Rear-wheel steering system

Abstract

To provide a rear-wheel steering device with a wide displacement measurement range and a rational configuration. [Solution] A rear wheel steering device A comprising a housing 4, a drive unit M, a rod 3 that reciprocates along the axis X in a non-rotating state by the drive unit M, and a displacement detection unit S that detects the displacement of the rod 3, wherein the displacement detection unit S comprises a magnet 24 fixed to the rod 3, a pair of elements 25 dispersed along the axis X and arranged such that the ranges for detecting the magnetic field strength of the magnet 24 overlap, and a control unit C that calculates the position of the magnet 24 along the axis X relative to the pair of elements 25 from the detection results of at least one of the elements 25, wherein the distance between the furthest ends of the combination of the ends of one element and the other of the pair of elements 25 is defined as the element-to-element distance, and the length of the magnet 24 along the axis X is configured to be shorter than the element-to-element distance.

Description

Technical Field

[0001] The present invention relates to a rear-wheel steering device capable of measuring the displacement of a rod by reciprocating the rod by a drive unit and distributing and arranging a magnet and an element for measuring the magnetic field strength of the magnet on the relatively moving rod and housing.

Background Art

[0002] Conventionally, as such a rear-wheel steering device, for example, there is one shown in Patent Document 1 (see FIGS. 1 from

[0026] to

[0041] ). <​​​​​​​​​​​​​​​​​​​​​​​​​

[0006] In the conventional rear-wheel steering device described above, which can prevent rattling of the magnetic block 50 when the rod 2 moves, the accuracy of detecting the displacement of the rod 2 is improved somewhat. However, since the displacement sensor 5a and the magnetic block 50 are only provided one each inside the housing 1b, there are certain limitations to the detection range of the magnetic block 50.

[0007] For example, in conventional technology, if you want to increase the stroke amount, you need to extend the total length of the magnet in proportion to the desired stroke amount. This is because in order to ensure the accuracy of magnetic field detection by the displacement sensor 5a, the distance between the magnet and the displacement sensor 5a must be kept within a predetermined distance. As a result, the size of the displacement detection device 5 and the rear wheel steering device increases, worsening their mountability, and also leading to increased manufacturing costs for the magnet and magnet block.

[0008] Thus, conventional rear-wheel steering systems have various challenges that need to be addressed in order to increase the displacement measurement range, and there has been a need for a rear-wheel steering system with a wide displacement measurement range and a rational configuration. [Means for solving the problem]

[0009] (Feature composition) The characteristic configuration of the rear-wheel steering device according to the present invention is: In the housing, The drive unit and The aforementioned drive unit provides a rod that moves back and forth along its own axis in a non-rotating state, The system includes a displacement detection unit for detecting the displacement of the aforementioned rod, The displacement detection unit, A magnet fixed to the rod and moving back and forth together with the rod, A pair of elements are dispersed along the axis and arranged such that the ranges for detecting the strength of the magnetic field formed by the magnet overlap, The system includes a control unit that calculates the position of the magnet along the axis of the pair of elements from the detection result of at least one of the pair of elements, The key point is that when the distance between the ends of one element of the pair and the end of the other element of the pair is defined as the distance between the ends in the furthest possible combination, the length of the magnet along the axis is configured to be shorter than the distance between the elements.

[0010] (effect) Conventional rear-wheel steering systems, which use a detection method with one magnet and one element, required increasing the length of the magnet to expand the detection range. In contrast, this rear-wheel steering system has multiple elements arranged around the magnet, allowing the elements that detect the magnet's magnetic field to be sequentially rotated as the magnet moves back and forth. The magnetic field detection range of a single element is determined by the size of the magnet and the strength of the magnetic field, but by overlapping the magnetic field detection ranges of a pair of elements, the magnetic field detection range of the magnet is increased.

[0011] By incorporating multiple elements in this way, the magnet's position detection range can be expanded while maintaining a small magnet size. Maintaining a compact magnet size reduces the likelihood of interference between the magnet and other objects during the reciprocating motion of the rod to which it is attached, making it easier to increase the rod's reciprocating stroke.

