conversion unit 75 converts the two-phase voltage command value V dq * The three-phase voltage command value V UVW * In this coordinate conversion, the rotor rotation angle θe calculated by the rotation angle calculation unit 78 is used. The three-phase voltage command value V UVW * is the U-phase voltage command value V U * , V-phase voltage command value V V * and W-phase voltage command value V W * This three-phase voltage command value V UVW * is provided to the PWM control unit 76.

[0049] The PWM control unit 76 controls the U-phase voltage command value V U * , V-phase voltage command value V V * and W-phase voltage command value V W * The PWM control signal generator 63 generates a U-phase PWM control signal, a V-phase PWM control signal, and a W-phase PWM control signal having duties corresponding to the above-mentioned phases, respectively, and supplies these to the drive circuit 62.

[0050] The drive circuit 62 is composed of a three-phase inverter circuit corresponding to the U phase, the V phase, and the W phase. The power elements constituting this inverter circuit are controlled by a PWM control signal provided from a PWM control unit 76, thereby generating a three-phase voltage command value V UVW * A voltage equivalent to the above is applied to the stator windings 101, 102, and 103 of each phase of the electric motor 9.

[0051] The current deviation calculation unit 73 and the PI control unit 74 constitute a current feedback control means. The current feedback control means controls the motor current flowing through the electric motor 9 to be equal to or smaller than the two-phase current command value I calculated by the target current value calculation unit 72. dq * is controlled to approach

[0052] The absolute steering angle calculation unit 82 and the steering wheel return control unit 83 will be described in detail below.

[0053] FIG. 6 is a block diagram showing the electrical configuration of the absolute steering angle calculation unit 82. As shown in FIG.

[0054] The absolute steering angle calculation unit 82 includes a lateral acceleration correction unit 91 , a straight running state determination unit 92 , a non-steering state determination unit 93 , and a steering angle midpoint learning unit 94 .

[0055] The lateral acceleration correction unit 91 receives the detected lateral acceleration value LA, the vertical acceleration VA, and the inclination angle θtr of the vehicle body with respect to the road surface.

[0056] The lateral acceleration correction unit 91 calculates the road surface cant angle θc based on the vertical acceleration VA and the inclination angle θtr of the vehicle body relative to the road surface. The lateral acceleration correction unit 91 also corrects the lateral acceleration detection value LA based on the lateral acceleration detection value LA, the vertical acceleration VA, and the inclination angle θtr of the vehicle body relative to the road surface.

[0057] FIG. 7 is a schematic diagram showing a state in which the vehicle body 110 is traveling while being inclined with respect to the road surface 121 and the horizontal plane 120 due to the load 111 and the road surface cant angle θc. In FIG. 6, g is the gravitational acceleration (=9.8 m / sec 2 )

[0058] The road surface cant angle θc is a value obtained by subtracting the inclination angle θtr of the vehicle body with respect to the road surface 301 from the inclination angle θth of the vehicle body with respect to the horizontal plane 120. The lateral acceleration correction unit 91 calculates the road surface cant angle θc based on the following equation (1).

[0059] θc=θth-θtr =arccos(VA / 9.8)-θtr … (1) When the vehicle body is traveling with an inclination relative to the horizontal plane 120, the lateral acceleration detection value LA detected by the lateral acceleration sensor 43 includes a lateral acceleration component LAg caused by the gravitational acceleration g, as shown in Fig. 6. The lateral acceleration component LAg caused by the gravitational acceleration g is a component that affects the lateral acceleration detection value LA due to the inclination of the vehicle body 110 relative to the horizontal plane 120.

[0060] The lateral acceleration correction unit 91 performs correction to remove a lateral acceleration component LAg caused by the gravitational acceleration g from the lateral acceleration detection value LA. If the corrected lateral acceleration is LAc, the lateral acceleration correction unit 91 corrects the lateral acceleration detection value LA based on the following equation (2).

