Electric power steering device

Abstract

This electric power steering device (20) applies torque to a steering mechanism of a vehicle (10). The vehicle (10) is configured such that a turning angle (θw) of turned wheels (13) changes according to a vehicle orientation (L1). The electric power steering device (20) has a motor (23) that generates torque and a steering control device (60) that controls the motor (23) in accordance with a steering state. The steering control device (60) is configured to control the motor (23) so as to correct the change in the turning angle (θw) in accordance with a vehicle orientation (L1) detected via an onboard sensor (63), on the basis of the correlation between the vehicle orientation (L1) and the change in the turning angle (θw).

Description

[Technical Field]

[0001] The present disclosure relates to an electric power steering device. [Background technology]

[0002] Conventionally, so-called cab-over vehicles, such as trucks, in which the driver's seat is located forward of the front axle, often use an axle-type suspension in which the left and right wheels are connected by an axle. Vehicles with an axle-type suspension often use a ball screw type steering gearbox. The steering gearbox is mounted on, for example, the vehicle frame.

[0003] The electric power steering device in Patent Document 1 has a motor and a ball screw type steering gearbox. The steering gearbox converts the rotational motion of the steering shaft into the swinging motion of a pitman arm. The direction of the steered wheels is changed in conjunction with the pitman arm. The torque of the motor is transmitted to the ball screw shaft of the steering gearbox via a reducer. This assists the steering of the steering wheel. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-156082 Summary of the Invention [Problem to be solved by the invention]

[0005] In axle-suspended vehicles, especially those with cargo carrying facilities such as freight trucks, the vertical position of the vehicle frame changes significantly depending on the load condition. As a result, the vertical position of the steering gearbox mounted on the vehicle frame also changes. Because the pitman arm and the steered wheels are connected by a link mechanism, the steering position (steering angle) of the steered wheels changes in response to changes in the position of the steering gearbox. A similar phenomenon occurs when the vehicle is accelerating or decelerating.

[0006] Therefore, there is a concern that the relationship between the steering angle of the steering wheel and the steered angle of the steered wheels may change to a different relationship from the original relationship corresponding to the steering angle ratio, which is the ratio between the steering wheel and the steered angle, depending on the load condition of the goods or the running condition of the vehicle. For example, even if the rotation position of the steering wheel is at the steering neutral position corresponding to the straight-ahead state of the vehicle, the steered position of the steered wheels may be at a position different from the steering neutral position corresponding to the straight-ahead state of the vehicle. [Means for solving the problem]

[0007] An electric power steering device according to one aspect of the present disclosure applies torque to a steering mechanism of a vehicle. The vehicle is configured so that the steering angle of steered wheels changes depending on the vehicle attitude. The electric power steering device has a motor configured to generate the torque and a steering control device configured to control the motor depending on the steering state. The steering control device is configured to control the motor to correct the change in the steering angle depending on the vehicle attitude detected by an on-board sensor, based on the correlation between the vehicle attitude and the change in the steering angle. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram of an embodiment of an electric power steering device; [Figure 2] FIG. 2 is a cross-sectional view of the steering gear box of FIG. 1. [Figure 3] FIG. 2 is a block diagram of a steering control device that controls the motor in FIG. [Figure 4]FIG. 2 is a side view of a vehicle on which the electric power steering device of FIG. 1 is mounted. [Figure 5] FIG. 2 is a schematic view showing sinking of the body frame of FIG. 1. [Figure 6] FIG. 4 is a block diagram showing the configuration of the steering control device of FIG. 3. [Figure 7] 6 is a graph showing the relationship between the amount of sinking of the body frame of FIG. 5 and the correction angle. [Figure 8] 2 is a schematic diagram illustrating a process for correcting the steering angle of the steered wheels in FIG. 1; DETAILED DESCRIPTION OF THE INVENTION

[0009] An electric power steering device according to an embodiment will be described. <Overall structure> As shown in FIG. 1, the electric power steering device 20 is mounted on, for example, a cab-over vehicle 10. The vehicle 10 is equipped with an axle-suspended suspension 11. The suspension 11 supports a front axle 12. Steerable wheels 13, which are front wheels, are connected to both ends of the front axle 12. The suspension 11 has a leaf spring 14. As an example, the leaf spring 14 is located above the front axle 12. The leaf spring 14 extends in the longitudinal direction of the vehicle. Both ends of the leaf spring 14 are attached to a body frame 16 via support members 15, such as shackles.

