Steering system

Abstract

We provide a highly practical steer-by-wire steering system. [Solution] In a steer-by-wire steering system comprising an operating member 10 operated by a driver, a reaction force applying device 12 that applies an operating reaction force Tc to the operating member, a steering device 16 that steers the wheels using a steering motor 38 which is an electric motor as a drive source, and controllers 40, 42 that control the reaction force applying device and the steering device, the controller is configured to determine an operating reaction force including a steering current-dependent component Tcb which is a component based on the current Is supplied to the steering motor, and a steering speed-dependent correction component Tcd which reduces the steering current-dependent component based on the steering speed ω', and to determine the steering speed-dependent correction component so that it does not become larger than the value at the set speed when the steering speed exceeds the set speed (130).

Description

Technical Field

[0001] The present invention relates to a steer-by-wire type steering system mounted on a vehicle.

Background Art

[0002] A steer-by-wire type steering system (hereinafter sometimes referred to as a "steer-by-wire system") does not mechanically connect an operation member such as a steering wheel to a steered wheel. Therefore, the steer-by-wire system is provided with a reaction force applying device for applying an operation reaction force to the operation member. The operation reaction force is generally desirably set to a magnitude corresponding to the load of the steering device, that is, the steering force for steering the wheel, and may be determined based on the estimated steering force. Basically, when the steering device has a steering motor that is an electric motor as a drive source, a current corresponding to the steering force is supplied to the steering motor, so the steering force can be estimated based on that current. Therefore, the operation reaction force may be determined based on the steering force estimated based on the supply current. However, since a damping force due to mechanical friction or the like occurs in the steering device, for example, in the steer-by-wire system described in the following patent document, correction based on the steering speed is performed on the steering force estimated based on the current supplied to the steering motor.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Due to the characteristics of electric motors, there is an upper limit to the supplied current, and even if steering of the wheels at high speeds is required, it is not always possible to supply a current corresponding to that speed. On the other hand, in the steer-by-wire system described in the above-mentioned patent document, for example, the correction based on the damping force is simply performed so that the estimated steering force decreases as the steering speed increases. Therefore, in the above-mentioned steer-by-wire system, when the steering speed becomes high enough, a difference arises between the actual steering force and the estimated steering force, and the operating reaction force is not appropriate. In other words, it gives the driver a sense of discomfort when steering. As can be seen from this, there is still much room for improvement in determining the operating reaction force of a steer-by-wire system, and the practicality of the steer-by-wire system can be improved by making some improvements. The present invention has been made in view of such circumstances, and aims to provide a highly practical steer-by-wire type steering system. [Means for solving the problem]

[0005] To solve the above problems, the steering system of the present invention is A steer-by-wire steering system comprising an operating member operated by the driver, a reaction force applying device that applies an operating reaction force to the operating member, a steering device that steers the wheels using a steering motor which is an electric motor as a drive source, and a controller that controls the reaction force applying device and the steering device, The controller determines the operating reaction force which includes a steering current-dependent component, which is a component based on the current supplied to the steering motor, and a steering speed-dependent correction component for reducing the steering current-dependent component based on the steering speed, and is configured to determine the steering speed-dependent correction component such that it does not become larger than the value at the set speed when the steering speed exceeds the set speed. [Effects of the Invention]

[0006] According to the steer-by-wire system of the present invention, since an upper limit is set for the steering speed-dependent correction component, even when the steering speed exceeds a certain level, the component of the operating reaction force that serves as an indicator of the steering force, i.e., the steering force-dependent component, does not become too small. As a result, even when the steering speed exceeds a certain level, an appropriate operating reaction force is suitably maintained, and the driver is less likely to experience any discomfort in steering. As will be explained in detail later, setting an upper limit for the steering speed-dependent correction component is particularly effective, for example, during rapid steering operations to correct wheel slippage on low-friction surfaces. Embodiments of the Invention

