Control device and control method for electric steering system

Abstract

To provide a control device and a control method for an electrically-driven steering system that can effectively solve noise generation problems of a DC motor due to an unstable contact state of a brush and a commutator of the DC motor that a vehicle which is applied with the motor as a steering motor has.SOLUTION: There are disclosed a control device for an electrically-driven steering system and a method therefor, the control device including: a first sensor which detects a vehicle speed or wheel speed of a vehicle; a second sensor which detects a steering angle by operations of a steering wheel; and a control machine which selectively performs motor current control to determine a vehicle stop state from the vehicle speed detected by the first sensor or wheel speed information, and then reduce motor noise according to a motor applied current applied to a steering motor when determining a steering wheel fixed state from steering angle information detected by the second sensor.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a control device and a control method for an electric steering system, and more particularly, to a control device and a control method for an electric steering system that can effectively solve the problem of motor noise caused by an unstable contact state between the brushes and a commutator of a DC motor in a vehicle that uses a DC motor instead of a BLAC motor as a steering motor. [Background technology]

[0002] Generally, known power steering systems for increasing the steering force of a driver when steering an automobile include a hydraulic power steering (HPS) system that uses hydraulic pressure generated by a hydraulic pump to assist the driver's steering force, and a motor driven power steering system (MDPS, hereinafter referred to as "MDPS") that uses the output torque of an electric motor to assist the driver's steering force.

[0003] In particular, the MDPS system can control the output torque of the electric motor (steering motor) for steering assistance based on the vehicle's driving conditions, thereby providing improved steering performance and steering feel compared to hydraulic steering systems. As a result, MDPS systems that can change and control the steering assist force generated by the output of a motor according to driving conditions are widely used in vehicles that have been released recently.

[0004] The MDPS system is composed of a steering angle sensor that detects the steering angle (column input angle) caused by the driver's operation of the steering wheel, a torque sensor that detects the steering torque (steering wheel torque, column torque) input by the driver via the steering wheel, sensors such as a vehicle speed sensor, a wheel speed sensor, an acceleration sensor, an engine speed sensor, a yaw rate sensor, a controller (MDPS ECU), and a steering motor (MDPS motor).

[0005] In such a configuration, the controller obtains driver steering input information such as steering angle, steering angular velocity, and steering torque from sensor signals, as well as vehicle state information such as vehicle speed, wheel speed, acceleration, engine speed, and yaw rate, in order to control the operation and output of the steering motor.

[0006] Here, the steering angle represents the rotational position of the steering wheel, the steering angular velocity is the value of the steering wheel rotational speed obtained by, for example, differentiating the steering angle signal, and the steering torque is the torque applied to the steering wheel by the driver, i.e., the driver input torque for steering.

[0007] In addition, a torque sensor is a sensor for detecting the steering torque input by the driver via the steering wheel, and is widely known to detect this by utilizing the degree of twisting of a torsion bar, while an acceleration sensor is a sensor for detecting the acceleration of the vehicle in the forward, backward, left, and right directions to determine the vehicle's driving conditions.

[0008] In addition, the wheel speed sensor is a sensor for detecting the rotation speed of the vehicle wheels and judging the vehicle's driving conditions. Since the vehicle speed can be determined from the wheel rotation speed signal, the wheel speed sensor can also be used as a vehicle speed sensor for detecting the vehicle speed. Furthermore, the controller controls the output of the steering motor based on the driver steering input information and vehicle state information so that an adjusted torque for steering assistance is generated. In a conventional MDPS system, the controller controls the output of the steering motor by controlling the motor current applied to the steering motor.

[0009] At this time, the controller determines the amount of current based on information collected in the vehicle, i.e., driver steering input information and vehicle state information, and applies it to the steering motor. At this time, the motor is driven to generate a steering assist torque, which is a force for assisting the driver's steering force. On the other hand, in recent years, there has been a trend to widely apply DC motors instead of Brushless AC motors (BLAC motors) as steering motors (MDPS motors) in small and medium-sized vehicles in order to reduce costs.

