Steering system

Abstract

The present application provides an electric power steering type steering system which enables a driver to easily and intuitively perceive a control mode switching. The present application is provided with: an operation unit (2) including an operation member (20) and a reaction force applying device (25); a steering unit (3) which is mechanically separated from the operation unit (2) and steers a wheel in accordance with a steering current supplied; and a controller (4) which controls the steering unit (3) and the reaction force applying device (25) based on an operation signal and a steering angle signal, a plurality of control modes which respectively realize different steering characteristics are set in the controller (4), the controller (4) is configured to execute one or more of a plurality of characteristic changing controls after determining that a vehicle state satisfies a prescribed condition in accordance with a control mode switching, and to execute one or more of other characteristic changing controls regardless of whether the vehicle state satisfies the prescribed condition.

Description

Technical Field

[0001] This invention relates to a vehicle steering system. Background Technology

[0002] Vehicle steering systems often feature multiple control modes (driving modes) with different operating characteristics. In such systems, the control mode is switched based on the driver's input. For example, the electric power steering system described in International Publication No. 2011 / 048772 is configured to gradually change the control value during mode switching, with the switching period varying depending on the control mode before and after the switch. This allows the driver to easily perceive the change in control mode.

[0003] Patent Document 1: International Publication No. 2011 / 048772

[0004] On the other hand, electric steering systems mechanically separate the driver-operated control unit from the steering unit that turns the wheels. In such electric steering systems, the challenge lies in enabling the driver to intuitively perceive the switching of control modes more effectively. Summary of the Invention

[0005] The steering system of the present invention is an electric steering system, comprising: an operating unit including an operating component for steering operations performed by a driver and a reaction force applying device for applying an operating reaction force to the operating component; a steering unit mechanically separated from the operating unit, which steers the wheels according to a supplied steering current; and a controller that controls the steering unit and the reaction force applying device based on an operating signal received from the operating unit related to the operation of the operating component and a steering angle signal received from the steering unit related to the actual steering angle of the wheels. The controller has multiple control modes, each achieving different steering characteristics. The controller is configured to change the steering characteristics by executing multiple characteristic-changing controls that change predetermined control constants related to the control of the reaction force applying device and / or the steering unit, depending on the switching of the control modes. The controller is configured to execute one or more of the multiple characteristic-changing controls after determining that the vehicle state meets predetermined conditions, and to execute one or more other characteristic-changing controls regardless of whether the vehicle state meets the predetermined conditions.

[0006] According to the structure of the present invention, when the driver switches the control mode, the determination of whether the vehicle state meets the prescribed conditions is not performed, but at least one characteristic change control is executed. That is, at least one characteristic related to steering responds quickly to the driver's switching operation of the control mode and begins to change. As a result, the driver can perceive the switching of the control mode more strongly and intuitively. Attached Figure Description

[0007] Figure 1 This is a structural diagram of the steering system in this embodiment.

[0008] Figure 2 This is a timing diagram used to illustrate an example of switching control modes in this embodiment.

[0009] Figure 3 This is a flowchart illustrating the process of switching control modes in this embodiment.

[0010] Explanation of reference numerals in the attached figures

[0011] 1…Steering system, 2…Operating unit, 20…Operating component, 25…Reaction force application device, 3…Steering unit, 4…Controller. Detailed Implementation

[0012] As an example, the steering system 1 in this embodiment is mounted on an electric vehicle. In-vehicle communication is conducted, for example, via CAN (car area network or controllable area network), FlexRay, or Ethernet.

[0013] like Figure 1 As shown, the steering system 1 includes an operating unit 2, a steering unit 3, and a controller 4. In this embodiment, the operating unit 2 includes an operating component 20, a steering shaft 21, a steering column 22, an operating quantity sensor 23, an operating torque sensor 24, and a reaction force application device 25.

[0014] The operating component 20 is a handle-operated component for the driver to perform steering operations, such as a steering wheel. Furthermore, the shape of the operating component 20 is not limited to a circle like a steering wheel; it can also be a polygonal shape, such as a quadrilateral shape. The operating component 20 is fixed to the front end of the steering shaft 21. The operating component 20 and the steering shaft 21 are held rotatably by the instrument panel reinforcement via the steering column 22.