[0012] With this configuration, the rear wheel steering angle can be increased while maintaining compact device dimensions, resulting in a rear wheel steering system with excellent mountability.

[0013] In particular, in this configuration, when the distance between the ends of one element and the other element in the pair is defined as the distance between the ends in the furthest possible combination, the length of the magnet along the axis is configured to be shorter than the distance between elements. In this case, when the magnet moves back and forth between both elements and transitions from a detection state by one element to a detection state by the other element, the magnet does not need to simultaneously and completely overlap both elements in a direction perpendicular to the axis. Therefore, the length of the magnet in the axial direction can be shortened, simplifying the configuration of the displacement detection unit and allowing the magnet to move more smoothly.

[0014] (Feature composition) In the rear-wheel steering device according to the present invention, the length of the magnet can be set to a length such that the magnet and the pair of elements do not overlap simultaneously in a direction perpendicular to the axis when the magnet is positioned between the pair of elements.

[0015] (effect) This configuration utilizes the fact that the magnetic field detection range of a magnet from a single element extends to both sides of the element along its axis. In other words, for a pair of elements placed in a predetermined position, the magnet does not necessarily need to overlap with both elements in a direction perpendicular to the axis. When the magnet is located between the pair of elements, it can be positioned so as not to overlap with either element. Furthermore, even when the magnet is located outside of one of the elements, it can be displaced to a position where it does not overlap in a direction perpendicular to the axis.

[0016] Therefore, when the elements are set at a predetermined distance from each other, it is possible to use only one magnet while shortening the length of the magnet. The distance between the magnet and the element along the axis can be appropriately set, for example, based on the magnetic field strength value detected by the element.

[0017] (Feature composition) In the rear-wheel steering device according to the present invention, it is advantageous that when the rod is in the reference position with respect to the housing, the position of the magnet along the axis is set to be different from the central position between the pair of elements in the same direction.

[0018] (Effect) For the position detection of the magnet, the element on the side where the distance from the center position of the magnet to each element is shorter, that is, the element with a higher detected magnetic field strength value, is used. In that case, by making the distances between the magnet and the respective elements different at the reference position of the rod, the element to be used when the rod is in the reference position can be fixed to one side. With this configuration, the element used at the steering angle neutral position is always fixed to the element close to the magnet. Therefore, particularly, the fluctuation in measurement at the steering angle neutral position is eliminated and the stability of the steering drive is enhanced.

[0019] (Characteristic configuration) In the rear-wheel steering device according to the present invention, a temperature detection device is provided outside the housing, and the control unit stores the magnetic field strength value of the magnet in the reference position. When the detected temperature by the temperature detection device is within a predetermined range, the magnetic field strength value can be corrected according to the detected temperature and the position of the rod can be adjusted.

[0020] (Effect) The rod provided with the magnet may expand and contract according to the ambient temperature. For example, when the rod thermally expands at high temperature, the position of the magnet is displaced from the reference position. Since the rod is the main shaft of the rear-wheel steering device of the vehicle, if the position of the magnet is set based on the magnetic field strength value stored in the control unit, the position of the rod is displaced from the actual steering angle neutral position, which gives the driver a sense of discomfort.

[0021] With this configuration, by providing a temperature detection device, it has a function of correcting the reference position of the magnet. That is, the amount of expansion and contraction of the rod is calculated from the difference between the magnetic field strength value stored in the control unit and the detected temperature value at each time, and the reference position of the rod is optimized.