[0010] The electric power steering device 20 has a steering shaft 21, a steering gear box 22, and a motor 23. The steering shaft 21 and the steering gear box 22 constitute a steering mechanism of the vehicle 10. A first end of the steering shaft 21 is connected to a steering wheel 24. A second end of the steering shaft 21 is connected to the steering gear box 22. The motor 23 is connected to the steering gear box 22 via a reducer 25. The steering gear box 22 is, for example, an RBS type (recirculating ball screw type) steering gear box.

[0011] The steering gear box 22 is connected to the steered wheels 13 via a link mechanism 30. The link mechanism 30 has a pitman arm 31, a drag link 32, and a tie rod 33. The base end of the pitman arm 31 is connected to a side portion of the steering gear box 22. The pitman arm 31 is swingable in the front-to-rear direction of the vehicle around its base end. A first end of the drag link 32 is rotatably connected to the tip of the pitman arm 31. A second end of the drag link 32 is rotatably connected to a knuckle arm 34 of the right steered wheel 13. Both ends of the tie rod 33 are connected to the left and right steered wheels 13 via tie rod arms 35.

[0012] The rotation of the steering wheel 24 is transmitted to the steering gear box 22 via the steering shaft 21. The steering gear box 22 converts the rotational motion of the steering shaft 21 into the swinging motion of a pitman arm 31. The swinging motion of the pitman arm 31 drives a drag link 32 in the front-to-rear direction of the vehicle. The knuckle arm 34 swings in conjunction with the drag link 32, causing the steered wheels 13 to turn.

[0013] The motor 23 generates torque in the same direction as the steering direction of the steering wheel 24. The torque of the motor 23 is transmitted to the steering shaft 21 via the reducer 25 and the steering gear box 22. This assists the steering of the steering wheel 24.

[0014] <Steering gear box> 2, the steering gear box 22 has a housing 40. Inside the housing 40, a ball screw shaft 41, a ball screw nut 42, a plurality of balls 43, a sector shaft 44 which is an output shaft, and a sector gear 45 are provided.

[0015] The ball screw shaft 41 is rotatably supported by the housing 40 via two bearings 46, 47. A first end of the ball screw shaft 41 passes through the housing 40 and is exposed to the outside. The first end of the ball screw shaft 41 is connected to the steering wheel 24 via the steering shaft 21. A second end of the ball screw shaft 41 opposite the steering wheel 24 is connected to the reducer 25.

[0016] The ball screw nut 42 is screwed onto the ball screw shaft 41 via a plurality of circulable balls 43. Rack teeth 42A are provided on the outer circumferential surface of the ball screw nut 42 so as to be aligned in the axial direction of the ball screw nut 42.

[0017] The sector shaft 44 extends in a direction perpendicular to the axis of the ball screw nut 42 (a direction perpendicular to the plane of the paper in FIG. 2). The sector shaft 44 is rotatably supported in the housing 40 via a bearing (not shown). The sector shaft 44 has an outer end that penetrates the housing 40 and is exposed to the outside. The base end of the pitman arm 31 is fixed to the outer end of the sector shaft 44.

[0018] The sector gear 45 is provided so as to be rotatable integrally with the sector shaft 44. The sector gear 45 is a sector-shaped gear and has a plurality of teeth 45A. The teeth 45A of the sector gear 45 mesh with the rack teeth 42A of the ball screw nut 42.

