Vehicle and vehicle control method

Abstract

This disclosure relates to vehicles and vehicle control methods. The vehicle of the present invention includes a steering mechanism, a torque sensor, and an electronic control unit. The steering mechanism includes a rack and pinion, a steering shaft, and a steering actuator having an electric motor connected to the rack and pinion or the steering shaft via a motion conversion mechanism. A torque sensor is mounted on the steering shaft to detect the driver's steering torque. When the torque detected by the torque sensor exceeds a torque threshold during the execution of automatic steering control of the wheels, the electronic control unit switches from steering the wheels based on automatic steering control to steering the wheels at least based on the driver's steering operation. The torque threshold is adjusted according to the temperature of the motion conversion mechanism.

Description

Technical Field

[0001] This disclosure relates to vehicles and vehicle control methods. Background Technology

[0002] Japanese Patent Application Publication No. 2010-188854 discloses a lane keeping assist device. This lane keeping assist device performs a first steering angle control that prioritizes lane following when no steering intention is detected, and a second steering angle control that easily reflects the driver's steering operation when a steering intention is detected. The presence or absence of steering intention is determined based on the deviation between steering torque and steering angle.

[0003] If it is determined that a steering operation intervention by the driver has been performed, a switch is executed from steering of the wheels based on "automatic steering operation control" that does not require steering operation by the driver to steering of the wheels based on steering operation by at least the driver.

[0004] In the aforementioned automatic steering control, the torque sensor used to determine the presence or absence of steering intervention (steering control meaning) based on the driver's steering torque can experience variations in output torque even when the driver's hands are not on the steering wheel, for example, due to external disturbances from the road surface. Furthermore, the output torque value based on these factors can change due to the temperature characteristics of the frictional and viscous components of the steering mechanism. If the torque threshold is set uniformly regardless of temperature and these output torque values ​​are ignored, the following problems arise: Firstly, at the same low torque threshold, false determinations of steering intervention occur. Secondly, at the same high torque threshold, it is difficult to convert the control state so that the wheel steering reflects the driver's steering operation. Summary of the Invention

[0005] This disclosure was made in view of the aforementioned issues, and its purpose is to achieve both the ease of driver intervention in automatic steering control vehicles and the convenience of control state transitions.

[0006] The vehicle disclosed herein includes a steering control device, a torque sensor, and an electronic control unit. The steering control device includes a rack and pinion shaft connected to the wheels, a steering control shaft connecting the steering wheel to the rack and pinion shaft, and a steering actuator having an electric motor connected to the rack and pinion shaft or the steering control shaft via a motion conversion mechanism. A torque sensor is mounted on the steering control shaft to detect the driver's steering torque. When the torque detected by the torque sensor exceeds a torque threshold during the execution of automatic steering control of the wheels, the electronic control unit switches from steering the wheels based on automatic steering control to steering the wheels at least based on the driver's steering operation. The torque threshold is adjusted according to the temperature of the motion conversion mechanism.

[0007] The vehicle control method disclosed herein controls a vehicle equipped with a steering mechanism and a torque sensor. The steering mechanism includes a rack shaft connected to the wheels, a steering shaft connecting a steering wheel to the rack shaft, and a steering actuator having an electric motor connected to the rack shaft or the steering shaft via a motion conversion mechanism. A torque sensor is mounted on the steering shaft to detect the driver's steering torque. The vehicle control method includes: switching steering of the wheels from based on the automatic steering control to based at least on steering operations performed by the driver when the torque detected by the torque sensor exceeds a torque threshold during the execution of automatic steering control of the wheels; and changing the torque threshold according to the temperature of the motion conversion mechanism.

[0008] According to this disclosure, the torque threshold can be appropriately set considering the temperature characteristics of the frictional and viscous components of the motion conversion mechanism included in the steering actuator of the steering control device. As a result, compared with examples where the torque threshold is set the same regardless of the temperature, it is possible to achieve both a low risk of misjudgment of steering intervention and a control state that facilitates transition to a non-automatic control state (at least a state where the wheels are steered based on the steering operation performed by the driver), where the steering torque is actually applied to the steering axis by the driver. Attached Figure Description

[0009] The features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, in which the same reference numerals denote the same elements, wherein,

[0010] Figure 1 This is a diagram illustrating an example of the configuration of a vehicle involved in the implementation method.

