Steering system for vehicles

Abstract

The steering system is equipped with a control unit (15) configured to determine a target steering angle (αt) based on the steering angle (β) of the steering shaft (18) engaged with the steering wheel (19) and drive the steering actuator to make the steering angle (α) match the target steering angle, and to determine a target reaction force (Tt) based on the steering state of the wheel and drive the reaction force actuator (13) to make the reaction force match the target reaction force. The control unit is configured to correct the output of the steering angle sensor in such a way that the geometric steering center of the steering wheel matches the mechanical steering center of the steering shaft when a specified input (S) is received from the manual input switch (37).

Description

Technical Field

[0001] This invention relates to a steer-by-wire system for vehicles. Background Technology

[0002] A known steer-by-wire system for a vehicle includes: a steering input mechanism, such as a steering wheel configured for operation by a vehicle operator; and a steering mechanism mechanically separated from the steering input mechanism and configured to change the steering angle of the wheels. The steering mechanism is driven by a steering actuator that generates a driving force to change the steering angle of the wheels. A reaction force actuator applies a reaction force to the steering input mechanism in response to the steering operation.

[0003] Regarding such steer-by-wire systems, prior art improves operational efficiency when assembling a switch assembly including a steering angle sensor and a steering wheel to a steering shaft assembly (Patent Document 1). According to this prior art, the steering shaft assembly is provided with a shaft positioning mechanism that rapidly positions and secures the steering shaft to the housing via rotation. Furthermore, the switch assembly is provided with a collar positioning mechanism for rapidly positioning and securing the actuator collar to the housing via rotation.

[0004] List of cited references

[0005] Patent documents

[0006] [Patent Document 1] JP2010-264942A Summary of the Invention

[0007] Technical issues

[0008] However, in the prior art disclosed in Patent Document 1, the structure of the operating device becomes complex and the system is large and costly because it requires a shaft positioning mechanism and a collar positioning mechanism.

[0009] In view of this problem with the prior art, the main objective of the present invention is to improve work efficiency when assembling steering systems without increasing system size or cost.

[0010] Solution to the problem

[0011] To achieve this objective, the present invention provides a steering system (1) for a vehicle (2), the steering system comprising: a steering wheel (19) configured for operation by a driver; a steering shaft (18) connected to the steering wheel in a rotational motion transmission manner; a steering mechanism (11) mechanically separated from the steering shaft and configured to steer the wheels (3) of the vehicle; a steering angle sensor (21) detecting a steering angle (β) about a control steering center (β=0) as the angular position of the steering shaft corresponding to the straight-ahead state of the vehicle; a steering actuator (12) providing a driving force to the steering mechanism; and a steering angle sensor (32) for use with the steering angle sensor (32). The steering angle sensor detects the steering angle (α) of the wheel; a reaction force actuator (13) applies a reaction force (T) to the steering wheel in response to a steering operation; and a control unit (15) configured to determine a target steering angle (αt) based on the steering angle (β) and drive the steering actuator to make the steering angle (α) match the target steering angle, and to determine a target reaction force (Tt) based on the steering state of the wheel and drive the reaction force actuator to make the reaction force match the target reaction force, wherein the control unit is configured to correct the output of the steering angle sensor when a specified input is received, such that the current steering angle corresponds to the control steering center.

[0012] According to this arrangement, even when the steering wheel is assembled to the steering shaft and the geometric center of the steering wheel deviates angularly from the control steering center of the steering shaft, the output of the steering angle sensor can be corrected by forwarding a predetermined input from the manual input switch to the control unit when the steering wheel is at the geometric steering center, so that the steering angle (geometric steering center) at the time of assembly corresponds to the control steering center. In other words, even if an angular error occurs during steering wheel assembly, the current steering angle (determined by the angular position of the steering shaft) can be reset to the control steering center without reassembling the steering wheel. Therefore, the efficiency of assembling the steering system is improved. Furthermore, since the steering system does not require a physical positioning mechanism, increases in the size and cost of the steering system can be avoided.

[0013] Preferably, the control unit is configured to: correct the output of the steering angle sensor when a predetermined time period has elapsed since the moment the specified input was received, and temporarily stop driving the reaction force actuator before the predetermined time period has elapsed since the moment the specified input was received.

[0014] Alternatively, the control unit may be configured to: correct the output of the steering angle sensor when a predetermined time period has elapsed since the moment the specified input was received, and temporarily reduce the target reaction force before the predetermined time period has elapsed since the moment the specified input was received.

[0015] Alternatively, the control unit may be configured to: correct the output of the steering angle sensor when a predetermined time period has elapsed since the moment the specified input was received, and set a dead zone in the deviation before the predetermined time period has elapsed since the moment the specified input was received.

[0016] According to these arrangements, during the calibration of the steering center, the steering wheel is prevented from being turned by a reaction force actuator, which, under the control of the control unit, can turn the steering wheel according to the steering state of the wheels. Thus, the operator can properly correct the output of the steering angle sensor without being hindered by the reaction force, ensuring that the geometric steering center of the steering wheel is aligned with the control steering center of the steering shaft.

[0017] Preferably, the steering system for the vehicle further includes a physical stop (43) that defines a physical maximum steering angle (βmP) of the steering shaft in each rotational direction from the control steering center, and the control unit is configured to define a controlled maximum steering angle (βmC) of the steering wheel in each rotational direction from the control steering center, the controlled maximum steering angle being less than the physical maximum steering angle, and the control unit is configured to drive the reaction force actuator to generate a steering limiting reaction force (Tsl) defining the controlled maximum steering angle.