[0019] The rotation of the steering wheel 24 is transmitted to the ball screw shaft 41 via the steering shaft 21. As the ball screw shaft 41 rotates, the ball screw nut 42 moves in the axial direction relative to the ball screw shaft 41. This causes the sector gear 45 to swing around the sector shaft 44. As the sector gear 45 swings, the sector shaft 44 rotates, causing the pitman arm 31 to swing around the sector shaft 44.

[0020] <Reducer> As shown in FIG. 2, the reducer 25 has a housing 50. The housing 50 is connected to the housing 40 of the steering gearbox 22. The interiors of these housings 40, 50 are in communication with each other. The motor 23 is attached to the exterior of the housing 50. The output shaft 23A of the motor 23 extends in a direction perpendicular to the axis of the ball screw shaft 41 and parallel to the axis of the sector shaft 44. The output shaft 23A of the motor 23 is inserted into the housing 50, passing through it.

[0021] A shaft 51, a worm wheel 52, and a worm 53 are provided inside the housing 50. The shaft 51 is rotatably supported relative to the housing 50 via two bearings 54, 55. A first end of the shaft 51 is connected to a second end of the ball screw shaft 41 so as to be rotatable together. A gap is provided between the second end of the shaft 51 and the housing 50. The worm wheel 52 is provided so as to be rotatable together with the shaft 51. The worm 53 is provided so as to be rotatable together with the output shaft 23A of the motor 23. The axis of the output shaft 23A and the axis of the worm 53 coincide with each other. The worm 53 meshes with the worm wheel 52.

[0022] The torque of the motor 23 is transmitted to the ball screw shaft 41 via the reducer 25. The torque applied to the ball screw shaft 41 in the same direction as the steering direction of the steering wheel 24 assists the steering of the steering wheel 24.

[0023] <Steering control device> As shown in FIG. 3, the electric power steering device 20 has a steering control device 60. The steering control device 60 controls the motor 23 based on the detection results of sensors. The sensors include a torque sensor 61 and a rotation angle sensor 62. The torque sensor 61 is provided on the steering shaft 21. The torque sensor 61 detects the steering torque T applied to the steering shaft 21 via the steering wheel 24. hThe rotation angle sensor 62 is provided on the motor 23. The rotation angle sensor 62 detects the rotation angle θ of the motor 23. m The steering control device 60 detects the steering torque T h , and the rotation angle θ detected by the rotation angle sensor 62 m Based on this, the power supply to the motor 23 is controlled.

[0024] The vehicle 10 may have a driving assistance function to improve safety or convenience, or an automatic driving function in which a system takes over driving. In this case, the vehicle 10 has a host control device 70. The host control device 70 controls the control devices of various on-board systems, including the electric power steering device 20. The host control device 70 determines the optimal control method based on the vehicle's current state, and issues individual control commands to the various control devices according to the desired control method.

[0025] The host controller 70 intervenes in the steering control by the steering control device 60. The host controller 70 switches the automatic driving function between on and off based on the operation of a switch provided in the driver's seat, for example. The automatic driving function also includes a driving assistance function.

[0026] When the automatic driving function is turned on, the upper control device 70 sets a target angle θ * The host control device 70 calculates the target angle θ * The surrounding environment of the vehicle is detected, for example, through a camera. The position (latitude, longitude) of the vehicle is detected based on positioning signals from artificial satellites for the GPS (Global Positioning System).

[0027] Target angle θ * is, for example, the steering angle θ of the steering wheel 24. s The steering control device 60 uses the target angle θ calculated by the higher-level control device 70. *The motor 23 and the steering shaft 21 are connected to each other via a steering gear box 22 and a reducer 25. Therefore, the rotation angle θ of the motor 23 is m and steering angle θ s By utilizing this correlation, the rotation angle θ of the motor 23 is m from steering angle θ s The steering control device 60 calculates the rotation angle θ of the motor 23. m The steering angle θ is calculated based on s and target angle θ * The difference between these values ​​is calculated, and the power supply to the motor 23 is controlled so as to eliminate this difference.