[0007] As explained earlier, the "steering current-dependent component" in this invention is the main component that indicates the steering force, which is the force generated by the steering device to steer the wheels. When the steering device is configured to steer the left and right wheels by moving a steering rod (rack bar) that connects the left and right wheels from side to side, the steering force can be considered as the axial force acting on the steering rod, that is, the so-called axial force. As explained earlier, the "steering speed-dependent correction component" can be considered as a component that indicates the damping force caused by the mechanical structure of the steering device. It is a component that compensates for the component that increases with increasing steering speed, that is, a component that greatly reduces the steering current-dependent component. Incidentally, "steering speed" is generally the rate of change in the steering angle (toe angle) of the wheel being steered, but if there is a relationship between the rotational speed of the steering motor and the steering angle of the wheel such that they form a predetermined gear ratio, it can also be considered as the rotational speed of the steering motor, or as the operating speed of the components of the steering device such as the steering rod.

[0008] The "set speed" should be set to a value such that, if exceeded, the steering speed can be considered to have exceeded the speed in normal steering operations. In short, it should be set to a value such that excessive steering operations can be presumed to be occurring. From another perspective related to the NT characteristics (rotational speed-torque characteristics) of the steering motor, which is an electric motor, the set speed should be set to a speed such that the torque that the steering motor can generate according to its NT characteristics is between 40% and 60% of its maximum torque. If such an upper limit is set, the steering speed-dependent correction component should be determined such that, for example, it increases as the steering speed increases when the steering speed is below the set speed (e.g., linearly).

[0009] In the steer-by-wire system of the present invention, the operating reaction force may be determined by further including a steering acceleration-dependent correction component to reduce the steering current-dependent component based on the steering acceleration. This "steering acceleration-dependent correction component" can be considered a component that indicates the inertia of the steering device's operation. In situations such as the return of the steering member, the steering acceleration changes relatively large. As will be explained in detail later, the steering acceleration-dependent correction component is a component that compensates for the deviation of the operating reaction force, and by including this component, a good feel of operation can be maintained in such situations. However, if the steering acceleration is too high, this component may also cause the operating reaction force, more specifically the steering force-dependent component which is one of its components, to lag behind, potentially causing an unnatural feeling in the steering operation. When adopting this steering acceleration-dependent correction component, it is desirable that the component not become larger than its value at the set acceleration when the steering acceleration exceeds the set acceleration.

[0010] The "set acceleration" should be set to a value such that, if it is exceeded, the steering acceleration can be considered to have exceeded the acceleration in normal steering operations. In other words, it should be set to a value such that it can be presumed that emergency steering operations are being performed. Specifically, the set acceleration should be set to the value obtained when the steering member is operated (reciprocating) at the above set speed for steering speed between 1.5 Hz and 2.5 Hz. When such an upper limit is set, the steering acceleration-dependent correction component should be determined such that, for example, it increases as the steering acceleration increases when the steering acceleration is below the set acceleration (e.g., linearly). [Brief explanation of the drawing]

[0011] [Figure 1] This figure shows the overall configuration of the steering system in the embodiment. [Figure 2] This is a functional block diagram of the controller for the steering system in the embodiment. [Figure 3] This graph illustrates the steering speed-dependent and steering acceleration-dependent components of the steering reaction force. [Modes for carrying out the invention]

[0012] Hereinafter, as an embodiment for carrying out the present invention, a steer-by-wire type steering system, which is an embodiment of the present invention, will be described in detail with reference to the drawings. In addition to the embodiments described below, the present invention can be carried out in various forms by making various changes and improvements based on the knowledge of those skilled in the art, starting with the forms described in the section on "Embodiments of the Invention" above. [Examples]

[0013] [1] Overall configuration of the steering system The steering system of this embodiment (hereinafter sometimes referred to as "this steering system" or "this system") is a steer-by-wire type steering system that can steer the wheels without the driver's operating force applied to an operating member. As shown in Figure 1, it is composed of an operating member, a steering wheel 10, a reaction force actuator 12 which is a reaction force applying device to which the steering wheel 10 is connected, and a steering actuator 16 which is a steering device that connects two left and right wheels 14, each of which is a steering wheel, and steers them together. Incidentally, the steering wheel 10 is rotated by the driver, and the reaction force actuator 12 is configured to receive this operation and to apply a reaction force (hereinafter sometimes referred to as "operating reaction force") to the steering wheel 10, more specifically to the operation of the steering wheel 10.