[0015] The operation amount sensor 23 is a sensor that detects the operation amount (operation angle) of the operating component 20. The operating torque sensor 24 is a sensor that detects the operating torque of the operating component 20. For example, the operating torque sensor 24 detects the amount of torsion of the torsion bar 27 assembled on the steering shaft 21.

[0016] The reaction force applying device 25 is a device that applies an operating reaction force to the operating member 20. The reaction force applying device 25 includes a reaction force motor 26, which is an electric motor. Powered by the reaction force motor 26 supported by the steering column 22, the reaction force applying device 25 applies an operating reaction force to the steering shaft 21 for steering operations to the operating member 20. The reaction force applying device 25 is a device with a typical structure including a reducer, etc. A rotation angle sensor 26a is provided in the reaction force motor 26.

[0017] Steering unit 3 is a device that steers wheels 11 and 12. Steering unit 3 is mechanically separated from operating unit 2. Steering unit 3 includes: steering rod 31, housing 32, rod moving mechanism 33, steering motor 35, current sensor 351, rotation angle sensor 352, and steering angle sensor 36.

[0018] The steering rod 31 is a component whose two ends are connected to the left and right steering knuckles 90 respectively via steering tie rods 34. The housing 32 is a component that supports the steering rod 31 so that it can move left and right and is fixedly held in the vehicle body.

[0019] The lever movement mechanism 33 is a mechanism that uses the steering motor 35 as a drive source to move the steering lever 31 left and right. The steering motor 35 is an electric motor that steers the wheels 11 and 12. The lever movement mechanism 33 is mainly composed of a ball screw mechanism that includes a ball groove provided in the steering lever 31 and a nut screwed into the ball groove. The steering motor 35 rotates the nut.

[0020] The current sensor 351 is a sensor that detects the current value of the control current, i.e., the steering current, input to the steering motor 35. The rotation angle sensor 352 is a sensor that detects the rotation angle of the steering motor 35. The steering angle sensor 36 is a sensor that detects the steering angle (steering amount) of the wheels 11 and 12. The steering angle sensor 36 detects the amount of movement to the left and right respectively from the neutral position of the steering lever 31.

[0021] The controller 4 is configured to control the steering unit 3 and the reaction force application device 25 based on the operation signals received from the operation unit 2 related to the action of the operation component 20. The controller 4 is configured to receive steering angle signals related to the steering angle of the wheels 11 and 12, i.e., the detection values ​​of the steering angle sensor 36, from the steering unit 3. The controller 4 controls the steering unit 3 and the reaction force application device 25 based on the operation signals and the steering angle signals.

[0022] The controller 4 is a computer equipped with one or more processors 41 and one or more memories 42. The computer may also be referred to as an electronic control unit (ECU). The controller 4 is communicatively connected to the operating unit 2 and the steering unit 3. The operating unit 2 and the steering unit 3 are electrically connected via communication lines and the controller. Thus, the steering system 1 is an electric steering system. Furthermore, the controller 4 may also be composed of two or more computers communicatively connected. For example, the controller 4 may also consist of an operating ECU located in the operating unit 2 and a steering ECU located in the steering unit 3.

[0023] The controller 4 calculates the steering gear ratio (hereinafter referred to as "gear ratio") based on the prescribed gear ratio calculation rules and the vehicle speed. The gear ratio is the ratio of the steering amount (steering angle) of the wheels 11 and 12 to the operating amount (operating angle) of the operating component 20. The gear ratio calculation rules are rules that represent the relationship between vehicle speed and gear ratio, such as a mapping table. The vehicle speed is calculated based on the detection values ​​of the wheel speed sensors 70 installed on each wheel.

[0024] Controller 4 calculates the transmission ratio based on the transmission ratio calculation rules and vehicle speed. The transmission ratio is variable according to vehicle speed. The transmission ratio calculation rules are set to, for example, increase at low speeds and decrease at high speeds. Based on the calculated transmission ratio, vehicle speed, operating signal, and steering angle signal, controller 4 calculates the target steering angle for wheels 11 and 12. Controller 4 supplies the steering current corresponding to the target steering angle to steering motor 35. The transmission ratio and target steering angle vary according to the vehicle speed.

