Rear wheel steering system

Abstract

This invention discloses a rear-wheel steering system. A rear-wheel steering motor generates rotational force. A motion converter has a conversion section coupled to the rear-wheel steering motor and is configured to convert the rotational force transmitted from the rear-wheel steering motor into linear motion. MR fluid is applied to the conversion section. An inverter controls the drive of the rear-wheel steering motor. A magnetic switch works in conjunction with the inverter to change the magnetic field to selectively provide a magnetic field to the MR fluid of the motion converter.

Description

Technical Field

[0001] The present invention generally relates to a rear-wheel steering system that can operate with high efficiency when the rear-wheel steering motor is input in the forward direction, while reliably performing self-locking when there is no input from the rear-wheel steering motor or when the rear-wheel steering motor is input in the reverse direction. Background Technology

[0002] Rear wheel steering (RWS) is designed to enable the rear wheels to steer in the same direction as the front wheels. At lower speeds, the RWS system controls the rear wheel steering angle to be opposite to or in the opposite direction to the front wheel steering angle to reduce the turning radius. At higher speeds, the RWS system controls the rear wheel steering angle to be in the same direction as or in the same direction as the front wheel steering angle to improve driving stability.

[0003] When the rear wheels are reversed, the rear-wheel steering system struggles to achieve straight-line driving due to rear-wheel instability. Therefore, it is necessary to achieve rear-wheel driving stability and prevent reverse driving in order to provide fault protection against rear-wheel steering system malfunctions.

[0004] Therefore, the rear-wheel steering system of the relevant technology uses a self-locking gear mechanism including a lead screw.

[0005] The lead screw has a self-locking characteristic, where the reverse efficiency is zero (0) under certain conditions (e.g., friction characteristics and lead angle). However, under these conditions, there is a problem that the forward efficiency is also significantly reduced.

[0006] Therefore, as the positive efficiency of the gear mechanism decreases, the output power of the motor needs to be increased accordingly, which also increases the size, cost, and energy loss of the motor.

[0007] In particular, RWS systems that have the same steering angle as the front wheels within the current range of ±3° of the rear wheel steering angle, or rear wheel steering systems that support large rear wheel steering angles and facilitate full motion, require greater output power, and therefore, essentially require improved positive efficiency.

[0008] To overcome this drawback of reduced positive efficiency, a device has been proposed that uses a mechanism with higher efficiency than a lead screw (e.g., a ball screw or planetary roller screw) and can additionally achieve a locking operation under certain conditions by controlling a solenoid valve.

[0009] However, according to this device, the locking is activated intermittently, and additional operation of the solenoid valve is required. Therefore, there is a problem of reduced responsiveness in the rear-wheel steering system.

[0010] The content contained in the Background section is only intended to enhance the understanding of the general background of the invention and should not be construed as an admission of prior art known to those skilled in the art or any form of implication. Summary of the Invention

[0011] Aspects of the present invention aim to provide a rear-wheel steering system that can operate efficiently with a positive input from the rear-wheel steering motor, while reliably performing self-locking without a rear-wheel steering motor input or with a reverse input from the rear wheels.

[0012] In various aspects of the present invention, a rear-wheel steering system is provided, comprising: a rear-wheel steering motor configured to generate rotational force; a motion converter having a conversion section coupled to the wheel steering motor and configured to convert the rotational force transmitted from the rear-wheel steering motor into linear motion via a magnetorheological (MR) fluid applied to the conversion section; an inverter connected to the wheel steering motor and configured to control the drive of the rear-wheel steering motor; and a magnetic switch connected to the inverter and configured to cooperate with the inverter to change the magnetic field to selectively provide a magnetic field to the MR fluid of the motion converter.

[0013] When current is applied to the inverter, the magnetic field of the magnetic switch can be eliminated from the MR fluid. When no current is applied to the inverter, the magnetic field of the magnetic switch can be supplied to the MR fluid.

[0014] The magnetic switch may include: an electromagnet connected to an inverter and magnetized in response to receiving current from the inverter to generate a magnetic field; and a permanent magnet connected via a conductive connector to a first end and a second end of the core of the electromagnet.

[0015] The permanent magnet is positioned between the electromagnet and the MR fluid.

[0016] MR fluid can be applied between a guide nut configured to rotate by the rotational force of a rear wheel steering motor and a lead screw engaged with the guide nut and configured to move linearly in response to the rotation of the guide nut. A magnetic switch can be configured to be wound around the guide nut.