[0011] Figure 2 This is a block diagram showing the functional structure of the ECU related to the steering control calculations involved in the implementation method.

[0012] Figure 3 This is a graph illustrating an example of the relationship between temperature T and torque threshold X.

[0013] Figure 4 It is a flowchart illustrating the process related to the determination of steering intervention in the implementation method and the transition of steering state based on the determination of steering intervention.

[0014] Figure 5 This is a diagram used to illustrate variations related to the setting of the torque threshold X involved in this disclosure. Detailed Implementation

[0015] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. However, when the number, quantity, quantity, range, etc. of each element are mentioned in the embodiments shown below, the technical concept involved in the present disclosure is not limited to the number mentioned therein, unless specifically stated otherwise or clearly specified in principle.

[0016] 1. Example of vehicle structure

[0017] Figure 1 This is a diagram illustrating an example of the structure of vehicle 1 according to the embodiment. (See diagram below.) Figure 1 As shown, vehicle 1 is equipped with a steering control device 10. The steering control device 10 is a device for steering the wheels 2. The steering control device 10 includes a steering wheel 12, a steering control shaft 14, and a steering unit 16.

[0018] The steering wheel 12 is used for steering operations performed by the driver. The first end of the steering control shaft 14 is connected to the steering wheel 12. The second end of the steering control shaft 14 is connected to the rack shaft (steering shaft) 20 included in the steering unit 16 via a pinion 18.

[0019] The steering unit 16, in addition to the aforementioned pinion 18 and rack shaft 20, also includes a rack housing 22, a pair of tie rods 24, and a steering actuator 26.

[0020] The pinion 18 and rack shaft 20 are disposed within the rack housing 22. The rack shaft 20 meshes with the pinion 18. Both ends of the rack shaft 20 are connected to the wheel 2 via a tie rod 24 and a steering knuckle (not shown). The rotation of the steering wheel 12 is transmitted to the pinion 18 via the steering control shaft 14. The rotational motion of the pinion 18 is converted into linear motion of the rack shaft 20. As a result, the steering angle of the wheel 2 changes.

[0021] Steering actuator 26 generates a force that steers wheel 2. Steering actuator 26 includes an electric motor 28 and a motion conversion mechanism 30, and, for example, includes a belt mechanism 32. Electric motor 28 is connected to rack shaft 20 via belt mechanism 32 and motion conversion mechanism 30. Motion conversion mechanism 30, for example, is a ball screw mechanism housed within rack housing 22. The torque of electric motor 28 is transmitted to motion conversion mechanism 30 via belt mechanism 32. Motion conversion mechanism 30 converts the rotational motion of rotor of electric motor 28 into linear motion of rack shaft 20. As a result, the steering angle of wheel 2 changes.

[0022] The steering actuator 26 serves as an electric power steering (EPS) device that assists in steering operations performed by the driver. Additionally, the steering actuator 26 serves as an actuator for controlling the steering angle of the wheels 2 during the execution of "automatic steering control" (described later), where steering operations by the driver are not required.

[0023] Additionally, vehicle 1 includes an electronic control unit (ECU) 40. The ECU 40 controls the steering actuator 26. Specifically, the ECU 40 includes a processor 42, a storage device 44, and an input / output interface. The input / output interface acquires sensor signals from sensors installed in vehicle 1 and outputs operating signals to the steering actuator 26. The processor 42 performs various processes related to the control of the steering actuator 26. The storage device 44 stores various programs and data (including mappings) for the processes performed by the processor 42. The processor 42 reads and executes programs from the storage device 44, thereby realizing the processes performed by the ECU 40. Furthermore, there may be multiple ECUs 40.