[0014] The reaction force actuator 12 comprises a steering column 20 supported by the reinforcement of the instrument panel, a steering shaft 22 rotatably held in the steering column 20, and a reaction force motor 24, which is an electric motor for applying rotational torque to the steering shaft 22 via a power transmission mechanism. The steering wheel 10 is attached to the rear end of the steering shaft 22. The power transmission mechanism, although a detailed structural description is omitted, comprises a worm attached to the motor shaft of the reaction force motor 24 and a worm wheel attached to the steering shaft 22 that meshes with the worm. The reaction force motor 24 is a three-phase brushless DC motor and functions as the drive source for the reaction force actuator 12. The torque generated by the reaction force motor 24 applies a reaction force torque as an operating reaction force to the steering wheel 10 connected to the steering shaft 22.

[0015] The steering actuator 16 comprises a generally cylindrical housing 30 supported by the chassis in an orientation extending to the left and right, a steering rod (rack bar) 32 held in the housing 30 so as to be non-rotatable and movable from side to side, and a pair of tie rods 34 connected to the left and right ends of the steering rod 32 via ball joints. The ends of each tie rod 34 are connected to the wheels 14 via ball joints. More specifically, each tie rod 34 is connected via ball joints to the knuckle arm of a steering knuckle, which is held rotatably on the suspension arm and holds the wheel 14 so as to be rotatable.

[0016] The steering rod 32 has a screw groove 36 formed therein. Although not shown in the illustration, a nut that holds bearing balls and screws into the screw groove 36 is held inside the housing 30 so as to be immovable from side to side but rotatable. In other words, the steering rod 32 and the nut constitute a ball screw mechanism. An electric motor, the steering motor 38, is attached to the housing 30, and the steering motor 38 rotates the nut via a power transmission mechanism. Incidentally, although not shown in the illustration, the power transmission mechanism includes a pulley attached to the motor shaft of the steering motor 38 and a timing belt wrapped around the pulley and the outer circumference of the nut. The steering motor 38 is a three-phase brushless DC motor and functions as a drive source for the steering actuator 16. By rotating the steering motor 38, the steering rod 32 is moved from side to side, and the left and right wheels 14 are steered together.

[0017] The control of the reaction force actuator 12 is performed by a reaction force electronic control unit (hereinafter sometimes referred to as "reaction force ECU") 40 attached to the reaction force motor 24. The reaction force ECU 40 is composed of a computer including a CPU, ROM, RAM, etc., and an inverter which is a driver (drive circuit) of the reaction force motor 24, and is powered by a battery. Similarly, the control of the steering actuator 16 is performed by a steering electronic control unit (hereinafter sometimes referred to as "steering ECU") 42 attached to the steering motor 38. The steering ECU 42 is composed of a computer including a CPU, ROM, RAM, etc., and an inverter which is a driver (drive circuit) of the steering motor 38, and is powered by a battery.

[0018] The reaction force ECU 40 and the steering ECU 42 cooperate with each other, and they constitute one controller of the steering system. Therefore, the reaction force ECU 40 and the steering ECU 42 are connected by a dedicated high-speed communication line 44. Incidentally, they are both also connected to a CAN (car area network or controllable area network) 46 provided in the vehicle. A vehicle speed sensor 48 for detecting the vehicle speed v which is the running speed of the vehicle is also connected to this CAN 46.

[0019] Regarding control, although the detailed structure description of the reaction force actuator 12 is omitted, it has an operation torque sensor 50 for detecting an operation torque To as an operation force applied by the driver to the steering wheel 10 by detecting the torsional amount of the steering shaft 22. It also has an operation angle sensor 52 for detecting the operation angle δ of the steering wheel 10 by detecting the rotation angle of the steering shaft 22, and a reaction force motor rotation angle sensor 54 for detecting the rotation angle (rotation phase) θmc of the reaction force motor 24 for the purpose of switching the energized phase, etc.

