Steering assist device, steering assist method, and vehicle

Abstract

The present application provides a steering assist device that reduces the force required for steering while maintaining the straight-ahead stability of a vehicle. The steering assist device assists in steering a vehicle having a kingpin offset, the steering assist device including a detection unit that detects a steering angle of a steering wheel, and an assist unit that changes a running torque based on an assist torque, the assist torque being greater the greater the steering angle when the steering angle is greater than or equal to a threshold value, and the assist torque being a value less than or equal to a minimum value of the assist torque when the steering angle is less than the threshold value, the assist unit decreasing a running torque of a first motor that drives a steering wheel on an inside of a turn of the vehicle by an amount of the assist torque and increasing a running torque of a second motor that drives a steering wheel on an outside of the turn of the vehicle by the amount of the assist torque during an increase in the steering angle.

Description

Technical Field

[0001] This disclosure relates to steering assist devices, steering assist methods, and vehicles. Background Technology

[0002] In recent years, in-wheel-motorvehicles capable of independently driving multiple wheels have been developed (e.g., Patent Document 1), in which a hub motor is provided for each drive wheel.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent document 1: Japanese Patent Application Publication No. 2014-23199. Summary of the Invention

[0006] The problem the invention aims to solve

[0007] In most in-wheel electric locomotives, the in-wheel motor is located inside the drive wheel. Therefore, the steering knuckle, which holds the wheel in place and through which the wheel's rotation centerline passes during steering, is positioned away from the wheel. In this situation, a distance known as kingpin offset easily arises between the point where the rotation centerline intersects the ground and the wheel's contact point. A larger kingpin offset requires more force to steer the vehicle, resulting in a heavier steering wheel for the driver.

[0008] In addition, in general vehicles, the caster angle is set to a certain size (e.g., about 2 degrees) to improve straight-line stability. However, the larger the caster angle, the greater the force required to steer the vehicle.

[0009] Therefore, in vehicles with kingpin offset, if the caster angle is set to the same level as in conventional vehicles, the force required for steering becomes greater. On the other hand, if the caster angle is made closer to 0 degrees, the force required for steering can be reduced to some extent, but the vehicle's straight-line stability will decrease.

[0010] The purpose of this disclosure is to provide a steering assist device, steering assist method, and vehicle that reduces the force required for steering control while maintaining the straight-line stability of the vehicle.

[0011] Solution to the problem

[0012] One aspect of the steering assist device disclosed herein is a steering assist device for assisting steering operation of a vehicle having a kingpin offset. This steering assist device includes: a detection unit for detecting the steering angle of the steering wheel; and an assist unit that varies the driving torque based on an assist torque. When the steering angle is above a threshold, the larger the steering angle, the greater the assist torque; and when the steering angle is below the threshold, the assist torque is a value below the minimum value of the assist torque when the steering angle is above the threshold. During the period when the steering angle is increasing, the assist unit reduces the driving torque of a first motor by the amount of the assist torque and increases the driving torque of a second motor by the amount of the assist torque. The first motor is a motor that drives the steering wheel on the inside of the vehicle's turning radius, and the second motor is a motor that drives the steering wheel on the outside of the vehicle's turning radius.

[0013] One aspect of the steering assistance method disclosed herein is a steering assistance method for assisting the steering of a vehicle having a kingpin offset. This steering assistance method includes the following steps: detecting the steering angle of the steering wheel; and, during the period when the steering angle is increasing, based on an assistance torque, decreasing the driving torque of a first motor by the amount of the assistance torque and increasing the driving torque of a second motor by the amount of the assistance torque, wherein when the steering angle is above a threshold, the larger the steering angle, the greater the assistance torque; and when the steering angle is below the threshold, the assistance torque is a value below the minimum value of the assistance torque when the steering angle is above the threshold. The first motor is a motor that drives the steering wheel on the inside of the vehicle's turning radius, and the second motor is a motor that drives the steering wheel on the outside of the vehicle's turning radius.

[0014] One embodiment of the vehicle disclosed herein has the aforementioned steering assistance device.

[0015] Invention Effects

[0016] According to this disclosure, a steering assist device can be provided that reduces the force required for steering operation while maintaining the straight-line stability of the vehicle. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the vehicle used in the implementation method.

[0018] Figure 2 This is a block diagram illustrating the functional structure of the vehicle in the implementation method.

[0019] Figure 3 This is a schematic diagram illustrating the kingpin offset of a vehicle used to explain the implementation method.

[0020] Figure 4AThis is a diagram used to illustrate the caster angle of a typical vehicle. Figure 4B This is a schematic diagram illustrating the rearward tilt angle of the vehicle used to explain the implementation method.

[0021] Figure 5 This is a flowchart illustrating the control processing performed by the steering assist device in the implementation of the method.

[0022] Figure 6 This is a schematic diagram illustrating a scenario where a vehicle makes a left turn according to the implementation method.

[0023] Figure 7 This is a diagram illustrating the amount of assistance provided by the steering assist device in the implementation of the method.