[0010] However, unlike BLAC motors, DC motors have the disadvantage of poor NVH (Noise, Vibration & Harshness) due to their structure, as the brushes and commutator are in contact with each other when they operate. This is a cause of discomfort to the driver and is one of the factors that hinder the marketability of vehicles that use DC motors as steering motors, so there is a need to improve this issue.

[0011] In particular, in a vehicle that employs an MDPS system that uses a DC motor as a steering motor, it is necessary to improve the noise problem that occurs in the DC motor when the steering wheel is fixed (held) in a specific position while the vehicle is stopped, i.e., when the steering wheel is fixed in a position where a current equal to or greater than a specific value is applied to the DC motor.

[0012] When the DC motor of the MDPS system assists steering so that the steering wheel is fixed in a specific position while the vehicle is stopped, the controller applies a large current to the DC motor to generate force for steering assistance. In this case, if the brush and commutator are in a position that causes unstable contact, the DC motor may generate a buzzing noise.

[0013] 4 to 7 are diagrams for explaining problems that arise when a DC motor is used as a steering motor. FIG. 4 is a diagram showing the contact state between the brushes and the commutator in a known DC motor, FIG. 5 shows a stable contact state between the brushes and the commutator, and FIG. 6 is a diagram for explaining an unstable contact state between the brushes and the commutator.

[0014] In Figures 5 and 6, reference numeral 3 denotes a brush holder to which a brush 1 is fixed, and reference numeral 4 denotes a spring that elastically supports the brush 1 and the brush holder 3. In the DC motor, the brush 1 is elastically supported by the spring 4 and is constantly maintained in contact with the commutator 2 that rotates together with the rotor.

[0015] FIG. 7 is a diagram for explaining a state in which current fluctuation increases due to an unstable contact state between the brush 1 and the commutator 2 in a DC motor. When a large current is applied to the DC motor during steering assistance to fix the steering wheel in a specific position, unstable contact between the brush 1 and the commutator 2 may cause minute movements of the commutator, causing the current flow to repeatedly and momentarily fluctuate between "a" and "b" in Figure 6.

[0016] At this time, an instantaneous resistance fluctuation may occur, and as a result, a large current fluctuation may occur due to an instantaneous current fluctuation and resistance fluctuation between the brush 1 and the commutator 2. As shown in Figure 7, after the steering wheel is fixed, the current fluctuation on the right side increases.

[0017] When the current fluctuation phenomenon increases in this way, resonance occurs in the motor system due to the current frequency, which results in vibration along with a "humming" noise. When using a DC motor, a damping coupler that can reduce noise and vibration may be used to solve the above noise and vibration problems, but this causes an increase in costs. [Prior art documents] [Patent documents]

[0018] [Patent Document 1] JP 2009-44846 A Summary of the Invention [Problem to be solved by the invention]

[0019] Therefore, the present invention has been made to solve the above problems, and an object of the present invention is to provide an apparatus and method that can effectively solve the motor noise and vibration problems caused by unstable contact between the brushes and commutator of a DC motor in a vehicle that uses a DC motor instead of a BLAC motor as a steering motor. [Means for solving the problem]

[0020] In order to achieve the above object, according to one aspect of the present invention, there is provided a control device for an electric steering system, including a first sensor for detecting a vehicle speed or a wheel speed of a vehicle, a second sensor for detecting a steering angle caused by a driver's operation of a steering wheel, and a controller configured to selectively perform motor current control for reducing motor noise according to a motor applied current applied to a steering motor when the vehicle is determined to be in a stopped state from vehicle speed or wheel speed information detected by the first sensor and the steering wheel is determined to be in a fixed state from steering angle information detected by the second sensor. Here, the steering motor may be a DC motor.

[0021] Also, it is preferable that the controller is configured to determine that the steering wheel is fixed when the steering angle detected by the second sensor does not change for a preset reference time.

[0022] In addition, it is preferable that the controller is configured to perform motor current control to reduce the motor noise when the vehicle is stopped, the steering wheel is fixed, and the motor applied current is equal to or greater than a preset reference current value.

[0023] The controller may be configured to reduce a current applied to the steering motor to a preset control target value when performing motor current control to reduce the motor noise.

[0024] In addition, the controller reduces the current applied to the steering motor at a predetermined gradient until the current reaches the control target value when performing motor current control for reducing the motor noise. The control target value may be set as a motor applied current value at which noise is not generated in the steering motor of the vehicle and input to the controller.