[0061] LAc=LA-LAg =LA-9.8×sin(θth) =LA-9.8×sin(arccos(VA / 9.8)) …(2) The corrected lateral acceleration LAc is the lateral acceleration obtained by removing the lateral acceleration component LAg caused by the gravitational acceleration g from the detected lateral acceleration value LA. When the inclination angle θth of the vehicle body with respect to the horizontal plane 120 is 0, sin(θth) is 0, so the corrected lateral acceleration LAc is equal to the detected lateral acceleration value LA.

[0062] The lateral acceleration LAc after correction by the lateral acceleration correction unit 91 is provided to a straight running state determination unit 92. The road surface cant angle θc calculated by the lateral acceleration correction unit 91 is provided to a steering angle midpoint learning unit 94.

[0063] The straight running state determination unit 92 detects the rotation speed ω FL ,ω FR ,ω RL ,ω RR The vehicle yaw rate YR and the corrected lateral acceleration LAc are input.

[0064] The straight-line running state determination unit 92 determines whether or not a predetermined straight-line running state determination condition is satisfied at each predetermined calculation cycle, and determines that the vehicle is in a straight-line running state when the predetermined straight-line running state determination condition is satisfied. The predetermined straight-line running state determination condition is that a state in which all of the following first to fourth conditions are satisfied continues for a first predetermined time or longer.

[0065] First condition: The absolute value of the "front and rear wheel speed difference" is equal to or less than a predetermined threshold A (A>0). Specifically, |ω FL -ω RL |≦A and |ω FR -ω RR |≦A.

[0066] Second condition: The absolute value of the "difference in wheel speed between the left and right wheels" is equal to or less than a predetermined threshold value B (B>0). Specifically, |ω FL -ω FR |≦B and |ω RL -ω RR |≦B.

[0067] Third condition: The absolute value |YR| of the yaw rate YR is equal to or smaller than a predetermined threshold value C (C>0).

[0068] Fourth condition: The absolute value |LAc| of the corrected lateral acceleration LAc is equal to or smaller than a predetermined threshold value D (D>0).

[0069] The predetermined straight running state determination condition may be that a state in which any one of the above-mentioned first to fourth conditions is satisfied continues for a first predetermined time or more. The predetermined straight running state determination condition may be that any one of the above-mentioned first to fourth conditions is satisfied.

[0070] The straight running state determination unit 92 provides the straight running state determination result, which indicates whether the vehicle is running in a straight running state, to the steering angle midpoint learning unit 94.

[0071] The non-steering state determination unit 93 receives the relative steering angle θhr, the steering torque Td, the steering angular velocity ωh, and the q-axis current command value I q* and is entered.

[0072] The non-steering state determination unit 93 determines whether or not a predetermined non-steering state determination condition is satisfied at each predetermined calculation cycle, and when the non-steering state determination condition is satisfied, determines that the steering wheel 2 is not being steered (non-steering state). The predetermined non-steering state determination condition is that a state in which all of the following fifth to eighth conditions are satisfied continues for a second predetermined time or longer.

[0073] Fifth condition: The absolute value |θhr| of the relative steering angle θhr is equal to or smaller than a predetermined threshold value E (E>0).

[0074] Sixth condition: The absolute value |Td| of the steering torque Td is equal to or smaller than a predetermined threshold value F (F>0).

[0075] Seventh condition: The absolute value |ωh| of the steering angular velocity ωh is equal to or smaller than a predetermined threshold value G (G>0).

[0076] Eighth condition: q-axis current command value I q * Absolute value of |I q * | is less than or equal to a predetermined threshold H (H>0).

[0077] The predetermined non-steering state determination condition may be that a state in which any one of the above-mentioned fifth to eighth conditions is satisfied continues for a second predetermined time or longer. The predetermined non-steering state determination condition may be that any one of the above-mentioned fifth to eighth conditions is satisfied.

[0078] The non-steering state determination section 93 provides the steering angle midpoint learning section 94 with a non-steering state determination result indicating whether or not the vehicle is in a non-steering state.