[0024] Figure 8 This is a diagram illustrating the driving torque of the left and right motors when the vehicle transitions from a straight-line state to a turning state in an embodiment.

[0025] Figure 9 This is a diagram illustrating the driving torque of the left and right motors when the vehicle transitions from a turning state to a straight-line state, as described in the embodiment.

[0026] Figure 10 This is a diagram illustrating the coefficients of the steering assist device in the modified example. Detailed Implementation

[0027] (Implementation Method)

[0028] The embodiments of this disclosure will now be described with reference to the accompanying drawings.

[0029] First, refer to Figures 1-2 The structure of the vehicle 1 equipped with the steering assist device of this embodiment will be described. Figure 1 This is a schematic diagram of vehicle 1 in this embodiment. Figure 2 This is a block diagram illustrating the functional structure of vehicle 1 according to this embodiment. It should be noted that vehicle 1 in this embodiment is a hub locomotive with the left and right front wheels as steering wheels.

[0030] Vehicle 1 is equipped with: multiple steering wheels 11 and 12, multiple motors 21 and 22, and multiple inverters 23 and 24 (see reference). Figure 2 ), multiple steering knuckles 31, 32, steering control device 70, steering angle sensor 80, and ECU (Electronic Control Unit) 100 (see reference) Figure 2 ).

[0031] Steering wheels 11 and 12 are the left and right front wheels, respectively. When steering, they rotate around the center line of rotation, i.e., the kingpin L1 (see reference). Figure 3 Rotate.

[0032] Motors 21 and 22 are hub motors used for driving. Motors 21 and 22 are respectively inserted inside the steering wheels 11 and 12, and connected to inverters 23 and 24 (see reference). Figure 2 The electricity generated by the motors 21 and 22 accordingly produces a driving torque and drives the steering wheels 11 and 12 independently. It should be noted that the driving torque is the torque output by the motors 21 and 22 for the driving of the vehicle 1. In this specification, the steering wheels 11 and 12 are sometimes referred to as "left steering wheel 11" and "right steering wheel 12", respectively, and the motors 21 and 22 are referred to as "left motor 21" and "right motor 22", respectively.

[0033] Inverters 23 and 24 (refer to) Figure 2 Under the control of ECU100, power is supplied to motors 21 and 22.

[0034] Steering knuckles 31 and 32 are components that hold steering wheels 11 and 12 and are located between steering wheels 11 and 12 and steering control device 70.

[0035] The steering tie rods 41 and 42 are components that connect the steering knuckles 31 and 32 to the steering control device 70.

[0036] Steering control device 70 operates by causing steering wheels 11 and 12 to rotate around the kingpin L1 (see reference). Figure 3 A device for steering vehicle 1 by rotation. Figure 1 The steering control device 70 is a rack and pinion type steering control device, which includes: a steering wheel 60, a steering shaft 61, a pinion component 62, and a rack shaft 63.

[0037] Steering wheel 60 is, for example, a steering wheel. The driver can input steering instructions to steering control device 70 by rotating steering wheel 60.

[0038] The steering shaft 61 is a component whose one end is connected to the steering wheel 60 and the other end is connected to the pinion assembly 62.

[0039] The pinion component 62 is a component in which a pinion is formed.

[0040] A rack is formed on the rack shaft 63, and the rack shaft 63 is configured such that one end of its rack shaft 63 is connected to the steering tie rods 41 and 42 respectively, and the rack meshes with the pinion of the pinion component 62.

[0041] The driver rotates the steering wheel 60, causing the steering shaft 61 and pinion assembly 62 to rotate. This rotational motion is converted into a reciprocating motion of the rack shaft 63 in the vehicle width direction. This reciprocating motion is transmitted to the steering knuckles 31 and 32 via the steering tie rods 41 and 42, thereby causing the steering wheels 11 and 12 to rotate around the left and right kingpins L1, respectively.

[0042] Steering angle sensor 80 is disposed on steering shaft 61, detects the rotation angle of steering shaft 61, and outputs the rotation angle information and rotation speed information to ECU 100. It should be noted that in this embodiment, the rotation angle of steering shaft 61 is the same as the rotation angle of steering wheel 60. Therefore, it can be considered that steering angle sensor 80 actually detects the rotation angle of steering wheel 60.

[0043] It should be noted that in the following description, the rotation angle of the steering wheel 60 may sometimes be simply referred to as the "rotation angle", and the term "steering angle" may sometimes be used as the absolute value of the rotation angle.

[0044] Furthermore, in this instruction manual, the rotation angle of the steering wheel 60 when the vehicle 1 is moving straight is set to 0 degrees, and the direction in which the steering wheel 60 is rotated to turn the vehicle 1 to the right is specified (see reference). Figure 1 The arrow is defined as the positive direction. Thus, for example, if the steering wheel 60 is rotated 30 degrees in the positive direction from a state of 0 degrees rotation angle, the rotation angle is "+30 degrees", and if it is rotated 30 degrees in the negative direction, the rotation angle is "-30 degrees".