[0017] The permanent magnet can be positioned closer to the guide nut than the electromagnet.

[0018] According to various exemplary embodiments of the present invention, when the rear wheel steering motor is driven, power is transmitted to the rear wheels through the soft state or softening of the MR fluid. When the rear wheel steering motor is not driven, reverse input to the rear wheels is blocked to achieve self-locking operation.

[0019] In addition, when the rear wheel steering system is de-energized, the MR fluid can remain in a hardened state to enable the self-locking function and also obtain fault protection function.

[0020] Furthermore, compared to self-locking mechanisms in related technologies, the locking operation can be non-intermittent and can be performed quickly to improve operability. Gearbox efficiency can be improved, thereby reducing motor capacity. Self-locking operation can be achieved without adding controllers or sensors, reducing cost and weight.

[0021] The methods and apparatus of the present invention have other features and advantages, which will become apparent from the accompanying drawings and the following detailed description, which together serve to explain certain principles of the invention, or will be set forth in more detail in the drawings and detailed description. Attached Figure Description

[0022] Figure 1 This is a diagram illustrating the softening of MR fluid in response to driving a rear wheel steering motor according to various exemplary embodiments of the present invention;

[0023] Figure 2 This is a diagram illustrating the hardening of MR fluid in response to an undriven rear wheel steering motor according to various exemplary embodiments of the present invention;

[0024] Figure 3 It is shown Figure 1 A diagram showing the operational relationship of the magnetic switches; and

[0025] Figure 4 It is shown Figure 2 A diagram illustrating the operational relationship of the magnetic switch.

[0026] It is understood that the accompanying drawings are not necessarily drawn to scale, but rather present a slightly simplified representation of various features illustrating the basic principles of the invention. Specific design features of the invention included in this disclosure, including, for example, specific dimensions, orientations, positions, and shapes, will be determined in part by the particular intended application and environment of use.

[0027] In the accompanying drawings, reference numerals refer to the same or equivalent parts of the invention in multiple figures. Detailed Implementation

[0028] Reference will now be made in detail to various exemplary embodiments of the invention illustrated in the accompanying drawings and described below. Although the invention will be described in conjunction with exemplary embodiments thereof, it will be understood that this disclosure is not intended to limit the invention to those exemplary embodiments. On the other hand, the invention is intended to cover not only the exemplary embodiments thereof, but also various alternatives, modifications, equivalents and other embodiments that may be included within the spirit and scope of the invention as defined in the appended claims.

[0029] In the following description, various exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0030] Figure 1 This is a diagram illustrating the softening of the magnetorheological (MR) fluid 250 in response to driving the rear wheel steering motor 100 according to various exemplary embodiments of the present invention. Figure 2 This is a diagram illustrating the hardening of MR fluid 250 in response to an undriven rear wheel steering motor 100 according to various exemplary embodiments of the present invention.

[0031] Reference Figure 1 and Figure 2 A rear-wheel steering system according to various exemplary embodiments of the present invention may include: a rear-wheel steering motor 100 that generates rotational force; a motion converter 200 having a conversion section coupled to the wheel steering motor and configured to convert the rotational force transmitted from the rear-wheel steering motor 100 into linear motion by means of an MR fluid 250 applied to the conversion section; an inverter 300 configured to control the drive of the rear-wheel steering motor 100; and a magnetic switch 400 configured to cooperate with the circuitry of the inverter 300 to change the magnetic field to selectively provide a magnetic field to the MR fluid 250.

[0032] Here, the motion converter 200 includes a motor pulley 210, the shaft of which is connected to the output shaft of the rear wheel steering motor 100, allowing the motor pulley 210 to rotate. The motor pulley 210 and the guide nut 230 are connected by a belt 220, allowing the guide nut 230 to rotate.

[0033] Furthermore, the guide nut 230 is rotatably supported by the bearing 260. The lead screw 240 extends through the guide nut 230 for linear movement.

[0034] That is, when the rear wheel steering motor 100 is driven, the motor pulley 210 rotates, causing the guide nut 230 to rotate responsively via the belt 220. In response to the rotation of the guide nut 230, the lead screw 240 converts to linear motion and moves laterally, providing the steering angle of the rear wheels.

[0035] Here, a lead screw 240 with a relatively large lead angle is used as a gear mechanism to convert the rotation of the rear wheel steering motor 100 into linear motion, thereby achieving higher forward efficiency than the screws of related technologies.