[0079] The steering angle midpoint learning unit 94 performs midpoint update / absolute steering angle calculation processing based on the relative steering angle θhr, the road surface cant angle θc from the lateral acceleration correction unit 91, the straight running state determination result from the straight running state determination unit 92, and the non-steering state determination result from the non-steering state determination unit 93. The steering angle midpoint learning unit 94 is an example of the "steering angle midpoint update unit" of the present disclosure.

[0080] Fig. 8 is a flowchart showing the procedure of the midpoint update / absolute steering angle calculation process executed by the steering angle midpoint learning unit 94. The process in Fig. 8 is repeatedly executed at every predetermined calculation cycle.

[0081] The steering angle midpoint learning unit 94 determines whether or not the non-steering state determination result from the non-steering state determination unit 93 indicates a non-steering state (step S1).

[0082] If the non-steered state determination result is a non-steered state (step S1: YES), the steering angle midpoint learning unit 94 determines whether the straight running state determination result from the straight running state determination unit 92 is a straight running state (step S2).

[0083] If the straight driving state determination result indicates a straight driving state (step S2: YES), the steering angle midpoint learning unit 94 determines whether the absolute value |θc| of the road surface cant angle θc is equal to or smaller than a predetermined threshold value I (I>0) (step S3).

[0084] If the absolute value |θc| of the road surface cant angle θc is equal to or smaller than the threshold value I (step S1: YES), the steering angle midpoint learning unit 94 sets the relative steering angle θhr as the midpoint steering angle θm (step S4).

[0085] Then, the steering angle midpoint learning unit 94 calculates (θhr-θm) as the absolute steering angle θha (step S5), and ends the processing for the current calculation cycle.

[0086] If it is determined in step S1 that the non-steered state determination result is not a non-steered state (step S1: NO), if it is determined in step S2 that the straight-line driving state determination result is not a straight-line driving state (step S2: NO), or if it is determined in step S3 that the absolute value |θc| of the road surface cant angle θc is greater than the threshold value I (step S2: NO), the steering angle midpoint learning unit 94 proceeds to step S6.

[0087] In step S6, the steering angle midpoint learning unit 94 sets the midpoint steering angle θm (the previous value of the midpoint steering angle θm) set in the previous calculation cycle as the midpoint steering angle θm. That is, in this case, the midpoint steering angle θm is not updated. After this, the steering angle midpoint learning unit 94 proceeds to step S5 and calculates (θhr-θm) as the absolute steering angle θha (step S5). Then, the processing of the current calculation cycle is terminated.

[0088] The steering wheel return control unit 83 generates a compensation current value (compensation current value for steering wheel return control) Ir for improving operability when returning the steering wheel 2 to the neutral position. The steering wheel return control unit 83 calculates the compensation current value Ir based on the absolute steering angle θha calculated by the absolute steering angle calculation unit 82, the vehicle speed V detected by the vehicle speed sensor 41, and the steering angular velocity ωh calculated by the steering angular velocity calculation unit 80.

[0089] FIG. 9 is a block diagram showing an example of the configuration of the handle return control unit 83.

[0090] The steering wheel returning control unit 83 includes a target steering angular velocity setting unit 201 , an angular velocity deviation calculation unit 202 , a basic compensation current value setting unit 203 , a vehicle speed gain setting unit 204 , and a vehicle speed gain multiplication unit 205 .

[0091] The target steering angular velocity setting unit 201 sets a target steering angular velocity ωh, which is a target value of the steering angular velocity, based on the absolute steering angle θha calculated by the absolute steering angle calculation unit 82. * The target steering angular velocity ωh for the absolute steering angle θha is set. * An example of setting the target steering angular velocity ωh is shown in FIG. *When the absolute steering angle θha is positive, it becomes a negative value, and when the absolute steering angle θha is negative, it becomes a positive value. When the absolute steering angle θh is a small value in the range of -θh2 to θh2, the target steering angular velocity ωh * is set to zero. When the absolute steering angle θh is outside the range of -θh2 to θh2, the target steering angular velocity ωh * is set so that its absolute value increases as the absolute value of the absolute steering angle θh increases, for example.