[0025] An example of calculating the operating reaction force applied by the reaction force applying device 25 will be explained. As an example, the operating reaction force is calculated based on the angular axial force value and the current axial force value. The controller 4 calculates the angular axial force value based on the vehicle speed and the target steering angle. The angular axial force value can be referred to as the force simulating the self-centering torque, for example. When the vehicle speed is below a specified value, the angular axial force value dedicated to low speed is set as the angular axial force value.

[0026] Controller 4 calculates the current axial force value based on changes in the steering current, unlike the angular axial force value. For example, when a vehicle is traveling on an uneven road surface, the actual steering angle changes, creating an angle difference between the target steering angle and the actual steering angle. This angle difference causes a change in the steering current. This is because the steering load varies according to road conditions. The current axial force value corresponds to the change in steering current and reflects the road conditions. The operating reaction force is calculated based on a predetermined or variable mixing ratio, using a mixture of the angular axial force value and the current axial force value.

[0027] (Control Mode)

[0028] The controller 4 is configured with multiple control modes, each implementing different steering characteristics. These control modes are also referred to as driving modes. In the controller 4 of this embodiment, as an example, normal mode, sport mode, and comfort mode are provided. The control mode is changed according to the driver's (passenger's) operation. The steering characteristics of each control mode are different. The steering characteristics are set by several minor characteristics, such as the characteristics of the operating reaction force. As an example, the steering characteristics are set by the "amount of road information transmitted," the "magnitude of the operating reaction force relative to the amount of operation of the operating component 20," and the "magnitude of the wheel steering angle relative to the amount of operation of the operating component 20."

[0029] Controller 4 is configured to perform various characteristic change controls based on the switching of control modes, thereby changing the steering characteristics. Characteristic change control is control that changes a predetermined control constant related to the control of the reaction force application device 25 and / or the steering unit 3. In other words, characteristic change control is control that changes one of the multiple minor characteristics constituting the steering characteristics by changing a predetermined control constant. In characteristic change control, controller 4 gradually changes the control constant of the object being changed relative to the elapsed time (i.e., gradually changes the control constant). When characteristic change control is executed, the control constant of the object being changed is gradually changed from the set value in the control mode before the switch to the set value in the control mode after the switch. The period during which the control constant is gradually changed is also called the gradual change period.

[0030] Based on the switching of control modes, after determining that the vehicle state meets the specified conditions, controller 4 executes one or more characteristic change controls from a variety of characteristic change controls. Alternatively, based on the switching of control modes, controller 4 executes one or more characteristic change controls different from the above, regardless of whether the vehicle state meets the specified conditions.

[0031] Vehicle status is represented by the vehicle's driving state, such as speed, forward movement, or turning. Specified conditions are those related to speed and turning, such as "vehicle speed is below a specified speed" and / or "vehicle is moving forward."

[0032] According to this embodiment, when the driver switches the control mode, the determination of whether the vehicle state meets the prescribed conditions is not performed, but at least one characteristic change control is executed. That is, at least one minor characteristic responds quickly to the control mode switching operation and begins to change. This allows the driver to strongly and intuitively perceive the control mode switch. Furthermore, after confirming the vehicle state, the minor characteristic required for vehicle stability as specified in relation to the characteristic change is executed. Thus, by executing some characteristic change controls that do not require confirmation of the vehicle state based on the driver's mode switching operation, the driver's actual perception of the control mode switch can be improved.

[0033] The following specific examples illustrate the characteristic change control of this embodiment. In the controller 4 of this embodiment, three types of characteristic change control are provided: transmission change control, reaction force change control, and transmission ratio change control.

[0034] (Transfer of change control)

[0035] Transmission change control is a control that gradually changes the control constant related to the amount of road information transmitted to the operating component 20. Transmission change control can also be described as a control that gradually changes a predetermined control constant related to the control of the reaction force application device 25 in a manner consistent with the switched control mode. A delay limiter may also be used in the control (gradual change mechanism) that gradually changes the control constant.

[0036] In the transmission change control, the control constants for the changed object are the extraction band and the filter gain. Changes in the extraction band and the filter gain affect the axial force value of the operating reaction force. As mentioned above, the steering current varies according to the road surface unevenness. The time variation of the steering current manifests as a waveform, i.e., a signal with frequency. The extraction band refers to the frequency band of the steering current signal that is extracted as road surface information. The extraction of the signal in the extraction band can be achieved, for example, using a bandpass filter.