[0025] The controller may be configured to reduce the current applied to the steering motor to the control target value and maintain the current at a constant value, and then increase the current applied to the steering motor when a driver steering input is determined from steering angle information detected by a second sensor.

[0026] In another aspect of the present invention, there is provided a control method for an electric steering system, including the steps of: detecting a steering angle due to operation of a steering wheel; determining by a controller that the vehicle is stopped based on vehicle speed or wheel speed information detected by the first sensor; determining by the controller, while the vehicle is stopped, that the steering wheel is fixed based on steering angle information detected by the second sensor; and, when the vehicle is stopped and the steering wheel is fixed, selectively performing motor current control by the controller to reduce motor noise in accordance with a motor applied current applied to a steering motor. Effect of the Invention

[0027] As a result, the steering system control device and control method of the present invention can effectively solve the motor noise and vibration problems caused by unstable contact between the brushes and commutator of the DC motor by simply applying simple control logic.

[0028] In particular, the motor noise and vibration that occurs when the steering wheel is fixed in a specific position while the vehicle is stopped can be resolved, and a damping coupler for reducing vibration and noise can be eliminated from the DC motor, which is expected to reduce costs. As a result, the marketability of a vehicle equipped with an electric steering system that uses a DC motor as the steering motor can be improved. [Brief description of the drawings]

[0029] [Figure 1] 1 is a block diagram showing a configuration of a control device of an electric steering system according to an embodiment of the present invention. [Diagram 2] 4 is a flowchart showing a control method for the electric steering system according to the embodiment of the present invention. [Diagram 3] 5A to 5C are diagrams illustrating an example of a current application state in the control method of the electric steering system according to the embodiment of the present invention. [Figure 4] FIG. 1 is a diagram for explaining a problem when a DC motor is used as a steering motor. [Diagram 5] FIG. 1 is a diagram for explaining a problem when a DC motor is used as a steering motor. [Figure 6] FIG. 1 is a diagram for explaining a problem when a DC motor is used as a steering motor. [Figure 7] FIG. 1 is a diagram for explaining a problem when a DC motor is used as a steering motor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. However, the present invention is not limited to the preferred embodiments described below and may be embodied in other forms.

[0031] Throughout the specification, when a part is described as "comprising" a certain element, this means that it may further include other elements, but not to the exclusion of other elements, unless specifically stated to the contrary.

[0032] The present invention aims to provide a control device and control method for an electric steering system that can effectively solve the problem of motor noise caused by unstable contact between the brushes and commutator of a steering motor in a vehicle that uses a DC motor as a steering motor for a steering assist device.

[0033] In particular, the present invention aims to provide a control device and control method for solving the problem of "humming" noise that may occur when a DC motor steering assist device is activated (a large amount of current above a certain level is applied to the motor) when the steering wheel is fixed in a specific position while the vehicle is stopped.

[0034] In order to achieve the above object, the present invention is configured with a control logic that controls the motor current to reduce noise (or noise and vibration) only when the DC motor of the steering assist device operates to fix the steering wheel while the vehicle is stopped.

[0035] In the present invention, the motor current control for reducing noise (or noise and vibration) is performed by the controller when all of the following conditions are met: the vehicle is stopped, the steering wheel is fixed, etc. Here, the steering wheel is fixed in place without being steered for a certain period of time after the driver has steered (i.e., rotated) the steering wheel to a certain level or more.

[0036] In addition, in the present invention, when the driver steers the steering wheel beyond a certain level, the current applied to the motor for steering assistance increases, so that when the driver steers (rotates) the steering wheel by a certain amount or more but does not steer the steering wheel further for a specified period of time, motor current control can be performed to reduce noise.

[0037] Here, when the driver turns the steering wheel by more than a certain amount as described above, it can be said that this is because the amount of current applied to the steering motor to assist steering has reached a level at which noise is likely to be generated.

[0038] With reference to the drawings, FIG. 1 is a block diagram showing the configuration of a control device for an electric steering system according to an embodiment of the present invention, and FIG. 2 is a flowchart showing a control method for the electric steering system according to an embodiment of the present invention. FIG. 3 is a diagram showing an example of a current application state in the control method for the electric steering system according to the embodiment of the present invention.