[0018] According to this arrangement, the rotation of the steering shaft is regulated by a physical stop, thereby avoiding problems such as damage to the wiring harness due to excessive rotation of the steering shaft. Furthermore, the control unit generates a steering limiting reaction force to prevent the steering shaft from colliding with the physical stop. As a result, collision noise and impacts due to collisions are avoided. Because the maximum control angle of the steering wheel is uniformly set in each rotational direction starting from the control steering center, the maximum steering angle can remain uniform in both rotational directions.

[0019] In the arrangement where the control unit sets the maximum steering angle, preferably, when the specified input is received with the steering wheel set to its geometric steering center, and it is determined that the maximum steering angle will exceed the physical maximum steering angle, the control unit prohibits the correction of the steering angle sensor output.

[0020] When the maximum steering angle exceeds the physical maximum steering angle, the maximum steering angle in one direction of rotation becomes smaller than the maximum steering angle in the other direction of rotation, causing the maximum steering angle to become uneven between the two directions of rotation. In this case, the control unit disables the correction of the steering angle sensor output, thereby preventing the maximum steering angle from becoming uneven between the two directions of rotation.

[0021] In the arrangement where the control unit sets the maximum steering angle, preferably, when the specified input is received with the steering wheel set to its geometric steering center and it is determined that the maximum steering angle will exceed the physical maximum steering angle, the control unit corrects the output of the steering angle sensor so that the current steering angle is as close as possible to the steering center, without causing the maximum steering angle to exceed the physical maximum steering angle.

[0022] According to this arrangement, the geometric steering center of the steering wheel can be made as close as possible to the control steering center of the steering wheel, without making the maximum control steering angle exceed the physical maximum steering angle.

[0023] In the arrangement where the control unit sets the maximum steering angle, preferably, when the specified input is received when the steering wheel is set to the geometric steering center, and it is determined that the maximum steering angle will exceed the physical maximum steering angle, the control unit corrects the output of the steering angle sensor so that the geometric steering center of the steering wheel is aligned with the control steering center of the steering shaft, and changes the ratio (K) of the steering angle to the steering angle to a smaller value so that the maximum steering angle does not exceed the physical maximum steering angle.

[0024] Therefore, the output of the steering angle sensor is calibrated so that the geometric steering center of the steering wheel is aligned with the mechanical steering sensor of the steering shaft. By changing the ratio of the steering angle to the steering angle in a way that controls the maximum steering angle from exceeding the physical maximum steering angle, the maximum usable steering angle of the wheel can be ensured, and the physical maximum steering angle can be prevented from becoming uneven in the two directions of rotation.

[0025] Preferably, the steering system for the vehicle further includes a control steering center setting switch (37) disposed in the vehicle for generating the specified input.

[0026] According to this arrangement, workers or operators can easily correct the output of the steering angle sensor by operating the steering center setting switch.

[0027] Alternatively, the specified input may be an input from a vehicle diagnostic device (39) that is detachably connected to the vehicle.

[0028] This arrangement prevents users or drivers from accidentally calibrating the output of the steering angle sensor while the vehicle is in motion.

[0029] Beneficial effects of the invention

[0030] Therefore, the present invention improves work efficiency when assembling steering systems without increasing system size or cost. Attached Figure Description

[0031] [ Figure 1 ] Figure 1 This is a schematic diagram of a steering system according to an embodiment of the present invention.

[0032] [ Figure 2 ] Figure 2 This is a simplified cross-sectional view of the steering input mechanism.

[0033] [ Figure 3 ] Figure 3 This is a schematic diagram illustrating an example of the relationship between the physical maximum steering angle and the controlled maximum steering angle when the steering input mechanism is correctly assembled.

[0034] [ Figure 4 ] Figure 4 This is a schematic diagram illustrating an example of output correction for a steering angle sensor under conditions of small assembly errors.

[0035] [ Figure 5 ] Figure 5 This is a schematic diagram illustrating a first example of output correction for a steering angle sensor under conditions of large assembly errors.

[0036] [ Figure 6 ] Figure 6 This is a schematic diagram illustrating a second example of output correction for a steering angle sensor under conditions of large assembly errors.

[0037] [ Figure 7 ] Figure 7 This is a schematic diagram illustrating a third example of output correction for a steering angle sensor under conditions of large assembly errors. Detailed Implementation

[0038] The following describes a steering system 1 for a vehicle 2 according to an embodiment of the present invention. Figure 1 As shown, the steering system 1 includes a steer-by-wire (SBW) system. The vehicle 2 equipped with the steering system 1 is a four-wheeled vehicle with left and right front wheels 3 and left and right rear wheels (not shown in the figure). The left and right front wheels 3 are controlled by the vehicle body 8 via their respective steering knuckles 7. Figure 1(Only the lower outline of the front wheel is shown in the diagram) The steering system 1 provides support so that the steering angle α of the front wheel 3 can be changed, and the front wheel 3 thus functions as a steerable wheel. The steering angle α refers to the angle of the front wheel 3 relative to the fore-and-aft direction in the top view. Therefore, the steering system 1 changes the steering angle α of the front wheel 3.

[0039] The steering system 1 includes a steering input mechanism 10 rotatably mounted on the vehicle body 8, a steering mechanism 11 for steering the front wheels 3, a steering actuator 12 for applying driving force to the steering mechanism 11, a reaction force actuator 13 for applying a reaction torque T to the steering input mechanism 10, and a control unit 15 for controlling the reaction force actuator 13 and the steering actuator 12. The steering system 1 may be a redundant system comprising multiple sets, each set independently equipped with a steering actuator 12, a reaction force actuator 13, and a control unit 15.