[0045] ECU100 performs overall control of vehicle 1. ECU100 is a microprocessor equipped with CPU (Central Processing Unit), ROM (Read Only Memory), and RAM (Random Access Memory).

[0046] In this embodiment, the ECU 100 functions as a steering assist device. That is, the ECU 100 reads a predetermined program stored in the ROM through the CPU, expands it in the RAM, and executes the expanded predetermined program, thereby functioning as the detection unit 101 and the assist unit 102.

[0047] The detection unit 101 detects the rotation angle and angular velocity of the steering wheel 60 based on the rotation angle and rotation speed information from the steering angle sensor 80.

[0048] Therefore, the detection unit 101 is able to detect the rotation operation of the steering wheel 60 (hereinafter referred to as "steering operation"). The steering operation includes the operation of increasing the steering angle and the operation of decreasing the steering angle. The operation of increasing the steering angle is the operation of rotating the steering wheel 60 in a way that causes the vehicle 1 to change from a straight-moving state (hereinafter sometimes referred to as "straight-moving state") to a state of turning left or right (hereinafter sometimes referred to as "turning state"). The operation of decreasing the steering angle is the operation of rotating the steering wheel 60 in a way that causes the vehicle 1 to change from a turning state to a straight-moving state.

[0049] Based on the detection results from the detection unit 101, the auxiliary unit 102 outputs control signals to the inverters 23 and 24 to change the driving torque of the motors 21 and 22. Thus, the auxiliary unit 102 assists in the steering control of the vehicle 1. In addition to assisting in the steering control of the vehicle 1, the auxiliary unit 102 also performs processing to demonstrate the straight-line stability of the vehicle 1. The assistance performed by the auxiliary unit 102 and the processing to demonstrate straight-line stability, other than assistance, will be explained in detail later.

[0050] <Kingpin Offset Distance>

[0051] Next, refer to Figure 3 The kingpin offset of vehicle 1 is explained. Figure 3 This is a schematic diagram illustrating the kingpin offset R of vehicle 1, showing the area near the steering wheel 12 when viewed from the rear. It should be noted that... Figure 3 P1 is the point where the main pin L1 intersects with the ground, P2 is the grounding center point of the steering wheel 12, and L2 is the perpendicular line passing through the grounding center point P2.

[0052] In a typical vehicle, the kingpin L1 is tilted in the direction of vehicle width, so that the distance between point P1 and the ground center point P2, i.e. the kingpin offset R, is close to zero, thereby reducing the force required to rotate the steering wheel 60.

[0053] In this embodiment, motors 21 and 22 are disposed inside the steering wheels 11 and 12. Therefore, steering knuckles 31 and 32 are disposed outside the steering wheels 11 and 12, specifically disposed at a position further inside in the vehicle width direction than the motors 21 and 22. As a result, steering knuckles 31 and 32 are disposed at a position away from the ground center point P2 of the steering wheels 11 and 12.

[0054] The left and right kingpins L1 pass through the steering knuckles 31 and 32, respectively. Therefore, in vehicle 1 where the steering knuckles 31 and 32 are away from the ground center point P2, if an attempt is made to make the kingpin offset R zero, the tilt angle of the kingpin L1 in the vehicle width direction (called the "kingpin angle") will become very large. As a result, when the steering angle of the steering wheel 60 is large, an undesirable situation occurs where the force required for steering becomes larger.

[0055] Vehicle 1 in this embodiment is as follows Figure 3 As shown, the kingpin shaft L1 is perpendicular to the ground, that is, the kingpin angle is set to 0 degrees.

[0056] <Lean Angle>

[0057] Next, refer to Figure 4A and Figure 4B The caster angle of vehicle 1 will be explained. Figure 4A This is a schematic diagram used to illustrate the caster angle α of a typical vehicle. Figure 4B This is a schematic diagram illustrating the rearward tilt angle α of vehicle 1 in this embodiment. Figure 4A L3 is the vertical line relative to the ground, 212 is the steering wheel of a typical vehicle, and 232 is the steering knuckle of a typical vehicle. Figure 4A and Figure 4B Both are shown near the steering control wheels 212 and 12 when viewed from the inside in the vehicle width direction.

[0058] In typical vehicles, to improve straight-line stability, the caster angle α is set to be larger than 0 degrees (for example, around 2 degrees) (see reference). Figure 4A ).

[0059] When the caster angle is set greater than 0 degrees, the force required to rotate the steering wheel 60 degrees increases. Therefore, in this embodiment, the caster angle of vehicle 1 when unloaded is set to 0 degrees (see reference). Figure 4B ).

[0060] <Handling of steering assist devices>

[0061] Reference Figure 5 The control processing performed by the ECU (Engine Control Unit) 100 is explained. Figure 5 This is a flowchart representing the control processing performed by the ECU (Engine Control Unit) 100.