[0024] The aforementioned sensor class includes, for example, various sensors required for the execution of automatic steering control (e.g., sensors such as cameras that identify the surroundings of vehicle 1), as well as a torque sensor 46, a rotation angle sensor 48, a temperature sensor 50, and a current sensor 52. Specifically, the torque sensor 46 is mounted on the steering shaft 14 to detect (infer) the torque acting on the steering shaft 14, i.e., the steering torque, when the driver rotates the steering wheel 12. The torque sensor 46 detects the torque TR acting on the torsion bar, which is part of the steering shaft 14. The rotation angle sensor 48 detects the rotation angle of the electric motor 28. The temperature sensor 50, for example, is mounted on the rack housing 22 to detect (infer) the temperature T of the motion conversion mechanism 30. The current sensor 52 detects the output current (drive current) of the steering actuator 26.

[0025] Another configuration example of the steering actuator

[0026] In addition, Figure 1In the example shown, the steering actuator 26 is disposed on the rack shaft 20, which performs linear motion, in the force transmission path between the steering wheel 12 and the wheel 2. However, the "steering actuator" disclosed herein can also be disposed on the steering control shaft 14, which performs rotational motion (another structural example A). In this other structural example A, a motion conversion mechanism between the electric motor included in the steering actuator and the steering control shaft 14 converts the rotational motion of the electric motor rotor into the rotational motion of the steering control shaft 14, for example, a gear mechanism such as a worm gear mechanism. In addition, in this other structural example A, a torque sensor for detecting the driver's steering torque is disposed on the steering control shaft 14 at the portion between the steering wheel 12 and the aforementioned electric motor (e.g., a torsion bar).

[0027] 2. Steering control

[0028] The steering control performed by the ECU40 using the steering actuator 26 includes torque assist control for assisting steering control performed by the driver, as well as "automatic steering control".

[0029] Automatic steering control automatically steers vehicle 1 without requiring steering input from the driver. For example, after the driver receives an execution request for automatic steering control from an HMI (Human Machine Interface) device such as an operation button, the ECU 40 executes automatic steering control based on the fulfillment of specified execution conditions. Automatic steering control is executed whether the driver's hands are off the steering wheel 12 or on the steering wheel 12.

[0030] Specifically, automatic steering control includes, for example, the automatic operation control of various driving operations such as vehicle acceleration, deceleration, and steering. In automatic steering control, ECU 40 controls steering actuator 26 (electric motor 28) to generate steering torque for bringing the steering angle of wheel (steering wheel) 2 close to a target steering angle. Alternatively, automatic steering control can be performed without the automatic control of at least one of the driving operations of acceleration and deceleration.

[0031] Hereinafter, the steering control state in which automatic steering control is performed will be referred to as the "automatic control state," and the steering control state that is not solely based on automatic steering control will be referred to as the "non-automatic control state." In the non-automatic control state, the steering of the wheels 2 is basically accompanied by torque assist control and is based on the steering operation performed by the driver. Furthermore, the non-automatic control state is a state in which the steering of the wheels 2 is based at least on the steering operation performed by the driver. Therefore, in the non-automatic control state, instead of the example based solely on the steering operation performed by the driver, the steering of the wheels 2 can be performed through the cooperation of the steering operation performed by the driver and the automatic steering operation utilizing the steering actuator 26.

[0032] When driver intervention is detected during automatic steering control, a transition from automatic to non-automatic control is initiated. This steering intervention detection is performed using the aforementioned torque sensor 46. Specifically, steering intervention is detected when the driver's steering torque exceeds a predetermined torque threshold X.

[0033] A torque sensor 46 is used to obtain the steering torque used in determining steering intervention. That is, a torque sensor 46 is provided to obtain the driver's steering torque. When a steering operation is performed by the driver, the torque TR detected by the torque sensor 46 is substantially equivalent to the driver's steering torque.

[0034] Here, the torque sensor 46 described above can output a torque value even when the driver's hands are not on the steering wheel 12, for example, due to external disturbances from the road surface. More specifically, the input from the road surface caused by this external disturbance (e.g., unevenness of the road surface) acts on the rack shaft 20 via the wheel 2 and tie rod 24. If the rack shaft 20 moves due to this input, a torsional torque is generated on the steering control shaft 14, which is then input from the rack shaft 20 to the steering control shaft 14 via the pinion 18. As a result, the torque sensor 46 may output a torque value even when the driver's hands are off the steering wheel 12.

