Steering control device and power steering system

Abstract

Steering control device (1) which controls a rotation angle of a motor (10) which drives a steering mechanism according to a rotation angle (θh) of a steering wheel (911), wherein the steering control device (1) comprises: a disturbance monitoring unit (23, 30) which calculates a steering reaction force torque generated by changing a steering angle (θh) by using the steering mechanism, and a steering angle control unit (21, 22) which has a target steering angle estimation unit (22) configured to estimate a target steering angle based on the steering reaction force torque and the rotation angle (θh) of the steering wheel (911), wherein the steering angle control unit (21, 22) reduces a difference between the target steering angle and a steering angle (θs) in the steering mechanism by driving the motor (10) according to the rotation angle (θh) of the steering wheel (911) and the steering reaction force torque as command values.

Description

Field of invention

[0001] The present invention relates to a steering control device and a power steering system. Background technology

[0002] Steering control devices that perform steering control on power steering systems are known. A conventional steering control is primarily an auxiliary control.

[0003] For example, JP 2003 - 200 844 A discloses a control device which calculates a current command value, which is a control target of a motor, based on a steering torque detected by a torque sensor, and which defines a steering reaction force based on a self-aligning torque estimated by a disturbance monitoring unit and feeds this back to the steering torque. State-of-the-art documents, patent documents

[0004] EP 3 210 853 A1 discloses an electric power steering system with a torque sensor for detecting a steering torque and a motor control unit for controlling a motor that exerts an assist torque on a steering system of a vehicle, comprising: a function for switching a control system of the motor between a torque control system for controlling a motor output torque and a position / speed control system for controlling a steering angle in accordance with a predetermined switching trigger.

[0005] Other power steering systems are known from EP 3 284 648 A1 and US 2007 / 0 169 984 A1. Overview of the invention; Problem to be solved by the invention

[0006] Control devices, as shown in JP 2003 - 200 844 A, are each provided with a torque feedback loop to achieve a high degree of control design freedom, system stability and processing of road surface information and disturbance information.

[0007] Unfortunately, torque feedback means that following a target torque is affected by torque loss and torque ripple in the motor. This necessitates complex compensation processing to suppress such influence. Furthermore, designing a compensator is not straightforward due to manufacturing variations and motor aging.

[0008] Therefore, one objective of the present invention is to implement a steering control system that is less affected by torque ripple. Means of solving the task

[0009] The problem is solved by a steering control device according to claim 1 and a power steering system according to claim 7. Exemplary further developments are set out in the dependent claims.

[0010] A steering control device according to an exemplary embodiment controls a rotation angle of a motor which drives a steering mechanism according to a rotation angle of a steering wheel, and comprises: a disturbance monitoring unit which calculates a steering reaction force torque generated by changing a steering angle by using the steering mechanism, and a steering angle control unit which reduces a difference between a target steering angle and a steering angle in the steering mechanism by driving the motor according to the rotation angle of the steering wheel and the steering reaction force torque as command values.

[0011] A power steering system according to an exemplary embodiment comprises: the steering control device described above, a motor which is controlled by the steering control device, and a power steering mechanism which is driven by the motor. Effects of the invention

[0012] The present invention makes it possible to implement a steering control system that is less affected by torque ripple. Brief description of the drawings Fig. Figure 1 is a schematic view representing a power steering system of an embodiment of the present invention. Fig. Figure 2 is a block diagram representing a configuration of an electric power steering system. Fig. Figure 3 is a representation that depicts a modification of a steering control device. Fig. Figure 4 is a representation that depicts a further modification of a steering control device. Fig. Figure 5 is a representation that depicts a modification of an electric power steering system. Embodiments for carrying out the invention

[0013] In the following, embodiments of a steering control device and a power steering system of the present disclosure are described in detail with reference to the accompanying drawings. To avoid unnecessarily redundant descriptions below and to facilitate understanding by those skilled in the art, unnecessarily detailed descriptions may be omitted. For example, a detailed description of already known items and a duplicate description of an essentially identical configuration may be omitted. Fig. Figure 1 is a schematic view representing a power steering system of an embodiment of the present invention.

[0014] As in Fig. Figure 1 illustrates a column-type electric power steering system in the present embodiment. An electric power steering system 9 is mounted on a steering mechanism of the wheels of a vehicle. The electric power steering system 9 is a column-type power steering system that directly reduces steering effort by utilizing power from a steering control device 1, which has an integrated motor. The electric power steering system 9 comprises: the steering control device 1, a steering shaft 914, and an axle 913.