[0028] <Vehicle behavior depending on the load status> As shown in Figure 4, the vehicle 10 is, for example, a freight truck having an article loading facility 10A. The value of the vertical load F1 applied to the vehicle body changes depending on the state of the article loaded. As described above, the vehicle 10 has an axle-suspended suspension 11 (see Figure 1). The amount of deflection of the leaf spring 14 of the suspension 11 changes depending on the state of the article loaded.

[0029] 5, the vertical position of the body frame 16 changes depending on the amount of deflection of the leaf springs 14. For example, the greater the load of goods, i.e., the greater the value of the vertical load F1 applied to the body, the greater the amount of deflection of the leaf springs 14. The body frame 16 sinks downward depending on the amount of deflection of the leaf springs 14.

[0030] The steering gear box 22 is mounted on the body frame 16. Therefore, the vertical position of the steering gear box 22 changes in response to a change in the vertical position of the body frame 16. Therefore, the following concerns arise in the vehicle 10. That is, since the pitman arm 31 and the steered wheels 13 are connected by the link mechanism 30, the steering position of the steered wheels 13 (the steering angle θ w ) changes.

[0031] When the knuckle arm 34 is connected to the steered wheels 13 at a position behind the knuckle spindle, the steering angle θ of the steered wheels 13 w changes to the right side of the steering neutral position as the steering gear box 22 descends. The knuckle spindle is a short shaft for mounting the wheels. When the knuckle arm 34 is connected to the steered wheels 13 at a position forward of the knuckle spindle, the steering angle θ of the steered wheels 13 w changes to the left side with respect to the neutral steering position as the steering gear box 22 descends. The vehicle 10 of this embodiment is the former.

[0032] Therefore, the steering angle θ of the steering wheel 24 changes depending on the load condition of the vehicle 10. s and the steering angle θ of the steering wheel 13 w Therefore, for example, during execution of automatic driving control, the relationship between the target angle θ * The steering angle θ according to w There is a concern that the same phenomenon may occur when the vehicle 10 is accelerating or decelerating.

[0033] Therefore, in this embodiment, the steering control device 60 is configured as follows. <Detailed configuration of steering control device> As shown in Fig. 6, the steering control device 60 has a microcomputer 60A and a drive circuit 60B. The drive circuit 60B receives a current command value I * The motor 23 is supplied with driving power according to the above.

[0034] The microcomputer 60A includes an assist control amount calculation unit 71, a correction amount calculation unit 72, a first adder 73, a steering angle calculation unit 74, an automatic driving control amount calculation unit 75, and a second adder 76. These calculation units are functional parts realized by the CPU (Central Processing Unit) of the microcomputer 60A executing a control program. The microcomputer 60A includes a memory for storing the control program. The memory includes computer-readable media such as RAM (Random Access Memory) and ROM (Read Only Memory). However, realizing each calculation unit by software is merely an example, and at least some of the calculation units may be realized by hardware such as a logic circuit. That is, the steering control device 60 may be configured as a processing circuit including (1) one or more processors that operate according to a computer program (software), (2) one or more dedicated hardware circuits that execute at least some of the various processes, or (3) a combination thereof. The upper control device 70 may also be configured as a processing circuit having a configuration similar to that of the steering control device 60.

[0035] The assist control amount calculation unit 71 calculates the steering torque T h Based on the assist control amount I1 * Assist control amount I1 * is applied to the motor 23 with a steering torque T h The assist control amount calculation unit 71 calculates the amount of current to be supplied to the motor 23 in order to generate an assist torque corresponding to the steering torque T h The larger the absolute value of the assist control amount I1, the larger the absolute value of the assist control amount I1 * The assist control amount calculation unit 71 corresponds to a first calculation unit or a first calculation circuit. * corresponds to the first control amount.