[0040] The steering input mechanism 10 accepts steering inputs from the vehicle operator. The steering input mechanism 10 includes a steering shaft 18 rotatably supported by the vehicle body 8 and a steering wheel 19 disposed at the end of the steering shaft 18. The steering shaft 18 is rotatably supported by a steering column 20 disposed on the vehicle body 8, and the rear end of the steering shaft 18 protrudes rearward from the steering column 20. The steering wheel 19 is connected to the rear end of the steering shaft 18 so as to rotate integrally with the steering shaft 18. Therefore, the steering shaft 18 is connected to the steering wheel 19 so as to transmit rotational motion of the steering wheel 19 to the steering shaft 18.

[0041] The reaction force actuator 13 includes an electric motor connected to the steering shaft 18 via a gear mechanism. When the reaction force actuator 13 is driven, the driving force is transmitted to the steering shaft 18 as a rotational force. The reaction force actuator 13 applies a rotational torque to the steering input mechanism 10. The torque applied to the steering input mechanism 10 by the reaction force actuator 13 in response to steering operation is called the reaction torque T.

[0042] The steering system 1 is also provided with a steering angle sensor 21, which detects the rotation angle of the steering shaft 18 about its central axis as the steering angle β. The steering angle is given as the rotation angle of the steering shaft 18 relative to a predetermined control steering center (which coincides with the mechanical steering center of the steering mechanism, except in special cases discussed below). The steering angle sensor 21 may be a rotary encoder, which is known per se. In addition, the steering system 1 is provided with a torque sensor 22, which detects the torque applied to the steering shaft 18 as the steering torque Ts. The torque sensor 22 detects the steering torque Ts applied to the portion of the steering shaft 18 located between the steering wheel 19 and the reaction force actuator 13. The steering torque Ts is determined by the operating torque applied by the vehicle operator to the steering wheel 19 and the reaction torque T applied by the reaction force actuator 13 to the steering shaft 18. The torque sensor 22 may include a torque sensor known per se, such as a magnetostrictive torque sensor or a strain gauge, or alternatively, the steering torque may be estimated based on the current value flowing through the electric motor of the reaction force actuator 13.

[0043] The steering system 1 also includes a first rotation angle sensor 23 for detecting the rotation angle θ of the reaction force actuator 13. The first rotation angle sensor 23 may be a known solver or rotary encoder.

[0044] The steering mechanism 11 has a rack 26 extending in the lateral direction of the vehicle. The rack 26 is supported by a gearbox 27 so that it can move in the lateral direction of the vehicle. The left and right ends of the rack 26 are connected to steering knuckles 7, which support the left and right front wheels 3 via corresponding tie rods 30. When the rack 26 moves in the lateral direction of the vehicle, the steering angle α of the front wheels 3 is changed. The steering mechanism 11 is mechanically separated from the steering input mechanism 10.

[0045] The steering actuator 12 includes an electric motor. Based on a signal from the control unit 15, the steering actuator 12 moves the rack 26 in the lateral direction of the vehicle, and accordingly changes the steering angle α of the left and right front wheels 3. The steering actuator 12 is incorporating a variable ratio mechanism that allows the ratio K of the steering angle β to the steering angle α to change (K = β / α). Therefore, the steering angle α of the front wheels 3 can be changed while the steering angle β remains constant.

[0046] The steering system 1 is also provided with a second rotation angle sensor 31 for detecting the rotation angle θ of the steering actuator 12. The second rotation angle sensor 31 may be a known solver or rotary encoder. In addition, the steering system 1 has a driven angle sensor 32 for detecting the driven angle α of the front wheels 3. In this embodiment, the driven angle sensor 32 includes a rack travel sensor for detecting the rack position (the position of the rack 26 in the lateral direction of the vehicle), and the driven angle α of the front wheels 3 is determined by the rack position.

[0047] The control unit 15 comprises an electronic control unit including a CPU, a memory, and a storage device for storing programs. A steering angle sensor 21, a torque sensor 22, a first rotation angle sensor 23, a second rotation angle sensor 31, and a steering angle sensor 32 are connected to the control unit 15. Based on signals from these sensors, the control unit 15 acquires signals corresponding to the steering angle β, steering torque Ts, rotation angle θ of the reaction force actuator 13, rotation angle θ of the steering actuator 12, and steering angle α. Furthermore, the control unit 15 is connected to a vehicle speed sensor 33, a yaw rate sensor 34, and a lateral acceleration sensor 35, and acquires signals corresponding to the vehicle speed V, yaw rate γ, and lateral acceleration Gy.

[0048] Control unit 15 is connected to reaction force actuator 13 and steering actuator 12 to control reaction force actuator 13 and steering actuator 12. Control unit 15 controls steering actuator 12 according to steering angle β and controls reaction force actuator 13 according to steering angle α.

[0049] The control operation mode of control unit 15 in SBW mode is discussed below. Control unit 15 calculates the target driven angle αt based on the steering angle β detected by steering angle sensor 21. Control unit 15 can calculate the target driven angle αt (αt = β / K) by, for example, dividing the steering angle β by the gear ratio K. The gear ratio K is preferably 2 to 30, and more preferably 8. Control unit 15 calculates the first current value A1 to be supplied to steering actuator 12 based on the deviation Δα (= αt - α) between the target driven angle αt and the actual driven angle α, such that the driven angle α matches the target driven angle αt. Therefore, control unit 15 performs feedback control of steering actuator 12 based on the deviation Δα. As the deviation Δα increases, the first current value A1 supplied to steering actuator 12 increases, the output of steering actuator 12 increases, and the change in driven angle α increases.