[0062] First, the ECU 100 determines whether the vehicle 1 has started moving (step S1). In step S1, the ECU 100 determines that the vehicle 1 has started moving if the motors 21 and 22 are detected to be rotating using the specified sensors, and determines that the vehicle 1 is in a stopped state if the motors 21 and 22 are not detected to be rotating.

[0063] If vehicle 1 has not started driving (No in step S1), ECU 100 terminates control processing.

[0064] When vehicle 1 starts moving ("Yes" in step S1), ECU 100 (detection unit 101) determines whether the steering angle of steering wheel 60 has increased (step S2). Based on the rotation angle information from steering angle sensor 80, ECU 100 (detection unit 101) determines that the steering angle has increased if the steering angle has increased, and determines that the steering angle has not increased if the steering angle has decreased or has not changed.

[0065] It should be noted that, for the case where the steering angle increases, we assume a steering operation that increases the steering angle. For the case where the steering angle decreases, we assume a steering operation that decreases the steering angle. Furthermore, for the case where the steering angle does not change, we assume no steering operation is performed.

[0066] When the steering angle increases (Yes in step S2), ECU100 (auxiliary unit 102) starts the first assistance (step S3).

[0067] In step S3, the ECU 100 (auxiliary unit 102) determines the amount of torque, i.e., the auxiliary torque, that is, the amount by which the driving torque is increased or decreased for the purpose of assistance, based on the steering angle. Furthermore, the ECU 100 (auxiliary unit 102) reduces the driving torque of the motor driving the steering wheel on the inside of the turn of the vehicle 1 by the amount of auxiliary torque, and increases the driving torque of the motor driving the steering wheel on the outside of the turn by the amount of auxiliary torque.

[0068] Next, the ECU 100 (detection unit 101) determines whether the change in steering angle has stopped (step S4). Based on the rotation angle information from the steering angle sensor 80, the ECU 100 (detection unit 101) determines that the change in steering angle has stopped if the steering angle has not changed, and determines that the change in steering angle has not stopped if the steering angle is changing.

[0069] If the change in steering angle does not stop (No in step S4), the ECU 100 (detection unit 101) repeatedly performs the process of step S4 until the change in steering angle stops. If the change in steering angle has stopped (Yes in step S4), the ECU 100 (assistance unit 102) ends the first assistance (step S5). Afterwards, the ECU 100 executes the process of step S10.

[0070] If the steering angle does not increase (No in step S2), ECU100 determines whether the angular velocity of the steering wheel 60 is above the set value (step S6). The set value will be explained below.

[0071] In vehicles with a caster angle other than 0 degrees, when the steering wheel angle is not near 0 degrees, a torque is generated in the steering wheel. The steering wheel receives this torque and tilts from the direction the vehicle is facing when turning to the direction it is facing when the vehicle is going straight. This torque will be referred to as the "self-aligning torque." Furthermore, with the movement of this steering wheel, the steering wheel angle approaches 0 degrees. It should be noted that the larger the caster angle, the greater the self-aligning torque.

[0072] In a vehicle with a caster angle of 0 degrees, no self-centering torque is generated, and the steering wheel will not approach 0 degrees even with a relatively large steering angle. In this embodiment, a virtual caster angle is set, and the self-centering torque to be generated is calculated assuming that the caster angle of vehicle 1 is set to the virtual caster angle. Furthermore, when this self-centering torque is generated, the angular velocity of the steering wheel 60 when it rotates toward a steering angle of 0 degrees is calculated for each steering angle. This calculated value is set as the set value for each steering angle. In this embodiment, the virtual caster angle is set to 2 degrees.

[0073] In step S6, the ECU100 determines whether the angular velocity of the steering wheel 60 is above the set value based on the steering angle and angular velocity of the steering wheel 60.

[0074] If the angular velocity of the steering wheel 60 is less than the set value (No in step S6), the ECU100 executes the processing in step S10.

[0075] When the angular velocity of the steering wheel 60 is above the set value ("Yes" in step S6), the ECU 100 (auxiliary unit 102) starts the second assistance (step S7).

[0076] It should be noted that when the angular velocity of the steering wheel 60 is above a set value, for example, imagine that the driver turns the steering wheel 60 when turning left or right and performs an operation that reduces the steering angle.

[0077] In step S7, the ECU 100 (auxiliary unit 102) determines the auxiliary torque based on the steering angle. Furthermore, the ECU 100 (auxiliary unit 102) increases the driving torque of the motor driving the steering wheel on the inside of the turn of the vehicle 1 by the amount of auxiliary torque, and decreases the driving torque of the motor driving the steering wheel on the outside of the turn by the amount of auxiliary torque.

[0078] Next, the ECU 100 (detection unit 101) determines whether the change in steering angle has stopped (step S8). If the change in steering angle has not stopped (step S8 "No"), the process of step S8 is repeated until the change in steering angle stops. If the change in steering angle has stopped (step S8 "Yes"), the ECU 100 (assistance unit 102) ends the second assistance (step S9). Afterwards, the ECU 100 executes the process of step S10.