[0036] The correction amount calculation unit 72 operates only while the automatic driving function is on. The correction amount calculation unit 72 calculates the target angle θ *The correction angle θ is the amount of correction for c The correction amount calculation unit 72 calculates the correction map M c Using the correction angle θ c Correction map M c is stored in the storage unit 72A of the correction amount calculation unit 72.

[0037] As shown in the graph in Figure 7, the correction map M c The horizontal axis represents the sinking amount L1 of the body frame 16, and the vertical axis represents the correction angle θ c The map has the following characteristics: the greater the sinking amount L1 of the body frame 16, the greater the correction angle θ c The absolute value of the steering angle θ is set to a larger value. w This is because the amount of change in increases.

[0038] However, the steering angle θ by which the steering wheel 13 is steered according to the load state of the goods is w From the viewpoint of canceling out the correction angle θ c The steering angle θ corresponding to the sinking amount L1 of the body frame 16 is w In this embodiment, the steering angle of the steered wheels 13 changes to the right with respect to the neutral steering position as a reference as the steering gear box 22 descends. For this reason, for example, when the right steering direction with respect to the neutral steering position as a reference is positive and the left steering direction as a negative, the correction angle θ c is given a negative sign.

[0039] Correction Map M c is set by an experiment using an actual vehicle or a computer simulation, for example, in the following steps (A1) and (A2). (A1) First, the relationship between the load state of the vehicle 10 and the amount of sinking L1 of the body frame 16 is grasped. For example, when the load amount of goods is changed in increments of unit load amount within a range from 0 to the maximum load amount while the steering position of the steered wheels 13 is maintained in the steering neutral position, the amount of sinking L1 for each load amount of goods is detected. The steering neutral position is the steering position of the steered wheels 13 that corresponds to the straight-ahead state of the vehicle 10. The amount of sinking L1 is the amount of displacement of the body frame 16 relative to the position of the body frame 16 when the load amount of goods is 0. The amount of displacement of the body frame 16 is the amount of change in the position of the steering gear box 22 on the body frame 16 at its mounting position.

[0040] (A2) Next, the steering angle θ for the sinking amount L1 for each load of goods w The amount of change in the steering angle θ relative to the amount of sinking L1 is determined. w The amount of change in the steering angle θ is determined by the mechanical constraints imposed on the steered wheels 13 by the link mechanism 30. w The amount of change in the steering angle θ w The amount of sinking L1 and the steering angle θ for each load of goods w From the relationship with the change in the steering angle θ w is set to an angle corresponding to the straight-ahead state of the vehicle 10 (for example, a steering angle θ w = 0°) w The correction amount for each load amount can be calculated. w and steering angle θ s Since there is a correlation between the steering angle θ w From the correction amount, the steering angle θ w to an angle corresponding to the straight-ahead state of the vehicle 10. s The correction angle θ is the amount of correction c can be calculated for each load of goods.

[0041] As shown in Fig. 6, the correction amount calculation unit 72 monitors the actual loading state of the vehicle 10. The correction amount calculation unit 72 recognizes the loading state of goods based on the amount of sinking L1 of the body frame 16 detected by an on-board sensor 63. The sensor 63 is, for example, a vehicle height sensor that detects the movement of the suspension 11, and is provided on each of the front, rear, left and right wheels of the vehicle including the steered wheels 13. The correction amount calculation unit 72 calculates a correction map M shown in the graph of Fig. 7 based on the amount of sinking L1 of the body frame 16 detected by the sensor 63. c Using the correction angle θ c The amount of sinking L1 of the body frame 16 is a state variable that reflects the vehicle attitude. The correction amount calculation unit 72 corresponds to a third calculation unit or a third calculation circuit.

[0042] The first adder 73 calculates the target angle θ * and the correction angle θ calculated by the correction amount calculation unit 72. c By adding these, the final target angle θ f * Calculate the following.