[0020] Regarding the steering actuator 16, since there is a specific relationship between the steering angle of the wheel 14 and the lateral movement position of the steering rod 32, it has a steering angle sensor 56 that detects the movement position of the steering rod 32 in order to detect the steering angle of the wheel 14. Briefly, a rack 58 is formed on the steering rod 32, and a pinion shaft 60 that meshes with the rack 58 is held in the housing 30. The steering angle can also be the toe angle of the wheel 14, but in this system, the rotation angle of the pinion shaft 60 detected by the steering angle sensor 56 is treated as the steering angle ω of the wheel 14. The steering actuator 16 also has a steering motor rotation angle sensor 62 for detecting the rotation angle (rotation phase) θms of the steering motor 38 for purposes such as switching the energized phase.

[0021] [2] Controller functions The controller of this steering system, which consists of a reaction force ECU 40 and a steering ECU 42, has the functional configuration shown in the functional block diagram in Figure 2. This functional configuration is realized by a computer executing a predetermined program. The inputs to or outputs from each component (functional unit) shown in the figure are mostly signals indicating values ​​such as torque, its components, steering angle, and operating angle. However, to avoid redundancy in the explanation, in the following explanation, we will simply say that torque, its components, steering angle, and operating angle are input to or output from each component. Furthermore, for ease of understanding, the functions related to steering control by the steering ECU 42 will be explained first, followed by the functions related to reaction force control by the reaction force ECU 40.

[0022] (a) Steering control Steering control is the control of the steering angle ω of the wheel 14 that is steered by the steering actuator 16, and the steering ECU 42, which acts as the steering control unit, has a target steering angle determination unit 100, a steering torque determination unit 102, and a steering energization control unit 104.

[0023] In the control of this steering system, the steering angle ω is used as the amount of steering of the wheel 14. However, this steering angle ω is not the value detected by the steering angle sensor 56, but rather a value converted based on the steering motor rotation angle θms detected by the steering motor rotation angle sensor 62. Therefore, the steering ECU 42 has a steering angle conversion unit 106 that converts the steering motor rotation angle θms detected by the steering motor rotation angle sensor 62 into a steering angle ω. Since the cumulative amount of the steering angle ω and the steering motor rotation angle θms has a relationship according to a predetermined reduction ratio, the steering angle conversion unit 106 performs the conversion based on that reduction ratio.

[0024] The target steering angle determination unit 100 determines the target steering angle ω, which is the control target for the steering angle ω, based on the operating angle δ converted by the operating angle conversion unit 108 of the reaction force ECU 40, which will be described later. * The steering system determines the steering gear ratio γ, that is, the ratio of the steering angle ω to the operating angle δ, according to the vehicle speed v. The target steering angle determination unit 100 determines the target steering angle ω by referring to the stored map data based on the operating angle δ and the vehicle speed v. * This will be determined. Incidentally, the method for changing the steering gear ratio γ is a common one, so we will omit the explanation here.

[0025] The steering torque determination unit 102 is a functional unit that determines the steering torque Ts required to steer the wheel 14. The steering torque Ts can be thought of as, for example, the torque that the steering motor 38 should generate. Specifically, it is calculated by comparing the current actual steering angle ω converted by the steering angle conversion unit 106 with the target steering angle ω * Based on this, the target steering angle ω * The steering angle deviation Δω, which is the deviation of the steering angle ω relative to the given value, is determined, and the steering torque Ts to be generated is determined according to the PID feedback control law based on this steering angle deviation Δω. This method of following the feedback control law is common and will not be explained here.

[0026] The steering power supply control unit 104 includes an inverter, which is the drive circuit (driver) for the steering motor 38. Based on the determined steering torque Ts, the steering power supply control unit 104 determines the steering current Is, which is the current to be supplied to the steering motor 38, and supplies this steering current Is from the inverter to the steering motor 38. The steering ECU 42 has a current sensor 110 for detecting the steering current Is that is actually being supplied.