[0079] In step S10, the ECU 100 (detection unit 101) determines whether the steering angle is not near 0 degrees based on the rotation angle information from the steering angle sensor 80. Here, "near 0 degrees" refers to a predetermined angle range near 0 degrees, for example, the predetermined angle range is set to be above -2 degrees and below +2 degrees.

[0080] If the steering angle is not near 0 degrees (No in step S10), ECU100 executes the processing in step S14.

[0081] When the steering angle is near 0 degrees ("Yes" in step S10), the ECU100 (auxiliary unit 102) begins steering return control (step S11).

[0082] As described above, in vehicles where the caster angle is not 0 degrees, when the steering wheel angle is not near 0 degrees, the vehicle's steering wheel receives a return torque and tilts towards the direction the vehicle is facing when turning, in a manner that is in the direction the vehicle is facing when it is in a straight line. Consequently, the steering wheel angle approaches 0 degrees.

[0083] Steering return control is used to demonstrate the following motion and rotation control: the motion of the steering wheel from the direction of turning to the direction of straight-line movement, and the rotation of the steering wheel 60 toward a steering angle of 0 degrees.

[0084] Specifically, the ECU 100 (auxiliary unit 102) increases the driving torque of the motor driving the steering wheel on the inside of the turn of the vehicle 1 by a predetermined amount, and decreases the driving torque of the motor driving the steering wheel on the outside of the turn by a predetermined amount. Hereinafter, the predetermined torque for performing steering return control will be referred to as the "return control torque".

[0085] The return control torque is set to the amount required for the steering wheel 60 to rotate towards the steering angle 0 degrees at an angular velocity equivalent to the aforementioned setting, without driver intervention or holding of the steering wheel 60. Therefore, the return control torque varies depending on the steering angle, and the larger the steering angle, the greater the return control torque.

[0086] When steering return control is executed, the steering wheels 11 and 12 move from the orientation of the vehicle 1 when it is turning to the orientation of the vehicle when it is going straight. As a result, a rotational torque is generated on the steering shaft 61 that brings the steering wheel 60 close to the steering angle of 0 degrees. This allows the driver to feel that the vehicle 1 is going straight.

[0087] Next, the ECU100 (detection unit 101) determines whether the steering angle is near 0 degrees (step S12). If the steering angle is not near 0 degrees (no in step S12), the steering return control continues to be executed, and the process of step S12 is repeated until the steering angle drops to near 0 degrees.

[0088] When the steering angle is near 0 degrees (Yes in step S12), the ECU100 (auxiliary unit 102) ends the steering return control (step S13).

[0089] Then, the ECU100 (detection unit 101) determines whether the vehicle 1 has stopped moving (step S14). If the ECU100 detects that the rotation of the motors 21 and 22 has stopped, it determines that the vehicle 1 has stopped moving; if the ECU100 detects that the motors 21 and 22 are rotating, it determines that the vehicle 1 is moving.

[0090] If the vehicle 1 does not stop moving (No in step S14), the ECU 100 executes the processing in step S2. If the vehicle 1 stops moving (Yes in step S14), the ECU 100 ends the control processing.

[0091] It should be noted that, alternatively, if the steering angle increases while steering return control is being executed, the ECU 100 (auxiliary unit 102) may terminate steering return control and execute the first auxiliary function. Alternatively, if the steering angle decreases and the angular velocity of the steering wheel 60 becomes above a set value while steering return control is being executed, the steering return control may terminate and the second auxiliary function may be executed.

[0092] <First Support and Second Support>

[0093] Below, refer to Figures 6-9 The first and second auxiliary systems will be explained using the example of vehicle 1 making a left turn.

[0094] Figure 6 This is a schematic diagram showing vehicle 1 turning left. Figure 7 It is a diagram used to illustrate the auxiliary quantity (auxiliary torque) during steering operation. Figure 8 This diagram illustrates the respective driving torques of the left and right motors 21 and 22 when vehicle 1 transitions from a straight-line state to a turning state. Figure 8 TL and TR are curves representing the driving torque of the left motor 21 and the right motor 22. Figure 8 The TS is the torque that motors 21 and 22 are outputting to make vehicle 1 move, which is independent of auxiliary processing and is determined according to the target speed of vehicle 1. Figure 9 This is a diagram illustrating the driving torques TL and TR of the left and right motors 21 and 22 when vehicle 1 transitions from a turning state to a straight-line state.

[0095] [First Support]

[0096] While driving, if the steering wheel 60 starts to rotate in the negative direction from the 0-degree state (i.e., state 1), the ECU 100 (auxiliary unit 102) determines the auxiliary torque Ta1(θ) and starts the first assistance based on the auxiliary torque Ta1(θ).