[0015] The steering shaft 914 transmits an input torque, which is transmitted by a steering wheel 911, through a torsion bar 915 to the axle 913, which has wheels 912. In other words, the steering wheel 911 exerts a torque on the steering mechanism, which has wheels 912, axle 913 and steering shaft 914, via the torsion bar 915.

[0016] For example, power from the steering control device 1 is transmitted to the steering shaft 914 via gears. The column-type electric power steering system 9 uses a motor located in a motor compartment (not shown). Although the electric power steering system 9, which is in Fig. Figure 1, which is an example of the column type, shows that the power steering system of the present invention can be of the rack type.

[0017] A steering wheel angle θh, which is a rotation angle of the steering wheel 911, is detected by an angle sensor 916. The value detected by the angle sensor 916 is input to the steering control device 1 and used to calculate a target output for the steering control device 1. A torque transmitted from the torsion bar 915 to the steering shaft 914 is detected by a torque sensor 917. The value detected by the torque sensor 917 is also input to the steering control device 1 and used to calculate the target output for the steering control device 1.

[0018] A steering torque, which is transmitted from the steering wheel 911 through the torsion bar 915, and an auxiliary torque, which is generated by the power of the steering control device 1, are applied to the steering shaft 914 to generate a steering angle θs, which is a rotation angle of the steering shaft 914. Fig. Figure 2 is a block diagram representing a configuration of the electric power steering system 9. Fig. 2 is θh a steering wheel angle, θs a steering angle, K tor a torsion coefficient of the torsion bar 915 and STG(s) is a steering characteristic.

[0019] The torsion bar 915 is rotated due to a difference between the steering angle θh of the steering wheel 911 and the steering angle θs in order to generate a torque. The steering angle θh is detected by the angle sensor 916 and input to the steering control device 1. The torque generated in the torsion bar 915 is detected by the torque sensor 917 and input to the steering control device 1.

[0020] The steering control device 1 is equipped with a motor 10. The motor 10 is a so-called mechanical and electrical integrated motor and receives an input command value specifying a target output torque, and outputs the output torque. The steering control device 1 corresponds to an embodiment of a steering control device that controls the rotation angle of the motor 10, which drives the steering mechanism according to a rotation angle of the steering wheel 911.

[0021] The steering mechanism, which has the wheels 912 on the steering shaft 914 and exhibits the steering characteristic STG(s), is subjected to the torque generated in the torsion bar 915, the output torque of the motor 10, and a disturbance torque D(s). The steering angle θs is then generated by the sum of the aforementioned torques. The disturbance D(s) exerted on the steering mechanism is primarily a steering reaction force torque generated by changing the steering angle (a steering angle θs) using the steering mechanism, and a torque exerted on the wheels 912 due to unevenness in the road surface. This disturbance acts in a direction opposite to the steering force and the torque of the motor 10.The steering reaction force torque includes a self-aligning torque (SAT) and a torque associated with a frictional force between the wheels 912 and the ground. The steering control device 1 drives the motor 10 based on the steering wheel angle θh to approximate the steering angle θs to the steering wheel angle θh.

[0022] The steering control device 1 comprises: an angle feedback unit 21, a target steering angle estimation unit 22, a steering reaction force torque estimation unit 23, and a fault monitoring unit 30. The fault monitoring unit 30 comprises: an engine torque calculation unit 31, a steering torque estimation unit 32, and a filter 33.

[0023] The fault monitoring unit 30 receives: a drive current value Imotor of the motor 10, a detection value from the torque sensor 917 and the steering angle θs. Here, the steering angle θs is determined from a rotational speed of the motor 10, which is detected by a rotation sensor provided in the motor 10.

[0024] Motor 10 has a rotary shaft (output shaft) which is connected to steering shaft 914, for example, via a reduction gear. This means that motor 10 and steering shaft 914 always rotate together, regardless of whether motor 10 generates a torque to rotate steering shaft 914 or whether it is another torque. Consequently, the steering angle θs is calculated, for example, from the rotational speed of motor 10 based on a gear ratio.

[0025] The motor torque calculation unit 31 of the fault monitoring unit 30 inputs the drive current value Imotor of the motor 10 into the characteristics K of the motor 10 in order to calculate the output torque of the motor 10. The torque calculated by the motor torque calculation unit 31 is used for steering.