[0022] In particular, in this configuration, when the magnet is in the neutral position, each element can detect the position of the magnet, and the correction accuracy can be improved by amplifying the difference in the detected values ​​from each element. [Brief explanation of the drawing]

[0023] [Figure 1] Cross-sectional view showing the configuration of the rear wheel steering system according to the first embodiment. [Figure 2] Cross-sectional view showing the drive unit of the rear wheel steering system according to the first embodiment. [Figure 3] Cross-sectional view showing the position detection unit of the rear wheel steering device according to the first embodiment. [Figure 4] A perspective view showing details of the position detection unit according to the first embodiment. [Figure 5] Explanatory diagram showing the position detection method according to the first embodiment. [Figure 6] An explanatory diagram showing an example of the arrangement of magnets according to the first embodiment. [Figure 7] Flowchart showing the position detection method according to the first embodiment [Modes for carrying out the invention]

[0024] [First Embodiment] (overview) Figure 1 shows, for example, a rear-wheel steering device A according to the present invention. In the rear-wheel steering device A, for example, a cylindrical nut 2 is rotationally driven by an electric motor 1, which is a drive unit M, causing a rod 3, which is screwed into the nut 2, to reciprocate. A sliding surface is formed on a part of the rod 3 that abuts against the inner surface of the housing 4 of the rear-wheel steering device A, and the rod 3 is configured to reciprocate without rotating.

[0025] Figures 1 and 2 show the configuration of the rear-wheel steering device A according to this embodiment. The rear-wheel steering device A comprises a control unit C located on the left side of Figure 1 and a drive unit M located on the right side. The control unit C has a pair of elements 25 that measure the displacement state of the rod 3, and calculates the position of the rod 3 based on signals from these elements 25. Based on the calculation result, the control unit C supplies a drive signal to the drive unit M to move the rod 3 to the desired position.

[0026] (Drive unit) As shown in Figure 2, the drive unit M of this embodiment includes a stator 5 having an axis X aligned with the direction of movement of the rear wheel steering device A, and a cylindrical rotor 6 that rotates inside it. A rod 3 is inserted through the inside of the cylindrical rotor 6. The rotor 6 is supported on both sides by rotor bearings 7 on the housing 4, on both outer sides along the axis X, with the opposing position of the stator 5 in between.

[0027] (Planetary gear mechanism) A planetary gear mechanism P is connected to one end of the rotor 6. Specifically, a sun gear P1 is formed on the outer surface of the end of the rotor 6. Three planetary gears P2 mesh with the sun gear P1, and a ring gear P3 fixed to the housing 4 meshes with the outside of the planetary gears P2.

[0028] The carrier K of the planetary gear P2 is screwed and fixed to the outer circumference of the nut 2 that engages with the rod 3. The carrier K has a first carrier K1 fixed to the outer surface of the nut 2, and a second carrier K2 that is fitted and fixed to the outside of the first carrier K1. Three shaft members 8, each supporting one of the three planetary gears P2, are fixed to the second carrier K2.

[0029] Nut 2 is cylindrical, and a female trapezoidal screw 9a, which serves as the output gear 9 of the drive unit M, is formed on its inner surface. On the other hand, a male trapezoidal screw 10a, which serves as the threaded portion 10, is formed on the outer surface of rod 3. Nut 2 is made of brass to provide wear resistance. Rod 3 reciprocates without rotating relative to housing 4 by bringing the sliding contact member 21, described later, into contact with the inner surface of housing 4. A bearing portion 11 using a thrust bearing is fitted onto the outer surface of nut 2, and this bearing portion 11 is fitted into the inner surface of housing 4.

[0030] The first carrier K1 is externally fitted to one end of the nut 2 and screwed in via the fixing screw portion 12. The other end of the nut 2 has a radially protruding bulge 2a, and the inner member 11a of the bearing portion 11 is clamped along the axis X direction by this bulge 2a and the end face of the first carrier K1. With this configuration, fixing the bearing portion 11 and the first carrier K1 to the nut 2 is simplified, and the assembly work can be made more efficient.

[0031] Further outward from the first carrier K1, the second carrier K2, which holds the planetary gear P2, is fitted and fixed. This fitting and fixing is performed using two types of fitting parts. One is a cylindrical first fitting part Ka formed on the inner side of the fitting direction along the axis X when viewed from the side of the second carrier K2. This is formed by a cylindrical fitting outer surface formed on the outer surface of the first carrier K1 and a cylindrical fitting inner surface formed on the inner surface of the second carrier K2. The other is a spline-shaped second fitting part Kb that is on the front side of the fitting direction when viewed from the side of the second carrier K2 and adjacent to the first fitting part Ka.