[0092] The angular velocity deviation calculation unit 202 calculates the target steering angular velocity ωh set by the target steering angular velocity setting unit 201. * and the deviation Δωh (=ωh * -ωh).

[0093] The basic compensation current value setting unit 203 sets the basic compensation current value Iro based on the angular velocity deviation Δωh calculated by the angular velocity deviation calculation unit 202. An example of setting the basic compensation current value Iro with respect to the angular velocity deviation Δωh is shown in Fig. 11. The basic compensation current value Iro is a positive value when the angular velocity deviation Δωh is positive, and is a negative value when the angular velocity deviation Δωh is negative. In other words, the basic compensation current value Iro is a current for generating a steering wheel returning torque.

[0094] The basic compensation current value Iro is set so that it monotonically increases from 0 to an upper limit value Iro1 (Iro1>0) as the angular velocity deviation Δωh increases when the angular velocity deviation Δωh is in the range of 0 to Δωh1 (for example, Δωh1=3 deg / sec) and is fixed at the upper limit value Iro1 when the angular velocity deviation Δωh exceeds Δωh1. The basic compensation current value Iro is also set so that it monotonically increases from 0 to a lower limit value -Iro1 as the angular velocity deviation Δωh decreases when the angular velocity deviation Δωh is in the range of 0 to -Δωh1 and is fixed at the lower limit value -Iro1 when the angular velocity deviation Δωh exceeds Δωh1.

[0095] The vehicle speed gain setting unit 204 sets the vehicle speed gain Gv based on the vehicle speed V detected by the vehicle speed sensor 41. An example of setting the vehicle speed gain Gv with respect to the vehicle speed V is shown in FIG. 12. The vehicle speed gain Gv is set to 0 when the vehicle speed V is near 0, is set to increase from 0 to 1 as the vehicle speed V increases within a range of the vehicle speed V up to V1 (for example, a predetermined value within a range of 20 km / h to 30 km / h), and is set to decrease as the vehicle speed V increases when the vehicle speed V exceeds V1. The reason why the vehicle speed gain Gv is set to decrease as the vehicle speed V increases when the vehicle speed V exceeds V1 is because it is considered that the self-aligning torque acting on the vehicle increases when the vehicle speed V exceeds V1.

[0096] The vehicle speed gain multiplication unit 205 multiplies the basic compensation current value Iro set by the basic compensation current value setting unit 203 by the vehicle speed gain Gv set by the vehicle speed gain setting unit 204 to calculate the final compensation current value Ir (=Gv·Iro).

[0097] The effects of this embodiment will be described below.

[0098] If the lateral acceleration detection value LA detected by the lateral acceleration sensor 43 is used as is to determine whether or not the vehicle is traveling straight ahead, the following problem may occur.

[0099] Case 1: As shown in FIG. 13, the vehicle is traveling straight on a road surface with a small gradient in the lateral direction relative to the vehicle's traveling direction (hereinafter, may be referred to as a "cant-free road") with the vehicle body 110 tilted relative to the road surface 121 due to the load 111. Fig. 13 is a view of the vehicle as seen from the rear. In Fig. 13, a road surface 121 is approximately horizontal with a horizontal surface 120. In Fig. 13, parts corresponding to those in Fig. 7 described above are denoted by the same reference numerals as in Fig. 7.

[0100] For example, when the vehicle is traveling straight on a road without cant, with no cargo being loaded on the vehicle body 110 and the vehicle body 110 not inclined relative to the horizontal plane 120, the absolute value |LA| of the lateral acceleration detection value detected by the lateral acceleration sensor 43 is close to zero.