[0043] The steering angle calculation unit 74 calculates the rotation angle θ of the motor 23 detected by the rotation angle sensor 62. m The steering angle θ, which is the rotation angle of the steering wheel 24, is calculated based on the s The steering angle calculation unit 74 calculates the rotation angle θ of multiple rotations exceeding 360° by counting the number of rotations of the motor 23, for example, with reference to the steering neutral position of the steering wheel 24, which corresponds to the straight-ahead state of the vehicle. m The steering angle calculation unit 74 calculates the absolute value of the rotation angle θ of the motor 23 by converting a conversion coefficient based on the reduction ratio between the motor 23 and the steering shaft 21. m By multiplying this, the steering angle θ s Calculate the following.

[0044] The automatic driving control amount calculation unit 75 operates only while the automatic driving function is turned on. The automatic driving control amount calculation unit 75 calculates the final target angle θ f *, and the steering angle θ of the steering wheel 24 calculated by the steering angle calculation unit 74. s The automatic driving control amount calculation unit 75 takes in the steering angle θ s The final target angle θ f * The automatic driving control amount I2 is achieved by executing feedback control to follow the * The automatic driving control amount calculation unit 75 calculates, for example, the final target angle θ f * and the steering angle θ calculated by the steering angle calculation unit 74 s Deviation Δθ(=θ f * -θ s ) is calculated, and the calculated deviation Δθ is subjected to proportional, integral and differential calculations to obtain the automatic driving control amount I2 * That is, the automatic driving control amount I2 * is the sum of the output value of the proportional element with the deviation Δθ as input, the output value of the integral element with the deviation Δθ as input, and the output value of the differential element with the deviation Δθ as input. * is the steering angle θ calculated by the steering angle calculation unit 74 s The final target angle θ f * The automatic driving control amount I2 indicates the amount of current that should be supplied to the motor 23 to make it follow the automatic driving control amount I2. The automatic driving control amount calculation unit 75 corresponds to the second calculation unit or the second calculation circuit. * corresponds to the second control amount.

[0045] The second adder 76 calculates the assist control amount I1 * and automatic driving control amount I2 * By adding these, the current command value I * Calculate the following. <Operation of the embodiment> Next, the operation of this embodiment will be described.

[0046] First, the target angle θ calculated by the upper control device 70 * Let us consider the case where the correction is not performed. As shown in FIG. 8, for example, the target angle θ *is the angle (θ s =0°), the steering wheel 13 is turned to the right at an angle Δθ w That is, the target angle θ * The steering angle θ according to w Therefore, even if the rotational position of the steering wheel 24 is controlled to a neutral steering position corresponding to the straight-ahead state of the vehicle 10, the vehicle 10 will not move in a straight line. In other words, the vehicle 10 will move in the direction in which the steered wheels 13 are displaced depending on the load state of the goods.

[0047] In this embodiment, the steering angle θ of the steered wheels 13 is adjusted according to the load state of the goods. w Specifically, the target angle θ * Correction angle θ according to the loading condition of the goods c is added. Correction angle θ c is the steering angle θ by which the steering wheel 13 is displaced depending on the load state of the goods. w It is set based on the viewpoint of canceling out.

[0048] For example, as shown in Figure 8, the target angle θ * is an angle corresponding to the vehicle 10 traveling straight, the steered wheels 13 are turned to the right at an angle Δθ w When the steering wheel 13 is displaced by an angle Δθ w Correction angle θ to turn the steering wheel by c is the target angle θ * This results in the final target angle θ f * The steering angle θ of the steering wheel 24 is calculated. s is the final target angle θ f * By controlling the steering angle θ of the steered wheels 13 w is the original target angle θ calculated by the upper control device 70 * The steering angle θ according to w is corrected to.