[0032] The second fitting portion Kb is configured, for example, with a star shape in cross-section perpendicular to the axis X. This prevents the first carrier K1 and the second carrier K2 from rotating relative to each other, resulting in a durable carrier K. Furthermore, when screwing the first carrier K1 into the nut 2, the second fitting portion Kb can be used as the engagement part of the fastening tool. In addition, the first carrier K1 and the second carrier K2 are made of steel instead of conventional brass to reduce weight and cost.

[0033] In this embodiment, the housing 4 has a particularly narrow shape, and the bearing portion 11 needs to be positioned deep inside the carrier K. Therefore, the installation sequence is as follows: the bearing portion 11 is attached to the nut 2, the bearing portion 11 is clamped by the first carrier K1, and then these are fixed to the housing 4. The second carrier K2 is attached to the first carrier K1 afterwards.

[0034] To fix the bearing portion 11, an annular spacer 13 that abuts against the outer member 11b of the bearing portion 11 and a retaining ring 14 that abuts against the spacer 13 to maintain the positions of the bearing portion 11 and the spacer 13 are used. The retaining ring 14 is, for example, a C-shaped snap ring that fits into a groove 15 formed on the inner surface of the housing 4.

[0035] After the bearing section 11 is fixed, the second carrier K2 is fitted and fixed to the first carrier K1. The order in which the planetary gear P2 is attached to the second carrier K2 can be either before or after the attachment of the second carrier K2 to the first carrier K1. The ring gear P3 is fitted to the inner surface of the housing 4 as shown in Figure 2.

[0036] (Displacement detection unit) As shown in Figures 3 and 4, the displacement detection unit S is formed by the magnet 24 and the detection element 25. Only one magnet 24 is provided on the surface of the rod 3. In contrast, two elements 25 are provided on the control board 26 along the direction of movement of the magnet 24.

[0037] (magnet) The magnet 24 is, for example, rod-shaped and is attached to the surface of the rod 3 using a slider 20, a sliding contact member 21, and a magnet block 24a. In this embodiment, the magnet 24 has a rotation-restricting effect so that the rod 3 does not rotate relative to the housing 4.

[0038] As shown in Figure 4, the slider 20 is a member having a U-shaped cross-section perpendicular to the axis X. The slider 20 is fixed to the rod 3 by mounting bolts, which are fastening members 23, through mounting holes 20b provided in the bottom portion 20a that forms the U-shape. The installation procedure involves inserting the rod 3 into the housing 4 and aligning the slider mounting position of the rod 3 with the positions of mutually opposing guide surfaces (not shown) formed in the opening of the housing 4. In this state, the slider 20, with the sliding contact member 21 already attached, is positioned and fastened with the fastening member 23.

[0039] A sliding contact member 21 is attached to the slider 20. The sliding contact member 21 slides against a guide surface (not shown) provided on the housing 4 during the reciprocating movement of the rod 3.

[0040] The sliding contact member 21 is attached to the slider 20 by inserting the groove-shaped insertion portion 21a formed on the sliding contact member 21 into a pair of protruding portions 20c that form a U shape on the slider 20. The inner wall 21b of the sliding contact member 21 that forms the insertion portion 21a has a claw portion formed as an engaging portion 21c, and the claw portion engages with the hole provided as an engaged portion 20d on the pair of protruding portions 20c. By performing this so-called snap-fit ​​engagement, the work of attaching the sliding contact member 21 to the slider 20 is simplified and the work cost can be reduced.

[0041] The slider 20 is made of a metal material such as steel or stainless steel, and can reliably receive the anti-rotation torque of the rod 3 that is received as a reaction force from the guide surface when the rod 3 moves back and forth. On the other hand, the sliding contact member 21 is made of a material having a low coefficient of friction, such as fluororesin.