[0097] The magnitude of the auxiliary torque Ta1(θ) is determined by the rotation angle θ. For example... Figure 7 As shown, when the steering angle |θ| is above a first threshold (e.g., 270 degrees), the auxiliary torque Ta1(θ) is a predetermined value Tc1 (constant value). Furthermore, when the steering angle |θ| is less than the first threshold but above a second threshold (e.g., 5 degrees), the auxiliary torque Ta1(θ) increases as the steering angle |θ| increases. Moreover, when the steering angle |θ| is less than the second threshold, the auxiliary torque Ta1(θ) is a predetermined value Tc2 (constant value).

[0098] It should be noted that the specified value Tc1 is a value above the maximum value of the auxiliary torque Ta1(θ) when the steering angle |θ| is less than the first threshold and above the second threshold. The specified value Tc2 is a small value below the minimum value of the auxiliary torque Ta1(θ) when the steering angle |θ| is less than the first threshold and above the second threshold. Figure 7 The specified value Tc2 is the same as the minimum value, but it can also be 0, for example.

[0099] The ECU 100 (auxiliary unit 102) determines the magnitude of the auxiliary torque Ta1(θ) based on the steering angle |θ|. Furthermore, the ECU 100 (auxiliary unit 102) reduces the driving torque of the left motor 21, which drives the left steering wheel 11, by the amount of auxiliary torque Ta1(θ), and increases the driving torque of the right motor 22, which drives the right steering wheel 12, by the amount of auxiliary torque Ta1(θ).

[0100] For example, when the steering wheel 60 is rotated from a rotation angle of 0 degrees to -280 degrees, such as Figure 8As shown, until the rotation angle reaches -5 degrees, the driving torque TL of the left motor 21 is reduced by Tc2 relative to the torque TS, independent of the steering angle |θ|. After reaching -5 degrees, the driving torque TL of the left motor 21 gradually decreases with the increase of the steering angle |θ|. Moreover, after the rotation angle reaches 270 degrees, the driving torque TL is reduced by Tc1 relative to the torque TS, independent of the steering angle |θ|.

[0101] On the other hand, until the rotation angle reaches -5 degrees, the driving torque TR of the right motor 22 increases by an amount Tc2 relative to the torque TS, independent of the steering angle |θ|. After reaching -5 degrees, the driving torque TR of the right motor 22 gradually increases with the increase of the steering angle |θ|. Moreover, after the rotation angle reaches 270 degrees, the driving torque TR increases by an amount Tc1 relative to the torque TS, independent of the steering angle |θ|.

[0102] With this initial assistance, vehicle 1 smoothly transitions from a straight-ahead state (state 1) to a left-turning state (state 2) (see reference). Figure 6 ).

[0103] [Second Support]

[0104] When the steering wheel is turned 60 degrees from the negative direction ( Figure 6 In state 2), when the rotation starts to return to 0 degrees, the ECU100 (auxiliary unit 102) determines the auxiliary torque Ta1(θ) and starts the second auxiliary based on the auxiliary torque Ta1(θ).

[0105] The ECU 100 (auxiliary unit 102) determines the magnitude of the auxiliary torque Ta1(θ) based on the steering angle |θ|, just like the first auxiliary unit. Furthermore, the ECU 100 (auxiliary unit 102) increases the driving torque of the left motor 21, which drives the left steering wheel 11, by the amount of auxiliary torque Ta1(θ), and decreases the driving torque of the right motor 22, which drives the right steering wheel 12, by the amount of auxiliary torque Ta1(θ).

[0106] For example, when the steering wheel 60 is rotated from a rotation angle of -280 degrees to 0 degrees, such as Figure 9 As shown, until the rotation angle becomes less than -270 degrees, the driving torque TL of the left motor 21 increases by an amount Tc1 relative to the torque TS, independent of the steering angle |θ|. After the angle becomes less than -270 degrees, the decrease in the driving torque TL of the left motor 21 relative to the steering angle |θ| gradually decreases accordingly. Moreover, after the rotation angle becomes less than -5 degrees, the driving torque TL increases by an amount Tc2 relative to the torque TS, independent of the steering angle |θ|.

[0107] On the other hand, until the rotation angle becomes less than -270 degrees, the driving torque TR of the right motor 22 decreases by an amount Tc1 relative to the torque TS, independent of the steering angle |θ|. After the angle becomes less than -270 degrees, the decrease in the driving torque TR of the right motor 22 relative to the steering angle |θ| gradually increases accordingly. Moreover, after the rotation angle becomes less than -5 degrees, the driving torque TR decreases by an amount Tc2 relative to the torque TS, independent of the steering angle |θ|.

[0108] With this second assistance, vehicle 1 smoothly transitions from a left-turning state (state 2) to a straight-going state (state 3).

[0109] It should be noted that when vehicle 1 turns right, the driving torques TL and TR of the left and right motors 21 and 22 are adjusted according to... Figure 8 and Figure 9 The curve changes as the rotation angle is positive in the region.

[0110] In addition, when the first and second assists are terminated, the ECU100 (assistance unit 102) returns the driving torque of the motors 21 and 22 to TS.