[0039] First, the control device according to an embodiment of the present invention is applied to an electric steering system that uses a DC motor as a steering motor, and as shown in FIG. 1, may include a first sensor 11 that detects a vehicle speed or a wheel speed, a second sensor 12 that detects a steering angle, and a controller 20 that controls a current applied to the steering motor 30 based on information detected by the first sensor 11 and the second sensor 12.

[0040] The first sensor 11 is a known vehicle speed sensor that detects vehicle speed, and since in a vehicle, the vehicle speed can also be obtained from the signal of a wheel speed sensor provided on each wheel, the first sensor 11 can also be a wheel speed sensor provided on each wheel of the vehicle. In a typical vehicle, wheel speed information can be obtained from signals of wheel speed sensors provided on a plurality of wheels, and the obtained wheel speeds can be converted into vehicle speed to obtain vehicle speed information.

[0041] In the present invention, the controller 20 can determine whether the vehicle is stopped or not from vehicle speed or wheel speed information obtained from the signal of the first sensor 11. For example, if the first sensor 11 is a wheel speed sensor provided on each of the left and right wheels, the controller 20 can confirm whether the vehicle is moving or stopped from the wheel speed values ​​of the left and right wheels obtained from the signals of the two wheel speed sensors.

[0042] In this way, the controller 20 can determine whether the vehicle is stopped using the vehicle speed detected by the first sensor 11, or using the vehicle speed converted from the wheel speed detected by the first sensor 11, or can directly determine whether the vehicle is stopped from the wheel speed detected by the first sensor 11.

[0043] In the present invention, the above control logic added to the controller 20 to reduce noise (or noise and vibration) is set to operate only when the vehicle is stopped. The second sensor 12 is a steering angle sensor used in a steering system, and the controller 20 receives a signal from the second sensor 12 to obtain steering angle information according to the driver's operation of the steering wheel.

[0044] In the present invention, the controller 20 can grasp the driver's steering intention from the steering angle detected by the second sensor 12, and in particular, can determine whether the steering wheel is fixed or not from the steering angle information detected by the second sensor 12.

[0045] In the present invention, the controller 20 can be set to determine that the driver has fixed the steering wheel if the steering angle (steering wheel angle) does not change during a preset reference time. Here, the reference time is a time that is input and stored in the controller 20 in advance and used.

[0046] The reference time is a tunable time that can be determined based on vehicle conditions, etc., and the present invention does not limit the reference time to a specific time, but it is preferable to set it to a time of less than 1 second so that the driver does not perceive the "whirling" motor noise.

[0047] In addition, in the present invention, in addition to the conditions that the vehicle is stopped and the steering wheel is fixed, when a motor current condition that may cause motor noise is satisfied, the controller 20 can be set to perform current control to reduce noise (or noise and vibration).

[0048] Here, the motor current conditions under which motor noise may occur are conditions for the amount of current applied to the steering motor 30, and can be set as current conditions under which the "whirling" noise and the resulting vibrations may occur in the steering motor 30 for the reasons described above.

[0049] In the present invention, the controller 20 is an electric steering system controller (MDPS ECU) 20, and in a typical electric steering system, the controller 20 determines a current target value in accordance with driver steering input information and vehicle state information, and in order to control the current applied to the steering motor 30, the controller 20 itself stores the current to be applied to the steering motor 30.

[0050] In the present invention, the controller 20 is arranged to constantly monitor the current applied to the steering motor 30. At this time, a condition that the current applied to the motor is equal to or greater than a preset reference current value can be set in the controller 20 as a motor current condition. Ultimately, in the present invention, the controller 20 performs motor current control to reduce noise when the following conditions are met: the vehicle is stopped, the steering wheel is fixed, and the monitored motor applied current is equal to or greater than the reference current value.

[0051] In an electric steering system to which the present invention is applied, when a current greater than a certain level is applied to the DC motor serving as the steering motor 30, the current tends to fluctuate significantly, easily generating a buzzing noise. For example, in an electric steering system, if the maximum current that can be applied to the DC motor that is the steering motor 30 is 70 amperes, the DC motor is likely to make a whirring noise when 50 amperes or more are applied.