[0026] The steering torque estimation unit 32 of the fault monitoring unit 30 calculates a total amount of torque exerted on the steering system by inputting the steering angle θs into an inverse characteristic of the steering characteristic STG(s).

[0027] The calculated value of the engine torque calculation unit 31 is added to the detected value of the torque sensor 917, and the calculated value of the steering torque estimation unit 32 is further subtracted to obtain an estimated value of the disturbance D(s). This estimated value contains various disturbance components, so the disturbance monitoring unit 30 calculates the self-aligning torque (SAT) of the steering reaction force torque by filtering with the filter 33.

[0028] The self-aligning torque (SAT), which is calculated by the disturbance monitoring unit 30, is entered into the steering reaction force torque estimation unit 23 and is converted into a steering reaction force torque Tk, which is generated in the steering wheel 911, based on a special conversion characteristic.

[0029] A combination of the fault monitoring unit 30 and the steering reaction force-torque estimation unit 23, which is in Fig. Figure 2 shows an example of the fault monitoring unit referred to in the present invention. In the present embodiment, the steering reaction force torque Tk is calculated by using the detection value of the torque sensor 917, which corresponds to a measured value of the torque exerted on the steering mechanism by turning the steering wheel 911. This increases the calculation accuracy of the steering reaction force torque Tk.

[0030] The target steering angle estimation unit 22 estimates a target steering angle θs0 based on the steering reaction force torque Tk, which is obtained from the steering reaction force torque estimation unit 23, and the steering wheel angle θh, which is detected by the angle sensor 916. The target steering angle θs0 is estimated by the following expressions (1) and (2). Δθ×Ktor=Tk θs0=θh+Δθ

[0031] A difference between the target steering angle θs0, which is estimated as described above, and the steering angle θs is input into the angle feedback unit 21. A calculated torque increases with increasing difference. A command value specifying the torque, which is calculated as described above, is input into the motor 10 to generate an auxiliary torque.

[0032] The angular component Δθ, which is added to the steering wheel angle θh in the preceding expression (2), is added to maintain the current steering wheel angle θh against the steering reaction force torque Tk, so that the steering control device 1 ultimately performs an angular control to reduce any difference between the steering angle θs and the steering wheel angle θh. The target steering angle θs0 is determined by using the preceding expression (1), which contains the torsional coefficient K. tor of the torsion bar 915, estimated, so that the amount of a twist of the torsion bar 915 as a result of the angle control is suppressed.

[0033] A combination of the angle feedback unit 21 and the target steering angle estimation unit 22 corresponds to an example of a steering angle control unit which reduces a difference between the target steering angle θs0 and a steering angle (steering angle θs) in the steering mechanism by driving the motor 10 according to a rotation angle (steering wheel angle θh) of the steering wheel 911 and the steering reaction force torque Tk as command values.

[0034] As previously described, the steering control device 1 performs angle control, so that the influence of a cogging torque, which depends on the rotation angle of the motor 10, is less than that of torque control. Under angle control, compensation for torque ripple is simpler than under torque control. Consequently, the steering control in the steering control device 1 of the present embodiment is less affected by torque ripple. The electric power steering system 9 of the present embodiment then achieves smooth steering assistance. Modifications of the electric power steering system 9 and the steering control device 1 are described below. Fig. Figure 3 is a representation that depicts a modification of the steering control device 1.

[0035] Fig. Figure 3 represents the modification in which a speed control loop unit 24 is provided between the angle feedback unit 21 and the motor 10 of the steering control device 1. The speed control loop unit 24 calculates a loss torque, such as friction, which is generated depending on the speed of the motor 10, and performs a forward feedback control to input a compensation value to compensate for the loss torque of the motor 10.

[0036] The motor 10 outputs a total torque value consisting of a command value received from the angle feedback unit 21 and a compensation value received from the speed control loop unit 24. This achieves steering assistance by compensating for torque loss due to friction or similar factors. Fig. Figure 4 is a representation which shows a different modification of the steering control device 1.

[0037] Fig. Figure 4 represents the modification in which the fault monitoring unit 30 of the steering control device 1 is provided with a torque estimation unit 34. The torque estimation unit 34 estimates a torque exerted on the steering mechanism by a rotation of the steering wheel 911 by the torsion bar 915, based on the steering angle θs, which is calculated from a rotational speed of the motor 10, the steering wheel angle θh, which is detected by the angle sensor 916, and the torsion coefficient K. tor of the torsion bar 915. An estimation of the torque as described above makes the torque sensor unnecessary, thus simplifying a configuration around the steering mechanism.