[0049] <Effects of the embodiment> According to this embodiment, the following effects can be obtained. (1) The steering control device 60 detects the amount of sinking L1 of the body frame 16, which indicates one of the vehicle postures, and the steering angle θ w Based on the correlation between the change in the steering angle θ and the amount of sinking L1 of the body frame 16 detected by the on-board sensor 63, w Therefore, the motor 23 is controlled so as to correct the change in the steering angle θ w This in turn reduces the influence on the behavior of the vehicle 10.

[0050] (2) The amount of sinking L1 of the body frame 16 changes depending on the load state of the goods or the traveling state of the vehicle 10. The steering angle θ w Therefore, the change in the steering angle θ w The influence of the load state of the goods or the running state of the vehicle 10 on the load can be suppressed.

[0051] (3) When the host controller 70 intervenes in the steering control, the steering control device 60 determines the steering angle θ according to the amount of sinking L1 of the body frame 16 detected by the sensor 63. w The target angle θ * Correction angle θ c Calculate the target angle θ * For example, the steering angle θ s The target angle θ * Correction angle θ c By reflecting this, the final target angle θ f * The final target angle θ f * Actual steering angle θ s By controlling the motor 23 so that the amount of sinking L1 of the body frame 16 follows the steering angle θ w Therefore, the target angle θ calculated by the upper control device 70 can be reduced. * A steering operation according to the above can be obtained.

[0052] (4) The steering control device 60 generates a correction map M that defines the relationship between the sinking amount L1 of the body frame 16 and the correction angle θ1. c Correction map M c By using the above, the correction angle θ c can be easily found.

[0053] <Other embodiments> This embodiment may be modified as follows. The correction amount calculation unit 72 may be configured to operate even when the automatic driving function is turned off. In this case, as shown by the two-dot chain line in FIG. 1, the correction amount calculation unit 72 calculates the correction control amount I according to the load state of the goods while the automatic driving function is turned off. c Calculate the corrected control amount I c is the steering angle θ by which the steering wheel 13 is displaced depending on the load state of the goods. w The correction control amount I is the amount of current that should be supplied to the motor 23 to cancel out c The absolute value of the assist control amount I1 is set to a larger value as the sinking amount L1 of the body frame 16 increases. * and correction control amount I c By adding these, the current command value I * Calculate the corrected control amount I c The current command value I * The driving of the motor 23 is controlled based on the steering angle θ of the steering wheel 24. s and the steering angle θ of the steering wheel 13 w Therefore, even when the upper control device 70 does not intervene in the steering control, the sinking amount L1 of the body frame 16 is maintained in accordance with the steering angle θ w This in turn reduces the influence on the behavior of the vehicle 10.

[0054] The correction amount calculation unit 72 may recognize the load condition of goods based on the pitching motion of the vehicle 10. Pitching motion is a rotational motion around an axis in the left-right direction relative to the traveling direction of the vehicle body. For example, when the brake is applied, the vehicle body leans forward, and when the brake is released, the rear of the vehicle body sinks in reaction. Pitching motion is also caused by unevenness in the road surface. The pitch angle changes with pitching motion. The pitch angle is the angle at which the vehicle body tilts around an axis in the left-right direction relative to the traveling direction of the vehicle body. The pitch angle also changes depending on the load condition of goods. As the load of goods increases, the amount of sinking L1 of the body frame 16 increases, and therefore the pitch angle tends to become larger. The correction amount calculation unit 72 calculates a correction angle θ according to the pitch angle detected by a pitch angle sensor mounted on the vehicle. c Or correction control amount I c Calculate the following.

[0055] A steering sensor may be mounted on the steering shaft 21. The steering sensor detects the steering angle θ of the steering wheel 24. s In this case, the automatic driving control amount calculation unit 75 detects the steering angle θ s Using automatic driving control amount I2 * The following may be calculated.