[0037] The filter gain is the gain calculated by multiplying the signal in the extracted frequency band. The larger the filter gain, the greater the degree to which the road surface information reflects the operational reaction force. That is, the larger the filter gain, the greater the amount of road surface information transmitted to the operating component 20. The controller 4 sets the operational reaction force based on the signal after multiplying the extracted frequency band signal by the filter gain and transmits the road surface information to the operating component 20.

[0038] In Sport mode, compared to Normal mode, a wider extraction frequency band is set to reflect more road surface information in the operating reaction force, and a larger filter gain is set to transmit more road surface information to the operating component 20. In Comfort mode, compared to Normal mode, a narrower extraction frequency band is set to reflect less road surface information in the operating reaction force, and a smaller filter gain is set to transmit less road surface information to the operating component 20. During the transmission change control, controller 4 gradually shifts the extraction frequency band and filter gain towards the settings of the switched control mode.

[0039] (Reaction force change control)

[0040] Reaction force variation control is a control that gradually changes the control constant related to the amount of operational reaction force applied to the operating quantity of the operating component 20. Reaction force variation control is a control that gradually changes a predetermined control constant related to the control of the reaction force application device 25 in a manner consistent with the switched control mode. Reaction force variation control can also be called operation feel variation control.

[0041] In reaction force change control, the control constant of the changed object is the gain, or auxiliary gain, used in the calculation of the operating reaction force. The larger the auxiliary gain, the smaller the operating reaction force. The auxiliary gain can also be described as the degree to which the operating reaction force is reduced. In reaction force change control, the auxiliary gain in the operating reaction force varies according to the control mode. In motion mode, a smaller auxiliary gain is set compared to normal mode, for example, to create a heavier operating feel. In comfort mode, a larger auxiliary gain is set compared to normal mode, for example, to create a lighter operating feel. Controller 4 gradually changes the control constant of the changed object, i.e., the auxiliary gain, towards the setpoint of the switched control mode in reaction force change control.

[0042] (Transmission ratio change control)

[0043] The transmission ratio change control is a control that gradually changes the control constant related to the ratio of the steering angle of wheels 11 and 12 to the operating amount of operating component 20, i.e., the transmission ratio. The transmission ratio change control gradually changes the prescribed control constant related to the control of steering unit 3 in a manner consistent with the switched control mode.

[0044] The gear ratio is set, for example, by a mapping table that outputs the corresponding gear ratio when the vehicle speed and the operation amount of the operating component 20 are input. The control constant in gear ratio change control can also be called the gear ratio (output value) in the mapping table. Gear ratio change control can also be called control that gradually changes the mapping table. A situation where the steering angle increases relative to the same operation means that the steering response is faster relative to the operation, that is, the handling feel becomes more agile. Conversely, a situation where the steering angle decreases relative to the same operation means that the steering response is slower relative to the operation, that is, the handling feel is sluggish.

[0045] In Sport mode, a larger gear ratio is set compared to Normal mode, for example, to provide a more agile feel. In Comfort mode, a smaller gear ratio is set compared to Normal mode, for example, to provide a more sluggish feel. Controller 4 gradually changes the gear ratio towards the set value of the switched control mode during gear ratio change control.

[0046] (An example of switching control modes)

[0047] In this example, if a control mode switching operation is performed, transmission change control is executed regardless of whether the vehicle state meets the specified conditions. On the other hand, if a control mode switching operation is performed, reaction force change control and transmission ratio change control are executed after determining that the vehicle state meets the specified conditions. The specified conditions include a first specified condition set for reaction force change control and a second specified condition set for transmission ratio change control.

[0048] like Figure 2 As shown, when the driver's operation instructs a switch from the normal control mode to the sport mode, the transmission change control is executed first. The impact on vehicle stability is minimal, so transmission change control is executed regardless of the vehicle's state. Therefore, if a control mode switch is indicated at time t1, transmission change control immediately begins, the extracted bandwidth gradually widens, and the filter gain gradually increases.