[0042] Furthermore, the outward-facing surface of each of the pair of sliding contact members 21 becomes the sliding contact surface 21d, which slides against the guide surface of the housing 4 and prevents the rotation of the rod 3. To ensure that this rotation prevention is reliable, the outward-facing surfaces of the pair of protruding portions 20c of the slider 20 are formed as flat receiving surfaces 20f, which make surface contact with the inner wall 21b formed on the inside of the insertion portion 21a of the sliding contact member 21. By bringing these receiving surfaces 20f into contact with the inner wall 21b, the rotation restriction function of the rod 3 is reliably performed, enabling a higher torque for the rear wheel steering device A.

[0043] As shown in Figures 3 and 4, the magnet 24 is made of a long shape and is formed as an insert from a resin material to form a magnet block 24a. In this embodiment, even if the length of the magnet 24 is made short, two elements 25 are provided on either side of the magnet 24, so a wide detection range can be obtained. However, it is advantageous to increase the length of the magnet 24 so as to further widen the detection range. The magnet block 24a is fixed to the rod 3, but is installed in such a way that an external force that prevents the rotation of the rod 3 is not input to the magnet 24 from the sliding contact member 21.

[0044] Specifically, as shown in Figure 4, the magnet block 24a is inserted between a pair of sliding contact members 21, and the back surface of the magnet block 24a is positioned to contact two first receiving seats 20g formed on the bottom 20a of the slider 20. This ensures that the sensing surface of the magnet 24 is positioned at a predetermined height relative to the surface of the rod 3.

[0045] Furthermore, mounting holes are provided near both ends of the magnet block 24a in the direction along the axis X. Fixing screws are inserted through these mounting holes and screwed into the female threads provided on the rod 3 to fix the magnet block 24. Although not shown in the illustration, a separate locking mechanism or the like may be provided between the magnet block 24a and the sliding contact member 21 for further fixation.

[0046] In this way, after fixing the slider 20 and the sliding contact member 21 to the rod 3 inserted through the housing 4, the magnet block 24a can be positioned relative to the sliding contact member 21, allowing the magnet 24 to be easily installed on the rod 3.

[0047] With this configuration, no force acts from the sliding contact member 21 to the magnet 24 to prevent the rod 3 from rotating during its reciprocating movement. Therefore, the risk of damage to the magnet 24 is eliminated, and a displacement detection unit S with a rational structure and increased durability can be obtained.

[0048] (element) The position of rod 3 is detected by two elements 25 provided on the substrate that constitutes the control unit C.

[0049] As shown in Figure 3, a control board 26 of the control unit C is positioned facing downwards above the magnet 24, and two elements 25 are provided on it. The control unit C calculates the position of the magnet 24 based on the signals obtained from the elements 25 and transmits a drive signal to the drive unit M to move the rod 3 to the desired position.

[0050] Figures 5 to 7 show how the position of rod 3 is calculated. Figure 5 shows how element 25 detects the magnetic field strength from magnet 24.

[0051] Figure 5(a) shows the magnetic field generated by the magnet 24 as detected by the element 25. The element 25 used in this embodiment can detect a first directional magnetic field Bx along the direction of movement of the magnet 24, and a second directional magnetic field Bz perpendicular to the direction of movement and along the plane containing the two elements 25 and the magnet 24. Incidentally, the third directional magnetic field By, which is perpendicular to these, is omitted because it is weak.

[0052] Figure 5(b) shows the magnetic field detection results of element 25 according to the position of magnet 24. When magnet 24 is moved relative to element 25 placed in the center position, the long dashed line in the figure shows the detection result of the first direction magnetic field Bx, and the short dashed line shows the detection result of the second direction magnetic field Bz. These first direction magnetic field Bx and second direction magnetic field Bz are detected as a combined magnetic field B using the combination formula shown in Figure 5(a).

[0053] In the equation, α represents the lower detection limit of the magnetic field that element 25 can detect. Setting a higher lower detection limit improves the position detection accuracy of the magnet 24. However, the displacement measurement range of the magnet 24 becomes shorter. On the other hand, lowering the lower detection limit widens the displacement measurement range of the magnet 24, but the position detection accuracy decreases because the detected value of element 25 becomes smaller.