[0027] (b) Control of reaction force The reaction force control unit, the reaction force ECU 40, controls the reaction force torque Tc to be applied to the steering wheel 10 by the reaction force actuator 12, which is a reaction force application device. The reaction force ECU 40 has an assist component determination unit 112 and a steering force dependent component determination unit 114, which determine the assist component Tca and the steering force dependent component Tcs, respectively, which are components of the reaction force torque Tc. The steering force-dependent component Tcs includes the steering current-dependent component Tcb, which is the basic component; the steering speed-dependent correction component (damping compensation component) Tcd, which corrects the steering current-dependent component Tcb by using the damping force due to the structure of the steering actuator 16 as an indicator; and the steering acceleration-dependent correction component (inertia compensation component) Tci, which corrects the steering current-dependent component Tcb by using the inertial force related to the operation of the steering actuator 16 as an indicator. The system has a steering current-dependent component determination unit 116, a steering speed-dependent correction component determination unit 118, and a steering acceleration-dependent correction component determination unit 120, which determine these components Tcb, Tcd, and Tci, respectively.

[0028] In the control of this steering system, the steering angle δ is used as the amount of steering of the steering wheel 10. Therefore, similar to the steering ECU 42, the reaction force ECU 40 has a steering angle conversion unit 108 that converts the reaction force motor rotation angle θmc detected by the reaction force motor rotation angle sensor 54 into a steering angle δ. Since the integrated amount of the steering angle δ and the reaction force motor rotation angle θmc has a relationship according to a predetermined reduction ratio, the steering angle conversion unit 108 performs the conversion based on that reduction ratio.

[0029] To explain the determination of each component of the reaction torque Tc described above, the assist component Tca is similar to the assist force in so-called power steering, and the assist component determination unit 112 determines the assist component Tca based on the operating torque To and vehicle speed v detected by the operating torque sensor 50. Simply put, the assist component Tca is determined to be a larger value the larger the operating torque To is, and when the vehicle speed v is high, it is determined to be a smaller value in order to make the operating feel that the driver receives in response to the operation of the steering wheel 10 heavier, and when the vehicle speed v is low, it is determined to be a larger value in order to make the operating feel lighter. The direction of the assist component Tca is the same as the direction of operation of the steering wheel 10, that is, the direction of steering operation.

[0030] The steering force-dependent component Tcs can be considered a central component of the reaction torque Tc, and broadly speaking, it is a component that allows the driver to feel the steering force, which is the force required to steer the wheel 14. It can also be considered a component based on the force (axial force) acting on the steering rod 32 of the steering actuator 16 in its axial direction, or in other words, it is a component that allows the driver to feel, for example, the force acting on the wheel 14 from the road surface. The steering force-dependent component Tcs is generally a component in the direction opposite to the steering operation direction.

[0031] The steering current-dependent component Tcb is the fundamental component, or in other words, the principal component, of the steering force-dependent component Tcs. The steering current-dependent component determination unit 116 determines the steering current-dependent component Tcb by multiplying the actual steering current Is detected by the current sensor 100 by the set current-dependent gain Kb. In the reaction force ECU 40, the steering speed ω' (=dω / dt) is calculated by the differentiator 122 based on the steering angle ω converted by the steering angle conversion unit 106, and this steering speed ω' is output via the low-pass filter 124. Also, based on the steering angle ω, the steering acceleration ω'' (=d 2 ω / dt 2The steering acceleration ω'' is calculated and output via a low-pass filter 128. The steering speed-dependent correction component determination unit 118 has a limiting processor 130 and a gain multiplier 132, and determines the steering speed-dependent correction component Tcd by multiplying the steering speed ω'' output via the limiting processor 130 by the damping compensation gain Kd. Similarly, the steering acceleration-dependent correction component determination unit 120 has a limiting processor 134 and a gain multiplier 136, and determines the steering acceleration-dependent correction component Tci by multiplying the steering acceleration ω'' output via the limiting processor 134 by the inertia compensation gain Ki. The processing in the limiting processors 130 and 134 will be explained in detail later.

[0032] The steering current-dependent component Tcb is corrected by the subtractor 138 based on the steering speed-dependent correction component Tcd and the steering acceleration-dependent correction component Tci, and as a result, the steering force-dependent component Tcs is determined. The steering force-dependent component Tcs and the assist component Tca are added by the adder 140 to determine the reaction force torque Tc.