[0036] Furthermore, the MR fluid 250 is a gel-type material, such as MR grease, with a magnetizing component. When an electric current flows through this MR fluid 250, the MR fluid 250 aligns in a specific array, thus hardening while being magnetized. When no current flows, the MR fluid 250 softens or remains in a soft gel state, performing functions similar to grease.

[0037] In addition, inverter 300 is used to control the drive of rear wheel steering motor 100. When current flows through inverter 300 in response to a signal applied to the insulated gate bipolar transistor (IGBT) to control rear wheel steering motor 100, the circuit of inverter 300 supplies current to magnetic switch 400.

[0038] Therefore, the magnetic switch 400 is configured to control the magnetic field applied to the MR fluid 250 according to the current supplied through the inverter 300, while changing the magnetic field.

[0039] According to the above configuration, when the rear wheel steering motor 100 is driven, the magnetic field of the magnetic switch 400 is changed by the current flowing through the inverter 300, causing the MR fluid 250 to soften. Conversely, when the rear wheel steering motor 100 is not driven, the current supply through the inverter 300 stops, therefore, the magnetic field of the magnetic switch 400 changes, causing the MR fluid 250 to harden.

[0040] Therefore, when driving the rear wheel steering motor 100, the motion converter 200 transmits power to the rear wheels via the softened MR fluid 250. In the case of rear wheel reverse input, the self-locking function of the motion converter 200 can be reliably achieved by the hardened MR fluid 250, and a rear wheel steering (RWS) system supporting large rear wheel steering angles can be realized by utilizing the front wheel shift-by-wire (SBW) system.

[0041] Furthermore, not only when the rear wheel steering motor 100 is not driven, but also in the event of a power outage, the hardened MR fluid 250 can automatically achieve a self-locking function, and also provide fault protection.

[0042] Furthermore, the present invention can be configured to eliminate the magnetic field of the magnetic switch 400 from the MR fluid 250 when current is applied to the inverter 300, and to provide the magnetic field of the magnetic switch 400 to the MR fluid 250 when no current is applied to the inverter 300.

[0043] That is, when the rear wheel steering motor 100 is driven, the magnetic switch 400 can eliminate the magnetic field already supplied to the MR fluid 250 to soften the MR fluid 250 before the rear wheel steering motor 100 actually moves. Therefore, it is required that the operation of the magnetic switch 400 precedes the driving of the rear wheel steering motor 100.

[0044] Therefore, if a controller is additionally provided for controlling the magnetic switch 400, it is necessary to sense the movement of the rear wheel steering motor 100 and to make complex and rapid decisions, such as control timing management for operating the magnetic switch 400 before sensing.

[0045] However, according to various exemplary embodiments of the present invention, when the magnetic switch 400 works in conjunction with the inverter 300 that controls the rear wheel steering motor 100 and the operation of the magnetic switch 400 is controlled by the current from the inverter 300, the current flows through the magnetic switch 400 first and then through the rear wheel steering motor 100 to activate the magnetic switch 400 and change the magnetic field before actually driving the rear wheel steering motor 100, thereby softening the MR fluid 250.

[0046] Therefore, the magnetic switch 400 can be operated before the rear wheel steering motor 100 is driven, without adding, for example, a separate high-performance controller or sensor, thereby reliably driving the rear wheel steering motor 100 while reducing costs.

[0047] Figure 3 It is shown Figure 1 The diagram shows the operational relationship of the magnetic switch 400. Figure 4 It is shown Figure 2 The diagram shows the operational relationship of the magnetic switch 400.

[0048] Reference Figure 3 and Figure 4 The magnetic switch 400 includes: an electromagnet 410, which is magnetized in response to a current supplied by the inverter 300; and a permanent magnet 420, which is connected to both ends of the iron core 412 of the electromagnet 410 via a conductive connector 430.

[0049] Furthermore, the permanent magnet 420 is a structure disposed between the electromagnet 410 and the MR fluid 250.

[0050] For example, coil 414 is wound around iron core 412 to form electromagnet 410, and both ends of coil 414 are connected to inverter 300 so that current can flow through coil 414.

[0051] In addition, the two ends of the iron core 412 and the two ends of the permanent magnet 420 are connected in parallel through a conductive connector 430, so that current can flow through the electromagnet 410 and the permanent magnet 420.

[0052] like Figure 3 As shown, when current flows through the electromagnet 410 in response to the operation of the inverter 300 circuit, a magnetic field is generated only between the electromagnet 410 and the permanent magnet 420, and no magnetic field is generated outside the electromagnet 410 or the permanent magnet 420. Therefore, the magnetic field has no effect on the MR fluid 250.