[0101] However, as shown in Fig. 13, when the vehicle body 110 is tilted with respect to the horizontal plane 120 (the road surface 121 in this example) due to the load 111, the lateral acceleration component LAg caused by the gravitational acceleration g is included in the detected lateral acceleration value LA. Therefore, even if the vehicle is in a straight-ahead driving state, the absolute value |LA| of the detected lateral acceleration value does not become equal to or less than the threshold value for determining the straight-ahead driving state, and the vehicle is not determined to be in a straight-ahead driving state. Therefore, even if the vehicle is in a straight-ahead driving state, the steering angle midpoint is not updated.

[0102] Case 2: When the vehicle is loaded with the same load 111 as in case 1, the vehicle travels along a curved road that causes the vehicle body to return to its original tilt (a right curved road in the example of FIG. 13). In such a case, the turning of the vehicle may generate an acceleration in the opposite direction and of approximately the same magnitude as the lateral acceleration component LAg caused by the gravitational acceleration g in Case 1. In this case, the lateral acceleration component LAg caused by the gravitational acceleration g is canceled by the acceleration caused by the turning of the vehicle, so that the absolute value |LA| of the lateral acceleration detection value may become equal to or smaller than the threshold value for determining the straight running state even though the vehicle is not in a straight running state. In other words, in such a case, the steering angle midpoint may be updated even though the vehicle is not in a straight running state.

[0103] In the case of the above-mentioned case 1, in this embodiment, a value obtained by removing the lateral acceleration component LAg due to the gravitational acceleration g from the detected lateral acceleration value LA is calculated as the corrected lateral acceleration LAc. Therefore, the absolute value |LAc| of the corrected lateral acceleration becomes close to zero. As a result, the absolute value |LAc| of the corrected lateral acceleration is likely to be equal to or smaller than the threshold value D for determining the straight running state. Therefore, even in the case of the above-mentioned case 1, the steering angle midpoint may be updated.

[0104] In the case of the above-mentioned case 2, the lateral acceleration component LAg caused by the gravitational acceleration g is cancelled by the acceleration caused by the turning of the vehicle, so that the absolute value |LA| of the detected lateral acceleration becomes close to zero. However, in this embodiment, a value obtained by removing the lateral acceleration component LAg caused by the gravitational acceleration g from the detected lateral acceleration value LA is calculated as the corrected lateral acceleration LAc. Therefore, the absolute value |LAc| of the corrected lateral acceleration becomes larger than the absolute value |LA| of the detected lateral acceleration (a value close to zero). As a result, the absolute value |LAc| of the corrected lateral acceleration becomes more likely to become larger than the threshold value D for determining the straight running state. Therefore, in this embodiment, in the case of the case 2, the possibility of updating the steering angle midpoint is low.

[0105] In this embodiment, when the absolute value |θc| of the road surface cant angle θc is equal to or smaller than a predetermined threshold value I (I>0), the steering angle midpoint is not updated. The reason for this will be explained below.

[0106] As shown in FIG. 14, when a vehicle (including a vehicle without any cargo) that is not tilted due to cargo travels straight along a canted road 121, causing the vehicle body 110 to tilt with respect to a horizontal plane 120, the lateral acceleration component LAg caused by the gravitational acceleration g is included in the lateral acceleration detection value LA.

[0107] Fig. 14 is a view of the vehicle as seen from the rear. In Fig. 14, it is assumed that no cargo is loaded. In Fig. 14, the same reference numerals as in Fig. 7 are used to denote the same parts as in Fig. 7.

[0108] In this embodiment, the lateral acceleration component LAg due to the gravitational acceleration g is removed from the detected lateral acceleration value LA to calculate the corrected lateral acceleration LAc. Therefore, the absolute value |LAc| of the corrected lateral acceleration becomes close to zero, and is likely to be equal to or smaller than the threshold value D for determining the straight-ahead driving state.

[0109] However, in such a case, if the steering angle midpoint is updated, the following problem occurs: In order for the vehicle to travel straight on a canted road 121 as shown in Fig. 14, the steering angle position of the steering wheel 2 needs to be as shown in Fig. 15(a) (a position where the steering wheel is turned a predetermined angle to the right from the actual steering angle center shown by the dashed line in Fig. 15(a)).