[0033] The determined reaction torque Tc is input to the reaction force energization control unit 142. The reaction force energization control unit 142 includes an inverter, which is the drive circuit (driver) for the reaction force motor 24. Based on the reaction force torque Tc, the reaction force energization control unit 142 determines the reaction force current Ic, which is the current to be supplied to the reaction force motor 24, and supplies that reaction force current Ic from the inverter to the reaction force motor 24.

[0034] [3] Steering speed-dependent correction component, steering acceleration-dependent correction component As mentioned above, the steering speed-dependent correction component Tcd in reaction force control can be considered a component that indicates the damping force caused by friction, etc., of the steering actuator 16, and is set to increase as the steering speed ω' increases. However, when the steering speed ω' becomes high enough, the steering speed-dependent correction component Tcd becomes too large, causing the reaction force torque Tc, which is the operating reaction force, to be inappropriate, resulting in an unnatural feeling in the driver's steering operation. For this reason, this system imposes a limit on the steering speed-dependent correction component Tcd.

[0035] To explain in more detail, the limiting processor 130 of the steering speed-dependent correction component determination unit 118 outputs an output steering speed ωout' for an input steering speed ωin', as shown in the graph in Figure 3(a). In other words, processing is performed so that the output steering speed ω' does not exceed the set speed ωth'. The set speed ωth' is set to a value that, if exceeded, can be considered as exceeding the speed in normal steering operations; in other words, a value that can be estimated as indicating excessive steering operation. With such an upper limit set for the steering speed ω', when the steering speed ω' is less than or equal to the set speed ωth', the steering speed-dependent correction component Tcd increases linearly as the steering speed ω' increases. However, when the steering speed ω' exceeds the set speed ωth', the steering speed-dependent correction component Tcd is maintained at the value when the steering speed ω' reaches the set speed ωth'.

[0036] Referring to the graph in Figure 3(b) which shows the NT characteristics (motor rotational speed-torque characteristics) of the steering motor 38, the set speed ωth' is set to a steering speed ω' that corresponds to the set motor rotational speed θms' (=dθms / dt) at which the output torque Tm of the steering motor 38 on the characteristic curve is 40% to 60% (specifically, 50%) of the maximum torque Tmmax.

[0037] On the other hand, as mentioned above, the steering acceleration-dependent correction component Tci in reaction force control can be considered a component that indicates the inertia of the operation of the steering actuator 16, and is set to increase as the steering acceleration ω'' increases. However, similar to the steering speed-dependent correction component Tcd, when the steering acceleration ω'' becomes high enough, the steering acceleration-dependent correction component Tci also becomes too large, resulting in an inappropriate reaction force torque Tc and causing discomfort to the driver's steering operation. Therefore, in this system, a limit is also imposed on the steering acceleration-dependent correction component Tci.

[0038] To explain in more detail, the limiting processor 134 of the steering acceleration-dependent correction component determination unit 120 outputs an output steering acceleration ωout" for an input steering acceleration ωin", as shown in the graph in Figure 3(c). In other words, processing is performed so that the steering acceleration ω" does not exceed the set acceleration ωth". The set acceleration ωth" is set to a value that, if exceeded, can be considered to have exceeded the acceleration in normal steering operations, or in other words, a value that can be presumed to indicate that emergency steering operations are being performed. With such an upper limit set for the steering acceleration ω", when the steering acceleration ω" is less than or equal to the set acceleration ωth", the steering acceleration-dependent correction component Tci increases linearly as the steering acceleration ω" increases, but when the steering acceleration ω" exceeds the set acceleration ωth", the steering acceleration-dependent correction component Tci is maintained at the value when the steering acceleration ω" becomes the set acceleration ωth.

[0039] More specifically, the set acceleration ωth'' is set to the value (for example, the maximum value) obtained when the handle 10 is operated back and forth at a speed of 1.5Hz to 2.5Hz (specifically, 2Hz) at the above set speed ωth''.