[0111] As described above, the steering assist device of this embodiment, while the steering angle is increasing, sets the assist torque to a small value within a range where the steering angle is less than a second threshold. This reduces the amount of assist torque by decreasing the driving torque of the motor driving the steering wheel on the inside of the turn of vehicle 1, and increases the amount of assist torque by increasing the driving torque of the motor driving the steering wheel on the outside of the turn of vehicle 1. Thus, within a small steering angle range, by reducing the assist amount, a state where steering is not easily performed is maintained. This improves the straight-line stability of vehicle 1, making the driver feel that vehicle 1 is about to move straight.

[0112] On the other hand, within the range where the steering angle is above the second threshold, the larger the steering angle, the greater the increase in assist torque from the steering assist device. Thus, within the range of large steering angles, the larger the steering angle, the greater the assist amount, thereby reducing the force required for steering operation when the driver makes a left or right turn. That is, the driver can perform steering operations with less force.

[0113] Therefore, it is possible to reduce the force required for steering control while maintaining the straight-line stability of vehicle 1.

[0114] Furthermore, during the period when the steering angle is decreasing, the steering assist device increases the amount of auxiliary torque in the motor driving the steering wheel on the inside of the turn of vehicle 1, and decreases the amount of auxiliary torque in the motor driving the steering wheel on the outside of the turn of vehicle 1. This makes it easier to move from the tilted state of the steering wheels 11 and 12 towards the direction of straight-line travel, thus improving the straight-line stability of vehicle 1. Additionally, the steering wheel 60 rotates naturally with a rotation angle close to 0 degrees, further enhancing the driver's sense that vehicle 1 is about to move straight.

[0115] When the steering angle is above a first threshold, the auxiliary torque is a constant value independent of the steering angle. Therefore, the upper limit is set to the difference between the driving torques TL and TR of the left and right motors 21 and 22. Thus, it is possible to safely assist the steering control of vehicle 1.

[0116] It should be noted that vehicle 1 may also be a vehicle in which both the left and right front wheels and the left and right rear wheels are steering wheels, and it has multiple motors that independently drive these steering wheels. In this case, when the first assistance is executed, ECU 100 (assistance unit 102) reduces the driving torque of each motor driving the front and rear wheels on the inside of the turn by the amount of auxiliary torque Ta1(θ), and increases the driving torque of each motor driving the front and rear wheels on the outside of the turn by the amount of auxiliary torque Ta1(θ). Furthermore, when the second assistance is executed, ECU 100 (assistance unit 102) increases the driving torque of each motor driving the front and rear wheels on the inside of the turn by the amount of auxiliary torque Ta1(θ), and decreases the driving torque of each motor driving the front and rear wheels on the outside of the turn by the amount of auxiliary torque Ta1(θ).

[0117] (Modified Example)

[0118] The following section will describe the differences between the modified examples and the embodiments described above.

[0119] In the modified example, the ECU 100 (assistance unit 102) performs the first assistance by considering not only the steering angle |θ|, but also the angular velocity of the steering wheel 60. Specifically, the ECU 100 (assistance unit 102) increases or decreases the driving torque of the left and right motors 21 and 22 based on the assistance torque Ta2(θ, ω).

[0120] The auxiliary torque Ta2(θ, ω) is represented by the product of the auxiliary torque Ta1(θ) in the above embodiment and the coefficient k(ω), k(ω)Ta1(θ). k(ω) is determined by the angular velocity ω of the steering wheel 60 (that is, the time derivative of the rotation angle).

[0121] Figure 10This is a diagram showing the coefficient k(ω) of the auxiliary torque Ta2(θ, ω) of the modified ECU100 (auxiliary unit 102).

[0122] The coefficient k(ω) increases as the absolute value of the angular velocity |ω| increases. When the absolute value of the angular velocity |ω| is above the third threshold |ωt|, the coefficient k(ω) reaches its maximum value k1 (e.g., k1 = 1.2) regardless of the absolute value of the angular velocity |ω|. Furthermore, the coefficient k(ω) reaches its minimum value k2 (e.g., 1) when the absolute value of the angular velocity |ω| is 0.

[0123] In this modified example, a predetermined value Tc2, a coefficient k(ω), a maximum value k1, and a minimum value k2 are set so that the value of the auxiliary torque Ta2(θ, ω) when the steering angle |θ| is less than the second threshold is less than the minimum value of the auxiliary torque Ta2(θ, ω) when the steering angle |θ| is above the second threshold.

[0124] It should be noted that, similarly to the embodiment described above, the ECU100 (auxiliary unit 102) performs the second assistance based on the auxiliary torque Ta1(θ) which does not reflect the angular velocity ω.

[0125] According to this modified example, while the rotation angle is increasing, the auxiliary torque is also changed by taking into account the angular velocity of the steering wheel 60. Therefore, it is possible to assist the steering operation of the vehicle 1 while appropriately reflecting the driver's steering operation when turning left or right.