[0035] Furthermore, due to the aforementioned reasons, the output torque value will also change due to the temperature characteristics of the frictional and viscous components of the steering control device 10. More specifically, this torque value changes due to the temperature characteristics of the frictional and viscous components (the viscous components of the lubricating oil) of the motion conversion mechanism (e.g., a ball screw mechanism) 30, which is movable between the electric motor 28 and the rack shaft 20. If the torque threshold X is set uniformly regardless of the temperature T of the motion conversion mechanism 30, regardless of the output torque value, the following problems arise: That is, when the same torque threshold X is low, a misjudgment of steering intervention occurs. On the other hand, when the same torque threshold X is high, it is difficult to switch to a control state where the steering of the wheels reflects the driver's steering operation.

[0036] Furthermore, the same problem arises in a structure, such as the above-described structural example A, in which a motion conversion mechanism (e.g., a gear mechanism) is arranged between the electric motor included in the steering actuator and the steering control shaft 14.

[0037] In view of the above-mentioned issues, the steering intervention determination and the steering state transition based thereon in this embodiment are performed as follows. Figure 2 This is a block diagram illustrating the functional structure of the ECU 40 related to the steering control calculations involved in the embodiment. The ECU 40 includes a steering torque estimation unit 54, a temperature estimation unit 56, a steering intervention determination unit 58, and a control state transition unit 60. Furthermore, in Figure 2 In one example shown, the steering torque inference unit 54, temperature inference unit 56, steering intervention determination unit 58, and control state transition unit 60 are provided by one ECU 40, but they can also be provided by multiple ECUs respectively.

[0038] The steering torque inference unit 54 uses the torque sensor 46 to detect the torque TR and infers the detected torque TR as the steering torque.

[0039] The temperature inference unit 56 uses the temperature sensor 50 to detect the temperature and infers the detected temperature as the temperature T of the motion conversion mechanism 30. As described above, the temperature sensor 50 is mounted on the rack housing 22. However, the location of the temperature sensor 50 used for inferring the temperature T is not limited to the rack housing 22.

[0040] That is, the temperature sensor 50 can be placed in any location where the temperature related to temperature T can be obtained, or where temperature T can be inferred. Therefore, the temperature sensor 50 can also be installed, for example, around the motor 28 located around the motion conversion mechanism 30.

[0041] Furthermore, the steering unit 16, including the steering actuator 26, is disposed in a space (more specifically, for example, a compartment housing transmission components such as an internal combustion engine) 64 located outside the vehicle compartment 62 of the vehicle 1 and exposed to the outside air. Therefore, the temperature sensor 50 can also be configured to detect the temperature of this space 64 (in other words, the ambient temperature around the motion conversion mechanism 30) as temperature T. And, for the deduction of temperature T, the signal of the current sensor 52 can also be used, for example, along with the signal of the temperature sensor 50.

[0042] Furthermore, in another structural example A described above, the motion conversion mechanism is disposed within the carriage 62. Therefore, the temperature sensor for inferring temperature T in another structural example A can also be configured to detect the temperature inside the carriage 62, which corresponds to the ambient temperature surrounding the motion conversion mechanism.

[0043] During the execution of automatic steering control, the steering intervention determination unit 58 compares the torque TR, which is obtained as the steering torque by the steering torque inference unit 54, with the torque threshold X. Furthermore, if the absolute value of the torque TR exceeds the torque threshold X, the steering intervention determination unit 58 determines that the driver has intervened in steering.

[0044] In this embodiment, the torque threshold X used in determining steering intervention is not the same regardless of the temperature T of the motion conversion mechanism 30, but changes according to the temperature T. Specifically, the torque threshold X is higher when the temperature T is lower than when the temperature T is higher.

[0045] Figure 3 This is a graph illustrating an example of the relationship between temperature T and the torque threshold X. In Figure 3 In one example, it is set that the lower the temperature T, the higher the torque threshold X; in other words, the higher the temperature T, the lower the torque threshold X. Additionally, in Figure 3 In one example shown, the torque threshold X changes linearly with respect to temperature T, but it can also be set to change curvilinearly.

[0046] If the steering intervention determination unit 58 determines that steering intervention has been performed, the control state transition unit 60 changes the steering state from automatic control state to non-automatic control state.