[0053] Therefore, the MR fluid 250 softens to act as a lubricant, allowing the power provided by the rear wheel steering motor 100 to be transmitted to the rear wheels via the motion converter 200.

[0054] On the contrary, such as Figure 4As shown, when no current flows through the electromagnet 410 in response to the inoperability of the inverter 300 circuit, the magnetic field of the permanent magnet 420 is not only applied to the electromagnet 410, but also directed towards the MR fluid 250, affecting the MR fluid 250.

[0055] Therefore, the MR fluid 250 hardens, thus reliably enabling the self-locking operation of the motion converter 200.

[0056] In addition, refer to Figure 2 According to various exemplary embodiments of the present invention, MR fluid 250 may be applied between a guide nut 230 configured to rotate by the rotational force of the rear wheel steering motor 100 and a lead screw 240 configured to move linearly in response to the rotation of the guide nut 230, and magnetic switch 400 may be configured to be wound around the guide nut 230.

[0057] Furthermore, the permanent magnet 420 can be positioned closer to the guide nut 230 than the electromagnet 410.

[0058] That is, the guide nut 230 is made of a conductor, and the MR fluid 250 is applied between the guide nut 230 and the lead screw 240.

[0059] Therefore, when no current flows through the electromagnet 410, the magnetic field of the permanent magnet 420 is applied to the guide nut 230, affecting the MR fluid 250 applied between the guide nut 230 and the lead screw 240.

[0060] Therefore, the magnetic field is applied not only to the electromagnet 410 but also to the MR fluid 250, affecting the MR fluid 250. As a result, the MR fluid 250 hardens, thus reliably achieving the self-locking operation of the motion converter 200.

[0061] The operational relationships of a rear-wheel steering system according to various exemplary embodiments of the present invention will be described below.

[0062] like Figure 1 As shown, when the inverter 300 is operated to drive the rear wheel steering motor 100, current flows through the inverter 300.

[0063] Therefore, the current generated in the inverter 300 is supplied to the electromagnet 410 of the magnetic switch 400, magnetizing the electromagnet 410.

[0064] Therefore, the current flowing through the electromagnet 410 generates a magnetic field only between the electromagnet 410 and the permanent magnet 420, and the magnetic field does not point towards the guide nut 230, so it has no effect on the MR fluid 250 applied between the guide nut 230 and the lead screw 240.

[0065] Therefore, the MR fluid 250 softens and is provided as grease between the guide nut 230 and the lead screw 240.

[0066] In addition, in response to the operation of the inverter 300, the rear wheel steering motor 100 is controlled to operate.

[0067] Here, since current flows from the inverter 300 to the magnetic switch 400 before driving the rear wheel steering motor 100, a smooth motion conversion can be achieved between the guide nut 230 and the lead screw 240. Therefore, the power provided by the rear wheel steering motor 100 is reliably transmitted to the rear wheels via the motion converter 200.

[0068] On the contrary, such as Figure 2 As shown, when the operation of inverter 300 stops, no current flows through inverter 300, and therefore no current is supplied to electromagnet 410.

[0069] Therefore, as Figure 4 As shown, the magnetic field of the permanent magnet 420 is applied not only to the electromagnet 410, but also to the guide nut 230, affecting the MR fluid 250 applied between the guide nut 230 and the lead screw 240.

[0070] Therefore, the MR fluid 250 hardens, thus preventing motion conversion between the guide nut 230 and the lead screw 240. Consequently, a self-locking operation of the motion converter 200 is achieved.

[0071] As described above, according to various exemplary embodiments of the present invention, when the rear wheel steering motor 100 is driven, power is transmitted to the rear wheels through the softening of the MR fluid 250. When the rear wheel steering motor 100 is not driven, the reverse input to the rear wheels is blocked, achieving self-locking operation. Thus, an RWS system supporting large rear wheel steering angles can be realized using the front wheel SBW system.

[0072] Furthermore, when the rear wheel steering system is de-energized, the MR fluid 250 can remain in a hardened state to enable the self-locking function. Therefore, a fault protection function is also possible.

[0073] Furthermore, compared to self-locking mechanisms in related technologies, the locking operation can be non-intermittent and can be performed quickly to improve operability. Gearbox efficiency can be improved, thereby reducing motor capacity. Self-locking operation can be achieved without adding controllers or sensors, reducing cost and weight.