[0056] The target angle θ calculated by the upper control device 70 * may be the target rotation angle of the motor 23. In this case, the correction amount calculation unit 72 calculates a correction angle θ for the target rotation angle of the motor 23 based on the sinking amount L1 of the body frame 16 detected by the sensor 63. c The correction amount calculation unit 72 calculates the amount of sinking L1 of the body frame 16 and the correction angle θ for the target rotation angle of the motor 23. c The correction map that defines the relationship between the absolute value of the correction angle θ and the target rotation angle of the motor 23 is used. c The first adder 73 calculates the target rotation angle of the motor 23 calculated by the upper control device 70 and the correction angle θ calculated by the correction amount calculation unit 72. cThe automatic driving control amount calculation unit 75 calculates the final target rotation angle of the motor 23 by adding the rotation angle θ m The automatic driving control amount I2 is calculated by executing feedback control to make the motor 23 follow the final target rotation angle. * Calculate the following.

[0057] The target angle θ calculated by the upper control device 70 * may be the target steering angle of the steered wheels 13. In this case, the correction amount calculation unit 72 calculates a correction angle θ for the target steering angle of the steered wheels 13 based on the sinking amount L1 of the body frame 16 detected by the sensor 63. c The correction amount calculation unit 72 calculates the amount of sinking L1 of the body frame 16 and the correction angle θ c A correction map that defines the relationship between the absolute value of the correction angle θ c The first adder 73 calculates the target steering angle calculated by the upper control device 70 and the correction angle θ calculated by the correction amount calculation unit 72. c The automatic driving control amount calculation unit 75 calculates the final target steering angle by adding the rotation angle θ m The actual steering angle θ calculated based on w The automatic driving control amount I2 is calculated by executing feedback control that makes the * Calculate the following.

[0058] The vehicle 10 may have an independent suspension that supports each wheel independently. In this case, the type of steering gearbox 22 is not limited to the RBS type. The steering gearbox 22 may be, for example, a rack-and-pinion type steering gearbox. For example, when the vehicle 10 travels around a curve, the suspension that supports at least one of the left and right steerable wheels 13 sinks relative to the steerable wheels 13 due to the inertial force, and the steering angle θ of the steerable wheels 13 changes. w As in the previous embodiment, the steering angle θw By correcting the change in the steering angle θ of the suspension supporting the steered wheels 13, w The impact on the

Claims

1. An electric power steering device that applies torque to a steering mechanism of a vehicle, The vehicle is configured such that the steering angle of the steered wheels changes depending on the vehicle attitude, The electric power steering device includes: a motor configured to generate the torque; a steering control device configured to control the motor in accordance with a steering state, The steering control device is an electric power steering device configured to control the motor to correct the change in the steering angle in accordance with the vehicle attitude detected through an on-board sensor, based on the correlation between the vehicle attitude and the change in the steering angle.

2. The steering control device includes a first calculation unit configured to calculate a first control amount for causing the motor to generate the torque in accordance with a steering state of a steering wheel; a second calculation unit configured to calculate a second control amount for causing an actual steering angle to follow a target angle, which is a target value of the steering angle of the steering wheel generated when an on-board higher-level control device intervenes in steering control; and and a third calculation unit configured to calculate a correction angle for the target angle based on the vehicle attitude detected through the sensor when the higher-level control device intervenes in steering control, in order to correct a change in the steering angle according to the vehicle attitude.

3. 3. The electric power steering device according to claim 2, wherein the steering control device is configured to calculate a correction control amount for the first control amount based on the vehicle attitude detected through the sensor when the higher-level control device does not intervene in the steering control, in order to correct a change in the steering angle according to the vehicle attitude.

4. 4. The electric power steering device according to claim 2, wherein the steering control device has a correction map that defines the relationship between the vehicle attitude and the correction angle.

5. the vehicle has an article loading facility on which articles are loaded, and a body frame whose vertical position changes depending on the state of the article loaded, and is configured so that the steering angle changes depending on the change in the vertical position of the body frame, 5. The electric power steering device according to claim 1, wherein the sensor is configured to detect a change in the vertical position of the body frame as the vehicle attitude.

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