[0050] The control unit 15 calculates the target reaction torque Tt to be generated in the reaction force actuator 13 based on the steering state of the front wheel 3, and in particular on the deviation Δα. The target reaction torque Tt can be calculated by multiplying Δα by a predetermined coefficient. Then, the control unit 15 calculates the second current value A2 to be supplied to the reaction force actuator 13 based on the calculated target reaction torque Tt. The second current value A2 to be supplied to the reaction force actuator 13 can be determined relative to the target reaction torque Tt with reference to a predetermined mapping. Alternatively, the control unit 15 can determine the second current value A2 based on the deviation Δα with reference to a predetermined mapping. The values ​​of the target reaction torque Tt and the second current value A2 increase as the deviation Δα of the steering angle α increases.

[0051] Control unit 15 supplies a second current value A2 to reaction force actuator 13, generating a corresponding driving force in reaction force actuator 13. The driving force generated by reaction force actuator 13 is applied to steering shaft 18 as a reaction torque T, which is opposite to the vehicle operator's input. As a result, the vehicle operator can receive a reaction force (resistance) applied to steering wheel 19 to resist steering operation.

[0052] Vehicle 2 is equipped with a steering center setting switch 37, which serves as a manual input switch for transmitting a steering center setting signal S to control unit 15. The steering center setting switch 37 is configured to accept manual input and generate a steering center setting signal S when a manual input is received. Figure 1 As shown by the dashed line, alternatively, the steering center setting switch 37 can be located in the vehicle diagnostic device 39, which is separate from the vehicle 2, and can be selectively connected to the control unit 15.

[0053] Figure 2 This is a schematic cross-sectional view of the steering input mechanism 10. As described above, the steering shaft 18 is rotatably supported by the steering column 20. Figure 2 As shown, a protrusion 41 is formed on the outer surface of the steering shaft 18, and a receiving groove 42 for receiving the protrusion 41 is formed on the steering column 20. The receiving groove 42 is formed on the inner periphery of the steering column 20 within an angular range of less than 360 degrees, and the end wall defining the corresponding end of the receiving groove 42 forms a physical stop 43 that restricts the movement of the protrusion 41.

[0054] When the steering wheel 19 is turned clockwise, the protrusion 41 eventually contacts the right-side physical stop 43. The angular position of the protrusion 41 against the right-side physical stop 43 is the right-side physical end PE of the steering shaft 18. When the steering wheel 19 is turned counterclockwise, the protrusion 41 eventually contacts the left-side physical stop 43. The angular position of the protrusion 41 against the left-side physical stop 43 is the left-side physical end PE of the steering shaft 18. The center between the right-side and left-side physical ends PE is the mechanical steering center of the steering shaft 18. The angular range from the mechanical steering center of the steering shaft 18 to the right-side physical end PE is the right-side maximum physical steering angle βmP, and the angular range from the mechanical steering center of the steering shaft 18 to the left-side physical end PE is the left-side maximum physical steering angle βmP. Therefore, the left and right physical stops 43 each define the left and right maximum physical steering angles βmP of the steering shaft 18.

[0055] The geometric center of the steering wheel 19, or the neutral position of the steering input mechanism 10 as perceived by the driver, is typically aligned with the mechanical steering center of the steering shaft 18. When the steering shaft 18 turns toward its physical end PE, impact noise is generated, and this impact can potentially damage the mechanical durability of the steering input mechanism 10. Therefore, it is desirable to avoid this noise and damage to durability.

[0056] Similar physical constraints are also imposed on the front wheels 3, and particularly in the steering mechanism 11. The front wheels 3 can be steered only up to their physical ends PE in each direction. The physical ends PE can be defined in various ways, but are typically defined by the end of the travel of the rack 26, commonly referred to as the "rack end". The center between the left and right travel ends of the rack 26 is the mechanical steering center of the steering mechanism 11, which generally coincides with the position of the front wheels 3 when the vehicle is traveling straight, or when the steering angle α of the steering mechanism 11 is 0°. The ratio K (=β / α) of the steering angle β to the steering angle α is set such that the physical end PE of the steering shaft 18 corresponds to the physical end PE of the rack 26. When the front wheels 3 are steered to the rack end, impact noise is generated, and the mechanical durability of the steering mechanism 11 may be compromised due to the impact. It is desirable to avoid this noise and durability impairment.

[0057] In this embodiment, the control end CE, which limits the rotation of the steering shaft 18, is set at an angle β0 smaller than the physical end PE for each rotation direction. The control steering center (angle position where steering angle β = 0) of the steering input mechanism 10 corresponds to the rotation angle of the steering shaft that makes the steering angle α of the front wheels 3 approximately zero, and the vehicle 2 is traveling straight. Ideally, the control steering center should correspond to the geometric steering center of the steering wheel 19. The angular range from the control steering center of the steering shaft 18 to the right control end CE is defined as the right maximum control steering angle βmC, and the angular range from the control steering center of the steering shaft 18 to the left control end CE is defined as the left maximum control steering angle βmC. The target steering angle αt is related to the steering angle β in a manner that the steering angle α of the front wheels 3 increases with the increase of the steering angle β. However, when the steering angle β increases beyond the control end CE, the command to the steering actuator 12 is limited to the maximum control steering angle corresponding to the maximum control steering angle βmC. In other words, when the steering input mechanism 10 rotates beyond the maximum control steering angle βmC, the front wheels 3 are only steered until the maximum control steering angle is reached. The maximum control steering angle is less than the physical maximum steering angle.