[0047] Figure 4 This is a flowchart illustrating the process related to the determination of steering intervention and the transition of steering state based on the determination of steering intervention, as described in the embodiment. The ECU 40 (processor 42) repeatedly executes the processing shown in this flowchart while the vehicle 1 is in motion.

[0048] exist Figure 4In step S100, the ECU40 determines whether automatic steering control is being executed. If the determination is negative, the process proceeds to the return step. Conversely, if the determination is positive, the process proceeds to step S102.

[0049] In step S102, the ECU40 (steering torque inference unit 54) uses the torque sensor 46 to detect the torque TR and infers the detected torque TR as the steering torque.

[0050] Next, in step S104, the ECU40 (temperature inference unit 56) uses the temperature sensor 50 to detect the temperature, and infers the detected temperature as the temperature T of the motion conversion mechanism 30.

[0051] Next, in step S106, the ECU 40 (steering intervention determination unit 58) calculates the torque threshold X. The storage device 44 of the ECU 40 stores the relationship between temperature T and torque threshold X (e.g., Figure 3 This is stored as a mapping. The ECU40 calculates the torque threshold X corresponding to temperature T based on such a mapping. Alternatively, this relationship can also be stored as a formula.

[0052] Next, in step S108, the ECU40 (steering intervention determination unit 58) determines whether the absolute value of the torque TR inferred in step S102 exceeds the torque threshold X calculated in step S106.

[0053] If the determination result in step S108 is negative (torque |TR|≤torque threshold X), that is, if it is determined that no driver steering intervention has been performed, the process proceeds to the return step. That is, automatic steering control continues. On the other hand, if the determination result is positive (torque |TR|>torque threshold X), that is, if it is determined that no steering intervention has been performed, the process proceeds to step S110.

[0054] In step S110, the ECU40 (control state transition unit 60) switches the steering control state from automatic control state to non-automatic control state.

[0055] 3. Effects

[0056] As explained above, according to this embodiment, the torque threshold X used to determine whether driver steering intervention has been performed is changed based on the temperature T of the motion conversion mechanism 30. Therefore, the torque threshold X can be appropriately set considering that the frictional and viscous components of the motion conversion mechanism 30 each have temperature characteristics. As a result, compared to examples where the torque threshold X is set the same regardless of temperature T, it is possible to achieve both a lower risk of false determinations of steering intervention and a smoother transition to a non-automatic control state, even when the driver's steering torque is actually applied to the steering shaft 14.

[0057] More specifically, generally speaking, the lower the temperature T, the greater the frictional and viscous components of the motion conversion mechanism 30, which functions as a ball screw mechanism. Therefore, when an input from the road surface, acting as an external disturbance, acts on the rack shaft 20, the motion conversion mechanism 30 is difficult to move if the temperature T is low. This situation functions in a way that hinders the movement of the rack shaft 20. However, when the temperature T is low, the torque input from the rack shaft 20 to the steering shaft 14 when the force acting on the rack shaft 20 from the road surface overcomes the resistance caused by the frictional and viscous components of the motion conversion mechanism 30 and the rack shaft 20 begins to move is more likely to become greater than when the temperature T is high. Therefore, according to this embodiment, when the temperature T is low, the torque threshold X is set higher than when the temperature T is high. Thus, the torque threshold X can be appropriately set taking into account the temperature characteristics of the frictional and viscous components of the motion conversion mechanism 30.

[0058] 4. Variations related to the setting of torque threshold X

[0059] For example, the torque threshold X, which varies with the temperature T of the motion conversion mechanism 30, can also be set as in the following variation.

[0060] Figure 5 This diagram illustrates a variation relating to the setting of the torque threshold X involved in this disclosure. In this variation, the temperature T region sequentially includes temperature region Ra, temperature region Rb, and temperature region Rc from the low-temperature side. Temperature region Ra is the region with a temperature value Ta above but below the temperature value Tb. Temperature region Rb is the region with a temperature value Tb above but below the temperature value Tc. Temperature region Rc is the region with a temperature value Tc above but below the temperature value Td. Furthermore, temperature value Ta represents an extremely low temperature (e.g., -30°C). Temperature value Tb represents a low temperature (e.g., 0°C). Temperature value Tc represents a normal temperature (e.g., 25°C). Temperature value Td represents a high temperature (e.g., 80°C).