[0049] The value of the control constant corresponding to the control mode is called the "set value". For example, the set value of the control constant corresponding to the normal mode is called the normal set value F. n 、Gf n Ga n R n The set value of the control constant corresponding to the motion mode is called the motion set value F. s 、Gf s Ga s R s The set value of the control constant corresponding to the comfort mode is called the comfort set value F. c 、Gf c Ga c R c By changing each control constant from its normal setpoint to its motion setpoint, the control mode is completely switched from normal mode to motion mode.

[0050] In this example, the transfer change control sets the control constant with a temporary overshoot relative to the control mode setpoint after the switch. The overshoot is set to a predetermined amount. In the transfer change control, controller 4 makes the decimation band ratio equal to the motion setpoint F. s Wide, making the filter gain ratio greater than the motion setpoint Gf s Larger. This allows the driver to perceive the control mode switch more strongly and intuitively for a temporary period. Controller 4 maintains each control constant at the overshoot value for a specified period or until certain conditions are met. Controller 4, for example, gradually transitions from the overshoot value to the motion setpoint F in a manner synchronized with the completion of other characteristic change controls. s 、Gf s Therefore, the target value can ultimately be achieved.

[0051] After determining that the vehicle state meets the first specified condition, reaction force change control is executed. The reaction force change control is also the same as described above, relative to the switched control mode setting value Ga. s The control constant is set using a temporary overshoot method. After determining that the vehicle state meets the second specified condition, transmission ratio change control is executed. The second specified condition is set to require higher vehicle stability than the first specified condition. For example, vehicle stability is higher at lower speeds. Furthermore, when the steering angle is set to 0 degrees when the vehicle is moving forward, the smaller the steering angle, the higher the vehicle stability; that is, the stability is higher in the forward state compared to the turning state. For example, if vehicle stability is expressed numerically as a stability factor, then for that value, the lower the speed and the smaller the steering angle, the higher the stability. Moreover, in this description, vehicle stability is based on the premise that the vehicle is moving forward.

[0052] The first predicate condition is set, for example, as "when the vehicle is moving forward, the speed is below the specified high speed" and "when the vehicle is turning, the speed is below the specified low speed, and the steering angle is below the specified angle" (specified high speed > stable speed > specified low speed). The second predicate condition is set, for example, as "the vehicle is not turning, and the speed is below the stable speed." Furthermore, conditions for the vehicle not being in a specific state are added to each predicate condition. Examples of specific states include the vehicle reversing, wheel slippage, or rapid deceleration.

[0053] according to Figure 2 For example, at time t1, when a control mode switching indication is present, the vehicle is turning in the stable speed range, and its stability is relatively low. At this time, no vehicle state determination is made, but change control is initiated, and a comparison between the vehicle state and specified conditions is performed. Then, the vehicle's steering angle gradually decreases, and at time t2, the first specified condition is met, and reaction force change control is executed. Then, at time t3, the vehicle reaches a stable speed, for example, 50 km / h, and the second specified condition is met, and gear ratio change control is executed.

[0054] At time t3, if the transmission ratio change control begins, the gradual change of the transmission ratio is synchronized with it, and the gradual change of the set value begins to eliminate the overshoot of the transmission ratio change control and the reaction force change control. Controller 4 synchronizes the gradual change period of the reaction force change control after overshoot with the gradual change period of the transmission ratio change control (times t3 to t4). That is, controller 4 synchronizes the completion of the transmission ratio change control with the completion of the reaction force change control. Thus, by gradually changing the transmission ratio, the imbalance between the transmission ratio and the operating reaction force is suppressed. At time t4, the control mode is completely switched from the normal mode to the motion mode. The period from time t1 to t4 can be called the control mode switching period. In this example, the transmission ratio change control begins, then the reaction force change control begins, then the transmission ratio change control begins, and then, at the same time, all characteristic change controls end.

[0055] like Figure 3 As shown, if controller 4 receives a control mode switching instruction (S1), it immediately executes transmission change control (S2) and simultaneously determines whether specific characteristic change control can be executed. Controller 4, as a timing coordinator, determines whether the execution of reaction force change control is permitted (S3). That is, controller 4 determines whether the vehicle state meets the first specified condition. Simultaneously, controller 4, as a timing coordinator, determines whether the execution of transmission ratio change control is permitted (S4). That is, controller 4 determines whether the vehicle state meets the second specified condition.