[0058] The reaction torque T applied to the steering input mechanism 10 is typically controlled to increase independently of the deviation Δα between the steering angle α and the target steering angle αt. However, when the steering angle β is equal to or greater than the controlled maximum steering angle βmC, the control unit 15 applies a steering limiting reaction torque Ts1 to the steering input mechanism 10 to prevent the steering input mechanism 10 from rotating beyond the controlled maximum steering angle βmC. The steering limiting reaction torque Ts1 is a value that is substantially greater than the normal value of the reaction torque T that might occur under other conditions. The control unit 15 calculates a second current value A2 that needs to be supplied to the reaction force actuator 13 to generate the steering limiting reaction torque Ts1.

[0059] When the steering angle β of the front wheel 3 reaches the maximum control steering angle βmC, the steering limiting reaction torque Ts1 is applied to the steering input mechanism 10. As a result, the driver recognizes that the steering angle α of the front wheel 3 has reached its maximum angle due to the reaction force received from the steering input mechanism 10, and is thus prompted not to over-rotate the steering input mechanism 10.

[0060] As described above, the steering system 1 is equipped with physical stoppers 43 on the left and right sides of the steering shaft 18, which limit the physical maximum steering angle βmP. Therefore, problems such as damage to the wiring harness due to excessive rotation of the steering shaft 18 can be avoided.

[0061] Furthermore, the control unit 15 sets a control maximum steering angle βmC that is smaller than the physical maximum steering angle βmP, and drives the reaction force actuator 13 to generate a steering limiting reaction torque Ts1 that limits the control maximum steering angle βmC. When the control unit 15 generates the steering limiting reaction torque Ts1, it prevents the steering shaft 18 from colliding with the physical stop 43. As a result, even when the steering wheel 19 is over-rotated, collision noise and impact are generated. Since the control maximum steering angle βmC of the steering wheel 19 is set on each side of the geometric steering center of the steering wheel 19 (clockwise and counterclockwise rotation), the maximum steering angle of the steering wheel 19 is evenly distributed to the left and right.

[0062] Figure 3 This is a graph showing the relationship between the physical maximum steering angle βmP and the control maximum steering angle βmC as a result of proper assembly. (See figure.) Figure 3 As shown, the steering wheel 19 is properly fitted to the steering shaft 18 such that the geometric steering center of the steering wheel 19 coincides with the mechanical steering center of the steering shaft 18 (which in this case is the same as the control steering center). The steering angle β of the steering shaft 18 (angular displacement relative to the steering center β = 0) detected by the steering angle sensor 21 and the angular displacement of the steering wheel 19 relative to the geometric steering center perceived by the driver are consistent with each other.

[0063] However, when assembling vehicle 2 at the factory, steering wheel 19 may be assembled to steering shaft 18 in such a way that the geometric steering center of steering wheel 19 is offset from the mechanical steering center of steering shaft 18. It is also possible that when steering wheel 19 is removed from steering shaft 18 and reassembled during post-factory maintenance, the geometric steering center of steering wheel 19 may be offset from the mechanical steering center of steering shaft 18.

[0064] Figure 4 This diagram illustrates the process of correcting the output of the steering angle sensor 21 when a small assembly error occurs during the installation of the steering wheel 19. In this example, as... Figure 4 As shown in (A), the steering wheel 19 is assembled to the steering shaft 18 such that when the steering shaft 18 is at the mechanical steering center, the steering wheel 19 rotates slightly to the left from its geometric steering center. Alternatively, as... Figure 4 As shown in (B), the steering wheel 19 is assembled to the steering shaft 18 such that the steering wheel 19 is located at the geometric steering center, while the steering shaft 18 is rotated slightly to the right from its mechanical steering center.

[0065] In either case, the person performing the assembly work can easily correct the output of the steering angle sensor 21 by operating the steering center setting switch 37 and inputting the steering center setting signal S to the control unit 15. More specifically, as Figure 4 As shown in (B), with the steering wheel 19 at the geometric steering center, the operator manually operates the steering center setting switch 37. When the steering center setting switch 37 is operated, a steering center setting signal S is generated and forwarded to the control unit 15. Upon receiving the steering center setting signal S, the control unit 15 corrects the output of the steering angle sensor 21 so that the current steering angle β reaches or approaches the value corresponding to the steering center (β = 0).

[0066] As a result, the worker can correct the output of the steering angle sensor 21 so that the steering angle β corresponds to the value controlling the steering center. In other words, even if a setting error occurs during the assembly of the steering wheel 19, the output of the steering angle sensor 21 can be reset to the value corresponding to the mechanical steering center when the steering wheel 19 is held at its geometric steering center, without the need to reassemble the steering wheel 19. Therefore, the work efficiency during the assembly of the steering system 1 can be improved. Furthermore, since the steering system 1 does not require a physical positioning mechanism, the increase in the size and cost of the steering system 1 can be avoided.

[0067] The steering center setting switch 37 can be a switch installed on the vehicle 2 as described above. By installing the steering center setting switch 37 in the vehicle 2, the operator can easily correct the output of the steering angle sensor 21 by operating the steering center setting switch 37.