[0061] In this modified example, a comparison between the temperature region Ra on the low-temperature side and the temperature region Rb on the adjacent high-temperature side shows that, as... Figure 5 As shown, the torque threshold X is higher in temperature region Ra than in temperature region Rb. Moreover, the rate of decrease of torque threshold X with increasing temperature T in temperature region Ra is greater than the rate of decrease of torque threshold X with increasing temperature T in temperature region Rb.

[0062] Similarly, in this modified example, a comparison between the temperature region Rb on the low-temperature side and the temperature region Rc on the high-temperature side adjacent to that region shows that, as Figure 5 As shown, the torque threshold X is higher in temperature region Rb than in temperature region Rc. Moreover, the rate of decrease of torque threshold X with increasing temperature T in temperature region Rb is greater than the rate of decrease of torque threshold X with increasing temperature T in temperature region Rc.

[0063] According to this modified example, the temperature characteristics of the frictional and viscous components of the motion conversion mechanism 30 can be taken into account more appropriately to set the torque threshold X corresponding to temperature T more appropriately.

[0064] Furthermore, in this modified example, in comparing temperature region Ra and temperature region Rb, temperature region Ra corresponds to an example of the "second temperature region" involved in this disclosure, and temperature region Rb corresponds to an example of the "first temperature region" involved in this disclosure. Additionally, in comparing temperature region Rb and temperature region Rc, temperature region Rb corresponds to another example of the "second temperature region" involved in this disclosure, and temperature region Rc corresponds to another example of the "first temperature region" involved in this disclosure.

[0065] In addition, Figure 5 In order to set the torque threshold X based on the temperature T, three consecutive temperature regions Ra, Rb, and Rc are used. However, the temperature regions used to set the torque threshold X can be two or more temperature regions, as long as the relationship between the "first temperature region" and the "second temperature region" mentioned above is satisfied.

Claims

1. A vehicle, wherein, This vehicle is equipped with: A steering control device includes a rack shaft connected to a wheel, a steering control shaft connecting a steering wheel to the rack shaft, and a steering actuator having an electric motor connected to the rack shaft or the steering control shaft via a motion conversion mechanism. A torque sensor is mounted on the steering shaft to detect the driver's steering torque; as well as The electronic control unit, when the torque detected by the torque sensor exceeds a torque threshold during the execution of the automatic steering control of the wheels, switches from steering the wheels based on the automatic steering control to steering the wheels based at least on steering operations performed by the driver. The torque threshold is changed according to the temperature of the motion conversion mechanism. The temperature range includes a first temperature range and a second temperature range that is at a lower temperature compared to the first temperature range. Compared to the first temperature region, the torque threshold in the second temperature region is higher. The rate of decrease of the torque threshold relative to the increase of temperature in the second temperature region is greater than the rate of decrease of the torque threshold relative to the increase of temperature in the first temperature region.

2. A vehicle control method, which is a vehicle control method for controlling a vehicle, wherein the vehicle comprises: A steering control device includes a rack shaft connected to a wheel, a steering control shaft connecting a steering wheel to the rack shaft, and a steering actuator having an electric motor connected to the rack shaft or the steering control shaft via a motion conversion mechanism. and A torque sensor is mounted on the steering shaft to detect the driver's steering torque. in, The vehicle control method includes: When the torque detected by the torque sensor exceeds a torque threshold during the execution of the automatic steering control of the wheels, the steering of the wheels is switched from being based on the automatic steering control to being based at least on steering operations performed by the driver; and The torque threshold is adjusted according to the temperature of the motion conversion mechanism. in, The temperature range includes a first temperature range and a second temperature range that is at a lower temperature compared to the first temperature range. Compared to the first temperature region, the torque threshold in the second temperature region is higher. The rate of decrease of the torque threshold relative to the increase of temperature in the second temperature region is greater than the rate of decrease of the torque threshold relative to the increase of temperature in the first temperature region.

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