[0052] In the present invention, the control logic is configured to confirm the current value (amperes) at which the "humming" noise is likely to occur in the vehicle as described above, set that current value as a reference current value in the controller 20, and have the controller 20 monitor and confirm the motor applied current. When a current equal to or greater than the set reference current value is applied to the steering motor 30, it is determined that the motor current condition is satisfied.

[0053] The control process according to the present invention will now be described with reference to FIG. First, the controller 20 obtains the current vehicle speed or wheel speed information from the signal of the first sensor 11, and obtains steering angle information from the signal of the second sensor 12 (S1). Next, the controller 20 determines whether the vehicle is currently stopped or not based on the vehicle speed or wheel speed information (S2).

[0054] Here, when the controller 20 determines that the vehicle is stopped, it determines whether or not the motor current control condition for reducing the noise (or noise and vibration) of the steering motor 30 is satisfied, based on the steering angle obtained from the signal of the second sensor 12 and the monitored motor applied current.

[0055] At this time, the controller 20 checks whether the steering angle has not changed for a reference time (S3), then checks the current applied to the motor (S4), and then checks whether the monitored current applied to the motor is equal to or greater than the reference current (S5). Here, if the steering angle does not change during the reference time, the controller 20 determines that the steering wheel fixed condition is satisfied, and if the monitored motor applied current is equal to or greater than the reference current value, the controller 20 determines that the motor current condition is satisfied.

[0056] In other words, it is determined that the steering wheel is in a fixed state, that is, the driver has not rotated the steering wheel for a reference time and has fixed it in a specific position, and that a current larger than a reference current value that may cause noise is being applied to the steering motor 30, which is a DC motor.

[0057] In this way, when the vehicle stop condition, the steering wheel fixed condition, and the specified motor current condition (motor large current application condition) are all satisfied, the controller 20 performs motor current control to reduce noise (or noise and vibration), and in this case, reduces the current applied to the steering motor 30 to a preset control target value (S6).

[0058] Here, the control target value is determined as a current value at which no noise is generated in the DC motor, which is the steering motor 30 in the vehicle, and can be set to a value lower than 50 amperes, for example. Referring to FIG. 3, when the vehicle is stopped, if the driver does not steer (turn) the steering wheel but keeps it fixed for a time ▲d▼ (sec) that is equal to or greater than a reference time (e.g., 1 second), and the monitored motor applied current is ▲a▼ amperes that is greater than a reference current value ▲b▼ amperes (e.g., 50 amperes), the controller 20 reduces the motor applied current to a preset control target value ▲c▼ amperes.

[0059] In this case, the controller 20 can be set to quickly decrease the motor applied current at a predetermined constant gradient from the current motor applied current ▲a▼ amperes to the control target value ▲c▼ amperes. Here, the gradient at which the current is changed can be appropriately tuned according to the vehicle conditions, etc., so as to minimize the sense of strangeness felt by the driver.

[0060] In this way, in the present invention, when the vehicle stop condition, the steering wheel fixed condition, and the specified motor current condition are all satisfied, motor current control is performed to quickly reduce the motor applied current to the set control target value.

[0061] In addition, after reducing the motor application current to the control target value, while the motor application current is being maintained at the control target value, if a driver steering input is determined from the steering angle information detected by the second sensor 12 at time ▲e▼ in Figure 3, that is, if it is determined that the driver has turned (steered) the steering wheel, the controller 30 quickly increases the motor application current to the current value determined during normal steering control. By quickly restoring the current value in this manner, normal steering assistance by the steering motor 30 is performed.

[0062] Then, if any one of the vehicle stop condition, steering wheel fixation condition, and specified motor current condition (condition for applying a large current equal to or greater than a reference current value) is not satisfied, the controller 20 performs normal steering control that controls the motor application current and the output of the steering motor 30 in response to the driver steering input information and vehicle state information, without performing motor current control to reduce the motor application current to a control target value (S7).