[0068] Alternatively, the steering center setting switch 37 can be a switch located in the vehicle diagnostic device 39, which is separate from the vehicle 2 as described above. In this case, when an operator operates the steering center setting switch 37 of the vehicle diagnostic device 39, the vehicle diagnostic device 39 generates a steering center setting signal S and forwards the steering center setting signal S from the vehicle diagnostic device 39 to the control unit 15. Since the steering center setting signal S is an input from the vehicle diagnostic device 39, which is selectively connected to the vehicle 2, it prevents the vehicle user or driver from incorrectly correcting the output of the steering angle sensor 21, for example, while the vehicle 2 is in motion.

[0069] When calibrating or adjusting the output of the steering angle sensor 21, the control unit 15 can adjust the output of the steering angle sensor 21 so that the current steering angle corresponds to the mechanical steering center after a predetermined time period has elapsed since the steering center setting signal S was received. Alternatively, the control unit 15 can temporarily stop driving the reaction force actuator 13 before a predetermined time period has elapsed since the steering center setting signal S was received.

[0070] As a result, during the calibration of the control steering center, under the control of the control unit 15, the steering wheel 19 is prevented from being rotated by the reaction force that may be generated by the reaction force actuator 13, based on the steering state of the front wheels 3. Therefore, the operator can correct the output of the steering angle sensor 21 so that when the steering wheel 19 is held at the geometric steering center, the current steering angle corresponds to the control steering center, without worrying about reaction forces that might interfere with the calibration process.

[0071] Alternatively, the control unit 15 may correct the output of the steering angle sensor 21 when a predetermined time has elapsed since the moment the specified input is received, and temporarily reduce the target reaction torque Tt from the moment the specified input is received until the predetermined time has elapsed.

[0072] Furthermore, from the moment the specified input is received until a predetermined time has elapsed, the control unit 15 can set a dead zone in the deviation Δα between the target steering angle αt and the steering angle α used to set the target reaction torque Tt.

[0073] In either case, during the calibration of the steering center, the steering wheel 19 is prevented from being turned by a reaction force actuator, which, under the control of the control unit 15, can turn the steering wheel according to the steering state of the wheels. Thus, the operator can properly correct the output of the steering angle sensor 21 without being hindered by the reaction force, ensuring that the geometric steering center of the steering wheel is aligned with the mechanical steering center of the steering shaft.

[0074] Figure 5This is an illustrative diagram showing a first example of output correction of the steering angle sensor 21 under conditions of large assembly errors. In this example, the steering wheel 19 is assembled to the steering shaft 18, with... Figure 4 Compared to case (B), its geometric steering center is significantly offset to the right at an angle from the mechanical steering center of steering shaft 18. In this case, if control unit 15 corrects the output of steering angle sensor 21 so that the current steering angle β corresponds to the value of the control steering center, the control maximum steering angle βmC exceeds the physical maximum steering angle βmP. In other words, the control end CE on the corresponding side is angularly ahead of the corresponding physical end PE. Therefore, in this case, control unit 15 prohibits correction of the output of steering angle sensor 21.

[0075] When the maximum steering angle βmC exceeds the physical maximum steering angle βmP, the maximum steering angle in one direction becomes smaller than the maximum steering angle in the other direction, and the maximum steering angle becomes uneven between the left and right sides (clockwise and counterclockwise). In this embodiment, the control unit 15 disables the calibration of the steering angle sensor 21 to prevent the maximum steering angle from becoming uneven between the left and right sides.

[0076] Figure 6 This is an illustrative diagram showing a second example of output correction for the steering angle sensor 21 under conditions of large assembly errors. Also in this example, as... Figure 6 As shown in (A), the steering wheel 19 is assembled to the steering shaft 18 such that the geometric steering center of the steering wheel is significantly offset to the right at an angle from the mechanical steering center of the steering shaft 18. Therefore, when the control unit 15 corrects the output of the steering angle sensor 21 so that the current steering angle β is the value corresponding to the control steering center, the control maximum steering angle βmC exceeds the physical maximum steering angle βmP.

[0077] Therefore, as Figure 6 As shown in (B), when a specified input is received with the current steering angle set to the geometric steering center, the control unit 15 corrects the output of the steering angle sensor 21 so that the current steering angle β is as close as possible to the mechanical steering center without causing the controlled maximum steering angle βmC to exceed the physical maximum steering angle βmP. More specifically, the control unit 15 corrects the output of the steering angle sensor 21 so that the angle of the right control end CE is equal to or less than the angle of the right physical end PE.

[0078] Thus, the geometric steering center of the steering wheel 19 can be made as close as possible to the control steering center without causing the maximum control steering angle βmC to exceed the physical maximum steering angle βmP.

[0079] Figure 7This is an illustrative diagram showing a third example of output correction for the steering angle sensor 21 under conditions of large assembly errors. Also in this example, as... Figure 7 As shown in (A), the steering wheel 19 is assembled to the steering shaft 18 such that the geometric steering center of the steering wheel is significantly offset to the right at an angle from the mechanical steering center of the steering shaft 18. Therefore, when the control unit 15 corrects the output of the steering angle sensor 21 so that the current steering angle β is the value corresponding to the control steering center, the control maximum steering angle βmC exceeds the physical maximum steering angle βmP.

[0080] Therefore, as Figure 7 As shown in (B), the control unit 15 sets the current steering angle β to a value corresponding to the mechanical steering center (β=0), and changes the ratio K of the steering angle β to the steering angle α to a smaller value, so that the maximum control steering angle βmC falls within the physical maximum steering angle βmP.

[0081] As a result, the output of the steering angle sensor 21 is corrected so that when the steering wheel is at the geometric steering center, the steering angle β of the steering shaft 18 is at the control steering center. Furthermore, the control unit 15 changes the ratio K so that the control maximum steering angle βmC is within the physical maximum steering angle βmP, thereby maintaining the maximum steering angle of the front wheels 3 and preventing the maximum steering angle from becoming uneven between the left and right sides.