[0110] In this state, when the steering angle midpoint is updated, the steering angle midpoint on the system becomes the position shown in Fig. 15(a). Therefore, after the steering angle midpoint is updated while traveling on a canted road, when the vehicle is driven straight on a road without cant, for example, by automatic driving, the system controls the steering wheel angle to the position shown in Fig. 15(a).

[0111] However, on a road without cant, if the steering wheel angle is set to the position shown in Fig. 15(a), the vehicle will not travel straight. Therefore, in order to make the vehicle travel straight, the driver must continue to apply driver torque to the steering wheel so that the steering wheel angle is in the position shown in Fig. 15(b) against the steering assist force of the system.

[0112] In this way, if the steering angle midpoint is updated while the vehicle is traveling straight on a canted road, it will have an adverse effect when the road changes from a canted road to a non-canted road. Therefore, in this embodiment, when the absolute value |θc| of the road surface cant angle θc is equal to or less than a predetermined threshold value I, the steering angle midpoint is not updated.

[0113] Although the embodiment of the present disclosure has been described above, the present disclosure can be embodied in other forms.

[0114] For example, in the above embodiment, the ECU 40 includes the basic assist control unit 71, but the ECU 40 does not necessarily need to include the basic assist control unit 71. In that case, the target current value calculation unit 72 sets the current value to be passed on the coordinate axis of the dq coordinate system as the target current value based on the compensation current value Ir calculated by the steering return control unit 83. Specifically, the target current value calculation unit 72 sets the q-axis current command value Iq * The compensation current value Ir is set as q, and the d-axis current command value I d * Set zero as

[0115] In addition, in the above-described embodiment, the relative steering angle θhr is calculated based on the output signal of the rotation angle sensor 13 for detecting the rotation angle of the rotor of the electric motor 9, but the relative steering angle θhr may also be detected based on a steering angle sensor (not shown) for detecting the relative rotation angle of the steering shaft 3.

[0116] Furthermore, in the above embodiment, the electric motor 9 is a three-phase brushless motor, but the electric motor 9 may be a motor other than a three-phase brushless motor, such as a DC motor with brushes.

[0117] Although the embodiments of the present disclosure have been described in detail, these are merely specific examples used to clarify the technical content of the present disclosure, and the present disclosure should not be interpreted as being limited to these specific examples, and the scope of the present disclosure is limited only by the appended claims. [Explanation of symbols]

[0118] 1...power steering device, 2...steering wheel, 3...steering shaft, 8...steering mechanism, 9...electric motor, 31, 32...wheels (steered wheels), 12...torque sensor, 13...rotation angle sensor, 40...ECU, 80...steering angular velocity calculation unit, 81...vehicle body inclination calculation unit, 82...absolute steering angle calculation unit, 83...steering wheel return control unit, 91...lateral acceleration correction unit, 92...straight-ahead driving state determination unit, 93...non-steering state determination unit, 94...steering angle midpoint learning unit

Claims

1. a relative steering angle detection unit that detects a relative steering angle according to a steering direction and a steering amount of a steering member; A lateral acceleration acquisition unit that acquires a detected value of a lateral acceleration of a vehicle; a lateral acceleration correction unit that calculates a corrected lateral acceleration by removing a component that affects the lateral acceleration detection value due to an inclination of the vehicle body with respect to a horizontal plane from the lateral acceleration detection value; a straight running state determination unit that determines whether or not the vehicle is in a straight running state using at least the corrected lateral acceleration; and a steering angle midpoint update unit that updates the steering angle midpoint based on the relative steering angle when predetermined conditions including at least a condition that the vehicle is in a straight-ahead driving state are satisfied.

2. A cant angle calculation unit that calculates a road surface cant angle, The vehicle steering system according to claim 1 , wherein the predetermined condition includes a condition that the road surface cant angle is equal to or smaller than a predetermined threshold value.

3. 3. The vehicle steering system according to claim 1, wherein the predetermined condition includes a condition that the steering wheel is in a non-steered state.

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