[0063] In this way, in the present invention, when the steering wheel is fixed while the vehicle is stopped and the current applied to the motor has increased to a noise generation level, the current applied to the motor is quickly reduced, thereby making it possible to prevent the generation of noise and vibration. When the current applied to the motor is reduced as described above, the position of the motor's commutator is shifted slightly, changing the unstable contact state to a stable contact state, and as a result, the "whirling" noise is no longer generated.

[0064] Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the present invention defined in the appended claims are also included in the scope of the present invention. [Explanation of symbols]

[0065] 11 First Sensor 12 Second Sensor 20 Controller 30 Steering motor

Claims

1. A first sensor for detecting a vehicle speed or a wheel speed of a vehicle; a second sensor for detecting a steering angle caused by an operation of a steering wheel by a driver; a controller configured to perform motor current control for reducing motor noise in accordance with a motor applied current applied to a steering motor when the controller determines that the vehicle is stopped from vehicle speed or wheel speed information detected by the first sensor, and determines that the steering wheel is fixed from steering angle information detected by the second sensor while the driver is holding the steering wheel after steering the steering wheel by a certain amount or more, The steering motor is a brushed DC motor, The control device for an electric steering system, wherein the controller is configured to perform motor current control to reduce motor noise when the vehicle is stopped, the steering wheel is fixed, and the motor applied current is equal to or greater than a preset reference current value.

2. 2. The control device for an electric steering system according to claim 1, wherein the controller determines that the steering wheel is fixed when the steering angle detected by the second sensor does not change for a preset reference time.

3. 2. The control device for an electric steering system according to claim 1, wherein the controller reduces the current applied to the steering motor to a preset control target value when performing motor current control to reduce the motor noise.

4. 2. The control device for an electric steering system according to claim 1, wherein the controller reduces the current applied to the steering motor to a preset control target value when performing motor current control to reduce the motor noise.

5. 5. The control device for an electric steering system according to claim 4, wherein the controller reduces the current applied to the steering motor at a predetermined gradient until the current reaches the control target value when performing motor current control to reduce the motor noise.

6. 5. The control device for an electric steering system according to claim 4, wherein the control target value is set as a motor applied current value at which noise is not generated in the steering motor of the vehicle, and is input to the controller.

7. 5. The control device for an electric steering system according to claim 4, wherein the controller reduces the current applied to the steering motor to the control target value and maintains the current at a constant value, and then increases the current applied to the steering motor when a driver's steering input is determined from steering angle information detected by the second sensor.

8. A step of detecting a steering angle due to an operation of a steering wheel; A step in which a controller determines that the vehicle is currently in a stopped state based on vehicle speed or wheel speed information detected by a first sensor; a step of the controller determining that the steering wheel is in a fixed state based on steering angle information detected by a second sensor when the vehicle is stopped and the driver steers the steering wheel by a certain amount or more and then the driver assists the steering wheel; performing a motor current control for reducing motor noise according to a motor applied current applied to a steering motor by the controller when the vehicle is stopped and the steering wheel is fixed; Including, The steering motor is a brushed DC motor, a control method for an electric steering system, the control device performing a motor current control to reduce motor noise when the motor applied current is equal to or greater than a preset reference current value while the vehicle is stopped and the steering wheel is fixed.

9. 9. The method for controlling an electric steering system according to claim 8, wherein the controller determines that the steering wheel is fixed when the steering angle detected by the second sensor does not change for a preset reference time.

10. 9. The method for controlling an electric steering system according to claim 8, wherein the controller reduces a current applied to the steering motor to a preset control target value when performing motor current control for reducing the motor noise.

11. 9. The method for controlling an electric steering system according to claim 8, wherein the controller reduces a current applied to the steering motor to a preset control target value when performing motor current control for reducing the motor noise.

12. 12. The method of claim 11, wherein the controller reduces the current applied to the steering motor at a predetermined gradient until the current reaches the control target value when performing motor current control to reduce the motor noise.

13. 12. The method of claim 11, wherein the control target value is set to a motor applied current value that does not cause noise in the steering motor of the vehicle and is input to the controller.

14. The controller, reducing the current applied to the steering motor to the control target value and then maintaining the current constant; 12. The method for controlling an electric steering system according to claim 11, wherein the motor applied current is increased when thereafter a steering input from the driver is detected from steering angle information detected by the second sensor.

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