[0082] The invention has been described according to specific embodiments, but the invention is not limited to these embodiments and can be modified in various ways without departing from the scope of the invention. For example, the physical stop 43 may be configured such that the steering shaft 18 can rotate within an angular range greater than 360 degrees. In this case, the physical stop 43 may be configured to selectively protrude into the receiving recess 42. Alternatively, the physical stop 43 may be removed, allowing the steering shaft 18 to rotate without restriction. In this case, since the physical end PE is absent, it is not necessary to limit the rotation as described above. Figures 5 to 7 The aforementioned correction. Furthermore, the control unit 15 can configure the steering angle sensor 21 such that the average value (which may be appropriately weighted) of the steering angle β over a predetermined time period starting from the moment the steering center setting signal S is input is set to a value corresponding to the mechanical steering center.

[0083] Furthermore, the specific configuration, arrangement, quantity, angle, procedure, etc., of each component and part can be appropriately changed without departing from the spirit of the invention. Moreover, all components shown in the above embodiments are not essential to the invention and can be appropriately selected or omitted without departing from the spirit of the invention.

[0084] List of reference numerals

[0085] 1: Steering system 2: Vehicle

[0086] 3: Front wheel 10: Steering input mechanism

[0087] 11: Steering mechanism 12: Steering actuator

[0088] 13: Reaction force actuator 15: Control unit

[0089] 18: Steering shaft 19: Steering wheel

[0090] 20: Steering column 21: Steering angle sensor

[0091] 32: Steering angle sensor; 37: Steering center setting switch.

[0092] 39: Vehicle diagnostic device; 43: Physical stopper

[0093] α: Turning angle; αt: Target turning angle

[0094] β: Steering angle; βmP: Maximum physical steering angle

[0095] βmC: Controls the maximum steering angle; T: Reaction torque.

[0096] TSL: Steering Limiting Reaction Torque; Tt: Target Reaction Torque

Claims

1. A steering system for a vehicle, the steering system for a vehicle comprising: A steering wheel configured to be operated by a driver; A steering shaft connected to the steering wheel in a rotational motion transmission manner; A steering mechanism, mechanically separated from the steering shaft and configured to steer the wheels of the vehicle; A steering angle sensor that detects the steering angle about the control steering center as the angular position of the steering axis corresponding to the straight-ahead state of the vehicle; A steering actuator that provides driving force to the steering mechanism; A steering angle sensor that detects the steering angle of the wheel; A reaction force actuator that applies a reaction force to the steering wheel in response to a steering operation; as well as A control unit is configured to determine a target steering angle based on the steering angle and drive the steering actuator to make the steering angle match the target steering angle, and to determine a target reaction force based on the steering state of the wheels and drive the reaction force actuator to make the reaction force match the target reaction force. The control unit is configured to correct the output of the steering angle sensor upon receiving a specified input, such that the current steering angle corresponds to the control steering center. The control unit is configured to: correct the output of the steering angle sensor when a predetermined time period has elapsed since the moment the specified input was received, and temporarily stop driving the reaction force actuator before the predetermined time period has elapsed since the moment the specified input was received.

2. A steering system for a vehicle, the steering system for a vehicle comprising: A steering wheel configured to be operated by a driver; A steering shaft connected to the steering wheel in a rotational motion transmission manner; A steering mechanism, mechanically separated from the steering shaft and configured to steer the wheels of the vehicle; A steering angle sensor that detects the steering angle about the control steering center as the angular position of the steering axis corresponding to the straight-ahead state of the vehicle; A steering actuator that provides driving force to the steering mechanism; A steering angle sensor that detects the steering angle of the wheel; A reaction force actuator that applies a reaction force to the steering wheel in response to a steering operation; as well as A control unit is configured to determine a target steering angle based on the steering angle and drive the steering actuator to make the steering angle match the target steering angle, and to determine a target reaction force based on the steering state of the wheels and drive the reaction force actuator to make the reaction force match the target reaction force. The control unit is configured to correct the output of the steering angle sensor upon receiving a specified input, such that the current steering angle corresponds to the control steering center. The control unit is configured to: correct the output of the steering angle sensor when a predetermined time period has elapsed since the moment the specified input is received, and temporarily reduce the target reaction force before the predetermined time period has elapsed since the moment the specified input is received.

3. A steering system for a vehicle, the steering system for a vehicle comprising: A steering wheel configured to be operated by a driver; A steering shaft connected to the steering wheel in a rotational motion transmission manner; A steering mechanism, mechanically separated from the steering shaft and configured to steer the wheels of the vehicle; A steering angle sensor that detects the steering angle about the control steering center as the angular position of the steering axis corresponding to the straight-ahead state of the vehicle; A steering actuator that provides driving force to the steering mechanism; A steering angle sensor that detects the steering angle of the wheel; A reaction force actuator that applies a reaction force to the steering wheel in response to a steering operation; as well as A control unit is configured to determine a target steering angle based on the steering angle and drive the steering actuator to make the steering angle match the target steering angle, and to determine a target reaction force based on the steering state of the wheels and drive the reaction force actuator to make the reaction force match the target reaction force. The control unit is configured to correct the output of the steering angle sensor upon receiving a specified input, such that the current steering angle corresponds to the control steering center. The control unit is configured to: determine the target reaction force based on the deviation between the target steering angle and the steering angle; correct the output of the steering angle sensor when a predetermined time period has elapsed since the moment the specified input is received; and set a dead zone in the deviation before the predetermined time period has elapsed since the moment the specified input is received.