[0038] Fig. Figure 5 is a representation that depicts a modification of the electric power steering system 9.

[0039] Fig. Figure 5 represents the modification, which is an electric power steering system 9 of a so-called "steer-by-wire" type, in which a steering wheel 911 and a steering shaft 914 are physically separated. That is, the steering wheel 911 is in a state in which a physical torque transmission path is disconnected from the steering mechanism. Consequently, no physical torque is transmitted from the steering wheel 911 to the steering mechanism.

[0040] A steering wheel angle θh of the steering wheel 911 is detected by an angle sensor 916 and is entered into a steering control device 1. Fig. Figure 5 represents the modification in which a steering torque is generated at the steering shaft 914 by the motor 10 in the steering control device 1. To enable a driver to have a feeling of steering wheel operation, a motor (not shown) generates a torque corresponding to a steering reaction force torque estimated by a steering reaction force torque estimation unit 23 and applies the torque to the steering wheel 911.

[0041] The steering control device 1, which is in the electric power steering system 9 of the modification, which is in Fig. The figure shown in section 5 is provided and preferably features a feedforward control system, which is located in Fig. Figure 4 illustrates this. Executing the forward coupling control described above allows the steering mechanism to respond naturally to an actuation of the steering wheel 911.

[0042] The previously described electric power steering system 9 of a "steer-by-wire" type does not have a torsion bar, so no torque, which is a control objective of torque control, is generated. Consequently, the previously mentioned angle control is more useful than torque control.

[0043] Although an example has been shown in the preceding description in which the steering control device 1 has a motor 10 built into it, the steering control device of the present invention can only have a control device without a motor built into it.

[0044] The embodiments and modifications described above are to be considered exemplary in every respect and not as limiting. The scope of the present invention is defined by the scope of the claims and not by the embodiments described above, and is intended to include all modifications within the meaning and scope equivalent to the scope of the claims. Description of reference symbols 1 Steering control device 9 electric power steering system 911 steering wheel 912 wheel 913 axle 914 Steering shaft 915 Torsion bar 916 Angle sensor 917 Torque sensor 10 Motor 21 Angle feedback unit 22 Target steering angle estimation unit 23 Steering reaction force-torque estimation unit 24 Speed ​​control loop unit 30 Fault monitoring unit 31 Motor torque calculation unit 32 Steering torque estimation unit 33 filters 34 Torque estimation unit

Claims

[1] Steering control device (1) which controls a rotation angle of a motor (10) which drives a steering mechanism according to a rotation angle (θh) of a steering wheel (911), wherein the steering control device (1) comprises: a disturbance monitoring unit (23, 30) which calculates a steering reaction force torque generated by changing a steering angle (θh) by using the steering mechanism, and a steering angle control unit (21, 22) which has a target steering angle estimation unit (22) configured to estimate a target steering angle based on the steering reaction force torque and the rotation angle (θh) of the steering wheel (911), wherein the steering angle control unit (21, 22) reduces a difference between the target steering angle and a steering angle (θs) in the steering mechanism by driving the motor (10) according to the rotation angle (θh) of the steering wheel (911) and the steering reaction force torque as command values. [2] Steering control device (1) according to claim 1, further comprising: a forward coupling control unit (24) which applies a forward coupling control to the motor (10) with a controlled variable which depends on a speed of the motor (10). [3] Steering control device (1) according to claim 1 or 2, wherein the steering wheel (911) exerts a torque on the steering mechanism through a torsion bar (915) and The target steering angle estimation unit (22) calculates the target steering angle by using a torsion coefficient of the torsion bar (915). [4] Steering control device (1) according to claim 3, wherein the fault monitoring unit (23, 30) calculates the steering reaction force torque by using a measured value of a torque exerted on the steering mechanism by a rotation of the steering wheel (911). [5] Steering control device (1) according to claim 3, wherein the fault monitoring unit (23, 30) calculates the steering reaction force torque by using an estimated value of a torque exerted on the steering mechanism by a rotation of the steering wheel (911). [6] Steering control device (1) according to claim 2, wherein the steering wheel (911) has a physical torque transmission path which is separate from the steering mechanism. [7] Power steering system (9) comprising: the steering control device (1) according to any one of claims 1 to 6, a motor (10) which is driven by a steering control device (1), and a power steering mechanism which is driven by the motor (10).

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