[0040] The steering speed-dependent correction component Tcd will be further explained with reference to the graph in Figure 3(d). The graph in Figure 3(d) schematically shows the change in the steering force-dependent component Tcs of the reaction torque Tc as the steering speed ω' increases with time t. As shown by the dashed line in the graph, the steering current-dependent component Tcb increases with increasing steering current Is. However, due to the characteristics of the steering motor 38, not all of the steering current Is becomes steering torque Ts, so the reaction torque Tc becomes excessive if only the steering current-dependent component Tcb is used. To compensate for this, the steering speed-dependent correction component Tcd is employed. However, if there is no limit on the steering speed-dependent correction component Tcd as explained above, that is, if the above upper limit is not set for the steering speed ω', then, as shown by the dashed line in the graph, when the steering speed ω' becomes high enough, the steering force-dependent component Tcs becomes too small. Therefore, by imposing the above-mentioned restrictions on the steering speed-dependent correction component Tcd, an appropriate steering force-dependent component Tcs can be obtained, as shown by the solid line in the graph. In other words, by limiting the steering speed-dependent correction component Tcd, an appropriate operating reaction force is applied to the steering wheel 10.

[0041] Next, we will further explain the steering acceleration-dependent correction component Tci, referring to the graph in Figure 3(e). The graph in Figure 3(e) schematically shows the change in the deviation (leading / delaying, so-called phase shift) of the steering force-dependent component Tcs of the reaction torque Tc due to a change in steering acceleration ω''. As shown by the dashed line in the graph, with only the steering current-dependent component Tcb, the steering force-dependent component Tcs is shifted toward the leading side, and this deviation becomes larger as the steering acceleration ω'' increases. To compensate for this, the steering acceleration-dependent correction component Tci is adopted. However, if there is no limit on the steering acceleration-dependent correction component Tci as explained earlier, that is, if the steering acceleration ω'' does not have the upper limit mentioned above, then, as shown by the dashed line in the graph, when the steering acceleration ω'' becomes high enough, the steering force-dependent component Tcs will actually lag, and this lag will increase as the steering acceleration ω'' increases. Therefore, by imposing the aforementioned limit on the steering acceleration-dependent correction component Tci, an appropriate steering force-dependent component Tcs can be obtained, as shown by the solid line in the graph. In other words, by limiting the steering acceleration-dependent correction component Tci, an appropriate operating reaction force will be applied to the steering wheel 10. [Explanation of symbols]

[0042] 10: Steering wheel (operating component) 12: Reaction actuator (reaction force application device) 14: Wheel 16: Steering actuator (steering device) 24: Reaction motor (drive source) 32: Steering rod 38: Steering motor (drive source) 40: Reaction ECU (controller) 42: Steering ECU (controller) 52: Operating angle sensor 54: Reaction motor rotation angle sensor 56: Steering angle sensor 62: Steering motor rotation angle sensor 110: Current sensor 112: Assist component determination unit 114: Steering force dependent component determination unit 116: Steering current dependent component determination unit 118: Steering speed dependent correction component determination unit 120: Steering acceleration dependent correction component determination unit 130: Limiting processor 134: Limiting processor

Claims

1. A steer-by-wire steering system comprising an operating member operated by the driver, a reaction force applying device that applies an operating reaction force to the operating member, a steering device that steers the wheels using a steering motor which is an electric motor as a drive source, and a controller that controls the reaction force applying device and the steering device, A steering system in which the controller determines the operating reaction force, which includes a steering current-dependent component that is based on the current supplied to the steering motor, and a steering speed-dependent correction component that reduces the steering current-dependent component based on the steering speed, and is configured to determine the steering speed-dependent correction component so that it does not become greater than the value at the set speed when the steering speed exceeds the set speed.

2. The steering system according to claim 1, wherein the set speed is set to a speed at which the torque that the steering motor can generate according to the N-T characteristics is 40% or more and 60% or less of the maximum torque.

3. The steering system according to claim 1, wherein the controller further determines an operating reaction force including a steering acceleration-dependent correction component for reducing the steering current-dependent component based on the steering acceleration, and determines the steering acceleration-dependent correction component such that it does not become larger than the value at the set acceleration when the steering acceleration exceeds the set acceleration.

4. The steering system according to claim 3, wherein the set acceleration is set to a value that can be estimated to indicate that steering operations are being performed in an emergency.

5. The steering system according to claim 3, wherein the set acceleration is set to the value obtained when the operating member is operated at the set speed at a frequency of 1.5 Hz or more and 2.5 Hz or less.

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