4. A steering system for a vehicle, the steering system for a vehicle comprising: A steering wheel configured to be operated by a driver; A steering shaft connected to the steering wheel in a rotational motion transmission manner; A steering mechanism, mechanically separated from the steering shaft and configured to steer the wheels of the vehicle; A steering angle sensor that detects the steering angle about the control steering center as the angular position of the steering axis corresponding to the straight-ahead state of the vehicle; A steering actuator that provides driving force to the steering mechanism; A steering angle sensor that detects the steering angle of the wheel; A reaction force actuator that applies a reaction force to the steering wheel in response to a steering operation; as well as A control unit is configured to determine a target steering angle based on the steering angle and drive the steering actuator to make the steering angle match the target steering angle, and to determine a target reaction force based on the steering state of the wheels and drive the reaction force actuator to make the reaction force match the target reaction force. The control unit is configured to correct the output of the steering angle sensor upon receiving a specified input, such that the current steering angle corresponds to the control steering center. The steering system for the vehicle also includes a physical stop that defines the physical maximum steering angle of the steering shaft in each rotational direction, and The control unit is configured to limit the maximum controlled steering angle (βmC) of the steering wheel in each rotational direction starting from the control steering center, the maximum controlled steering angle being less than the physical maximum steering angle, and the control unit is configured to drive the reaction force actuator to generate a steering limiting reaction force (Tsl) that limits the maximum controlled steering angle. Specifically, when the specified input is received with the steering wheel set to its geometric steering center, and it is determined that the maximum control steering angle will exceed the physical maximum steering angle, the control unit prohibits the correction of the steering angle sensor output.

5. A steering system for a vehicle, the steering system for a vehicle comprising: A steering wheel configured to be operated by a driver; A steering shaft connected to the steering wheel in a rotational motion transmission manner; A steering mechanism, mechanically separated from the steering shaft and configured to steer the wheels of the vehicle; A steering angle sensor that detects the steering angle about the control steering center as the angular position of the steering axis corresponding to the straight-ahead state of the vehicle; A steering actuator that provides driving force to the steering mechanism; A steering angle sensor that detects the steering angle of the wheel; A reaction force actuator that applies a reaction force to the steering wheel in response to a steering operation; as well as A control unit is configured to determine a target steering angle based on the steering angle and drive the steering actuator to make the steering angle match the target steering angle, and to determine a target reaction force based on the steering state of the wheels and drive the reaction force actuator to make the reaction force match the target reaction force. The control unit is configured to correct the output of the steering angle sensor upon receiving a specified input, such that the current steering angle corresponds to the control steering center. The steering system for the vehicle also includes a physical stop that defines the physical maximum steering angle of the steering shaft in each rotational direction, and The control unit is configured to limit the maximum controlled steering angle (βmC) of the steering wheel in each rotational direction starting from the control steering center, the maximum controlled steering angle being less than the physical maximum steering angle, and the control unit is configured to drive the reaction force actuator to generate a steering limiting reaction force (Tsl) that limits the maximum controlled steering angle. When the specified input is received with the steering wheel set to its geometric steering center, and it is determined that the maximum control steering angle will exceed the physical maximum steering angle, the control unit corrects the output of the steering angle sensor so that the current steering angle is as close as possible to the control steering center, without causing the maximum control steering angle to exceed the physical maximum steering angle.

6. A steering system for a vehicle, the steering system for a vehicle comprising: A steering wheel configured to be operated by a driver; A steering shaft connected to the steering wheel in a rotational motion transmission manner; A steering mechanism, mechanically separated from the steering shaft and configured to steer the wheels of the vehicle; A steering angle sensor that detects the steering angle about the control steering center as the angular position of the steering axis corresponding to the straight-ahead state of the vehicle; A steering actuator that provides driving force to the steering mechanism; A steering angle sensor that detects the steering angle of the wheel; A reaction force actuator that applies a reaction force to the steering wheel in response to a steering operation; as well as A control unit is configured to determine a target steering angle based on the steering angle and drive the steering actuator to make the steering angle match the target steering angle, and to determine a target reaction force based on the steering state of the wheels and drive the reaction force actuator to make the reaction force match the target reaction force. The control unit is configured to correct the output of the steering angle sensor when it receives a specified input, so that the current steering angle corresponds to the control steering center. The steering system for the vehicle also includes a physical stop that defines the physical maximum steering angle of the steering shaft in each rotational direction, and The control unit is configured to limit the maximum controlled steering angle (βmC) of the steering wheel in each rotational direction starting from the control steering center, the maximum controlled steering angle being less than the physical maximum steering angle, and the control unit is configured to drive the reaction force actuator to generate a steering limiting reaction force (Tsl) that limits the maximum controlled steering angle. When the specified input is received when the steering wheel is set to its geometric steering center, and it is determined that the maximum control steering angle will exceed the physical maximum steering angle, the control unit corrects the output of the steering angle sensor so that the geometric steering center of the steering wheel is aligned with the control steering center of the steering shaft, and changes the ratio of the steering angle to the steering angle to a smaller value so that the maximum control steering angle does not exceed the physical maximum steering angle.

7. The steering system for a vehicle according to any one of claims 1 to 6, the steering system for a vehicle further comprising a control steering center setting switch disposed in the vehicle for generating the predetermined input.

8. The steering system for a vehicle according to any one of claims 1 to 6, wherein, The specified input is from a vehicle diagnostic device that is detachably connected to the vehicle.

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