[0074] Furthermore, terms related to control devices, such as "controller," "control unit," "control device," or "control module," refer to hardware devices including a memory and a processor configured to execute one or more steps interpreted as an algorithmic structure. The memory stores algorithmic steps, and the processor executes these steps to perform one or more processes of methods according to various exemplary embodiments of the invention. A control device according to exemplary embodiments of the invention can be implemented using a non-volatile memory configured to store algorithms for controlling the operation of various components of a vehicle or data regarding software commands for executing the algorithms, and a processor configured to perform the aforementioned operations using the data stored in the memory. The memory and processor can be separate chips. Alternatively, the memory and processor can be integrated into a single chip. The processor can be implemented as one or more processors. The processor can include various logic circuits and arithmetic circuits, can process data according to a program provided by the memory, and can generate control signals based on the processing results.

[0075] The control device may be at least one microprocessor operated by a predetermined program, which may include a series of commands for performing the methods disclosed in the various exemplary embodiments of the present invention described above.

[0076] The invention described above can also be embodied as computer-readable code on a computer-readable recording medium. A computer-readable recording medium is any data storage device that can store data that can subsequently be read by a computer system. Examples of computer-readable recording media include hard disk drives (HDDs), solid-state drives (SSDs), silicon disk drives (SDDs), read-only memory (ROM), random access memory (RAM), CD-ROMs, magnetic tapes, floppy disks, optical data storage devices, and implementations as carrier waves (e.g., transmitted over the Internet).

[0077] In various exemplary embodiments of the present invention, each of the above operations may be performed by a control device, and the control device may be configured as a plurality of control devices or an integrated single control device.

[0078] In various exemplary embodiments of the present invention, the control device may be implemented in hardware or software, or in a combination of hardware and software.

[0079] For ease of interpretation and precise definition of the appended claims, the features are described using the terms “upper,” “lower,” “inner,” “outer,” “up,” “lower,” “upward,” “downward,” “front,” “back,” “behind,” “inner side,” “outer side,” “inward,” “outer,” “within,” “outside,” “forward,” and “backward”, with reference to the locations shown in the figures for exemplary embodiments. It will be further understood that the term “connection” or its derivatives refer to both direct and indirect connections.

[0080] For illustrative and descriptive purposes, the foregoing description of specific exemplary embodiments of the invention has been disclosed. These descriptions are not intended to be exhaustive or to limit the invention to the specific forms disclosed, and it will be apparent that many modifications and variations are possible in light of the foregoing teachings. The exemplary embodiments selected and described are intended to explain certain principles of the invention and its practical application, enabling others skilled in the art to implement and utilize various exemplary embodiments of the invention, as well as various alternatives and modifications thereof. The scope of the invention is intended to be defined by the appended claims and their equivalents.

Claims

1. A wheel steering system, comprising: The wheel steering motor generates rotational force; The motion converter has a conversion section connected to the wheel steering motor, and converts the rotational force transmitted from the wheel steering motor into linear motion by a magnetorheological fluid, i.e., an MR fluid, applied to the conversion section; An inverter, connected to the wheel steering motor, and controlling the drive of the wheel steering motor; and A magnetic switch, connected to the inverter and cooperating with the inverter, alters the magnetic field to selectively supply the magnetic field to the MR fluid of the motion converter. The magnetic switch includes: An electromagnet, connected to the inverter, and magnetized in response to receiving current from the inverter to generate the magnetic field; and A permanent magnet is connected to the first and second ends of the core of the electromagnet via a conductive connector.

2. The wheel steering system according to claim 1, wherein, When current is applied to the inverter, the magnetic field of the magnetic switch is eliminated from the MR fluid, and When no current is applied to the inverter, the magnetic field of the magnetic switch is provided to the MR fluid.

3. The wheel steering system according to claim 1, wherein, The first and second ends of the iron core are connected in parallel with the first and second ends of the permanent magnet through the conductive connector.

4. The wheel steering system according to claim 1, wherein, The permanent magnet is disposed between the electromagnet and the MR fluid.

5. The wheel steering system according to claim 1, wherein, The conversion section of the motion converter includes a guide nut and a lead screw, and The MR fluid is applied between the guide nut, which is rotated by the rotational force of the wheel steering motor, and the lead screw, which engages with the guide nut and moves linearly in response to the rotation of the guide nut.

6. The wheel steering system according to claim 5, wherein, The magnetic switch is configured to be wound around the guide nut.

7. The wheel steering system according to claim 5, wherein, The permanent magnet is positioned closer to the guide nut than the electromagnet.

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