[0056] When the vehicle state meets the first specified condition (S3: Yes), controller 4 starts reaction force change control (S5). When the vehicle state meets the second specified condition (S4: Yes), controller 4 starts transmission ratio change control (S6). When receiving the switching instruction, both reaction force change control and transmission ratio change control can be started simultaneously when the vehicle state meets the second specified condition.

[0057] Controller 4 synchronizes the completion times of multiple characteristic change controls (S7, S8, S9). Multiple characteristic change controls are executed in a coordinated manner. Furthermore, the completion times of each characteristic change control can be adjusted sequentially within a range that does not compromise vehicle stability. Additionally, the completion of the change control can be transmitted without synchronization with other characteristic change controls. In all characteristic change controls, if the control constant becomes the setpoint of the switched control mode, the control mode switch is complete (S10). Thus, by executing a control constant that does not impede vehicle stability immediately after the switch indication, the mode change can be easily transmitted to the driver.

[0058] (other)

[0059] This invention is not limited to the embodiments described above. For example, the reaction force change control can be performed in the same way as the transmission change control, without determining the vehicle state. Furthermore, the characteristic change control can also be related to steering characteristics, changing characteristics (functions) other than those described above. The controller 4 can also be set to control modes other than those described above. In addition to the above, the technology of this invention can be implemented in various forms with various modifications and improvements based on the knowledge of those skilled in the art.

Claims

1. A steering system, which is an electric steering system, characterized in that, have: The operating unit includes operating components for steering operations performed by a driver and a reaction force applying device for applying an operating reaction force to the operating components. The steering unit is mechanically separated from the aforementioned operating unit and steers the wheels according to the supplied steering current. as well as The controller controls the steering unit and the reaction force application device based on operation signals received from the operation unit related to the operation of the operation components, and steering angle signals received from the steering unit related to the actual steering angle of the wheels. The aforementioned controller is equipped with multiple control modes, each implementing different steering characteristics. The controller described above is configured to change the steering characteristics by executing various characteristic-changing controls that alter predetermined control constants related to the control of the reaction force application device and / or the steering unit, based on the switching of the control mode described above. The controller is configured to, based on the switching of the control mode, execute one or more of the aforementioned characteristic change controls after determining that the vehicle state meets the specified conditions, and execute one or more other aforementioned characteristic change controls regardless of whether the vehicle state meets the specified conditions.

2. The steering system according to claim 1, characterized in that, In the aforementioned controller, as the aforementioned characteristic change control, there are transmission change controls that gradually change the control constant related to the amount of road information transmitted to the aforementioned operating component, and transmission ratio change controls that gradually change the control constant related to the ratio of the steering angle of the wheel to the operating amount of the aforementioned operating component, i.e., the transmission ratio. The above controller is configured as follows After determining that the vehicle condition meets the aforementioned conditions, the aforementioned transmission ratio change control is executed. Regardless of whether the vehicle status meets the above-mentioned conditions, the above-mentioned transfer change control shall be executed.

3. The steering system according to claim 2, characterized in that, In the aforementioned controller, as the aforementioned characteristic change control, a reaction force change control is provided that gradually changes the control constant related to the amount of the applied reaction force for the operation quantity of the aforementioned operating component. The controller synchronizes the completion of the transmission ratio change control with the completion of the reaction force change control.

4. The steering system according to claim 3, characterized in that, The aforementioned conditions include: a first condition set relative to the aforementioned reaction force change control, and a second condition that requires higher vehicle stability than the first condition, i.e., a condition set relative to the aforementioned transmission ratio change control. The controller is configured to execute the reaction force change control after determining that the vehicle state meets the first specified condition. After determining that the vehicle status meets the second specified condition, the transmission ratio change control is executed.

5. The steering system according to claim 3 or 4, characterized in that, When the value of the control constant corresponding to the above control mode is set to the set value... In the aforementioned transmission change control and / or reaction force change control, the aforementioned controller gradually changes the aforementioned control constant by temporarily overshooting the aforementioned control constant relative to the aforementioned set value of the switched control mode.

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