[0126] It should be noted that during the period when the rotation angle is decreasing, the ECU100 (auxiliary unit 102) can also perform a second assistance based on the auxiliary torque Ta2(θ, ω).

[0127] (Other variations)

[0128] When the steering angle is less than the second threshold, the auxiliary torque Ta1(θ) does not necessarily have to be a constant value, as long as it is at least below the minimum value of the auxiliary torque Ta1(θ) when the steering angle is above the first threshold. Therefore, when the steering angle is less than the second threshold, the auxiliary torque Ta1(θ) can also vary within a range below this minimum value.

[0129] When assisting the steering of vehicle 1 based on the auxiliary torque Ta2(θ, ω), if the steering wheel is rotated at a large angular velocity until the steering angle rises above the first threshold, the auxiliary torque Ta2(θ, ω) may become very large. Therefore, an upper limit can be set for the auxiliary torque Ta2(θ, ω). This allows for safer assistance with the steering of vehicle 1.

[0130] The aforementioned steering control device 70 can also be a ball nut type steering control device or a steering control device based on a drive-by-wire system.

[0131] In the above embodiments and modifications, vehicle 1 was described as a hub-and-spoke locomotive with a kingpin angle of 0 degrees and a caster angle of 0 degrees when unloaded. However, the steering assist device of this disclosure can be applied to any vehicle that has at least a plurality of motors that independently drive the left and right steering wheels. That is, the steering assist device of this disclosure can also be applied to vehicles other than hub-and-spoke locomotives.

[0132] Furthermore, the steering assist device disclosed herein is more suitable for vehicles where the kingpin offset R is not 0 and the absolute value of the caster angle is less than 2 degrees.

[0133] The above embodiments and modifications are merely examples of specific implementations of this disclosure, and the technical scope of this disclosure should not be limited by these embodiments and modifications. That is, this disclosure can be implemented in various forms without departing from the essential points or main features of this disclosure.

[0134] This application is based on Japanese patent application (Japan Patent Application No. 2021-180249) filed on November 4, 2021, the contents of which are incorporated herein by reference.

[0135] Industrial applicability

[0136] The steering assist device, steering assist method, and vehicle disclosed herein can reduce the force required for steering while maintaining the straight-line stability of the vehicle, and therefore have great industrial applicability.

[0137] Explanation of reference numerals in the attached figures

[0138] 1 vehicle

[0139] 11, 12, 212 Steering control wheels

[0140] Motors 21 and 22

[0141] Inverters 23 and 24

[0142] 31, 32, 232 steering knuckles

[0143] 41, 42 Steering tie rods

[0144] 60 Steering Wheel

[0145] 61 Steering Axle

[0146] 62. Pinion Components

[0147] 63 rack and pinion shaft

[0148] 70 Steering control device

[0149] 80 Steering Angle Sensor

[0150] 100ECU (Steering Assist Device)

[0151] 101 Testing Department

[0152] 102 Auxiliary Department

Claims

1. A steering assist device for assisting steering of a vehicle with a kingpin offset, characterized in that it comprises: The testing department tests the steering wheel angle; and The auxiliary unit adjusts the driving torque based on the auxiliary torque. When the steering angle is above a threshold, the larger the steering angle, the greater the auxiliary torque. When the steering angle is below the threshold, the auxiliary torque is a value below the minimum value of the auxiliary torque when the steering angle is above the threshold. During the period when the steering angle is increasing, the auxiliary unit reduces the driving torque of the first motor by the amount of the auxiliary torque and increases the driving torque of the second motor by the amount of the auxiliary torque. The first motor is a motor that drives the steering wheel on the inside of the vehicle's turn, and the second motor is a motor that drives the steering wheel on the outside of the vehicle's turn.

2. The steering assistance device as claimed in claim 1, wherein, During the period when the steering angle is decreasing, the auxiliary unit increases the driving torque of the first motor by the amount of the auxiliary torque and decreases the driving torque of the second motor by the amount of the auxiliary torque.

3. The steering assistance device as described in claim 1, wherein, The detection unit detects the angular velocity of the steering wheel. The greater the angular velocity, the greater the auxiliary torque produced by the auxiliary unit.

4. A steering control assistance method for assisting the steering control of a vehicle with a kingpin offset, characterized by comprising the following steps: Detect the steering wheel angle; as well as During the period when the steering angle is increasing, based on the auxiliary torque, the driving torque of the first motor is reduced by the amount of the auxiliary torque, and the driving torque of the second motor is increased by the amount of the auxiliary torque. When the steering angle is above a threshold, the larger the steering angle, the larger the auxiliary torque. When the steering angle is below the threshold, the auxiliary torque is a value below the minimum value of the auxiliary torque when the steering angle is above the threshold. The first motor is a motor that drives the steering wheel on the inside of the vehicle's turn, and the second motor is a motor that drives the steering wheel on the outside of the vehicle's turn.

5. A vehicle, characterized in that, It has the steering assist device as described in claim 1.

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