[0054] In this embodiment, for example, as shown in Figure 5(b), the detection value α when the magnet 24 is directly below one element 25 is used as the lower detection limit. As a result, a detection value can be reliably obtained in the region shown by the thick solid line in the combined magnetic field B shown in Figure 5(b). In this case, even if the magnet 24 and the element 25 do not overlap in a direction perpendicular to the direction of movement of the magnet 24, accurate position detection of the magnet 24 is possible, and a wide detection range L can be secured for detecting the position of the magnet 24.

[0055] As a result, the length of the magnet 24 is set to be shorter than that of conventional magnets. For example, when the distance between the furthest ends of a pair of elements 25, namely the end of the first element 251 and the end of the second element 252, is defined as the distance between the elements, the length of the magnet 24 along the axis X is configured to be shorter than the distance between the elements.

[0056] The magnetic field detection range of the magnet 24, provided by a single element 25, is formed on both sides of the element 25 along the axis X. In other words, for a pair of elements 251 and 252 positioned at a predetermined location, the magnet 24 can be displaced not only between the two elements 251 and 252, but also further outward from one of the elements 25. Therefore, even when using only one magnet 24, the magnetic field detection range can be expanded by using two elements 251 and 252.

[0057] Figure 5(c) shows the combined state of the first combined magnetic field B1 detected by the first element 251 and the second combined magnetic field B2 detected by the second element 252. This makes it possible to obtain a combined detection range 2L in which the length of the position detection range of the magnet 24 is approximately twice the length of the detection range L mentioned above.

[0058] As described above, this configuration includes a pair of elements 251 and 252 that are dispersed along the axis X and are positioned such that the ranges for detecting the strength of the magnetic field formed by the magnet 24 overlap, and a control unit C that calculates the position of the magnet 24 along the axis X relative to the pair of elements 251 and 252 from the detection result of at least one of the elements 25 of the pair 251 and 252.

[0059] This allows multiple elements 25 to be placed on the magnet 24, and the elements 25 that detect the magnetic field of the magnet 24 to be sequentially replaced as the magnet 24 moves back and forth.

[0060] The extent to which the length of the magnet 24 can be shortened relative to the distance between a pair of elements 251 and 252 can be set to a length that does not overlap simultaneously in the direction perpendicular to the axis X when the magnet 24 is positioned between the pair of elements 251 and 252. The shortest length of the magnet 24 is appropriately determined based on the magnetic field strength formed by the magnet 24 and the magnetic field detection range of the pair of elements 251 and 252.

[0061] When the shortest length of the magnet 24 is determined, the movable range in which the position of the magnet 24 can be detected is determined. That is, even outside the first element 251 and outside the second element 252, the positions of the magnet 24 that can be detected by the respective elements 25 are determined, so the region between both positions becomes the movable range of the magnet 24.

[0062] By providing a plurality of elements 25 in this way, it is possible to widen the position detection range of the magnet 24 while maintaining the small size of the magnet 24. If the size of the magnet 24 is maintained compactly, it is difficult for inconveniences such as the magnet 24 interfering with other objects during the reciprocating operation of the rod 3 to which the magnet 24 is attached, and it becomes easy to increase the reciprocating stroke of the rod 3.

[0063] With this configuration, it is possible to increase the rear wheel steering angle while maintaining the compactness of the device dimensions, and a low-cost rear wheel steering device A with excellent mounting performance can be obtained.

[0064] (Reference position of magnet) As shown in FIG. 6, when the rod 3 is in the reference position with respect to the housing 4, the position of the magnet 24 along the axis X is set to be different from the central position CL between the pair of elements 25 in the same direction.

[0065] For the position detection of the magnet 24, the element 25 on the side where the distance from the center position of the magnet 24 to each element 25 is close, that is, the element 25 with a high detected value of magnetic field strength, is used. Here, as the initial position of the magnet 24, the distance from the first element 251 is a', and the distance from the second element 252 is b', and it is set so that a' < b'.

[0066] In this way, by varying the distance between the magnet 24 and each element 25 at the reference position of the rod 3, the element 25 used when the rod 3 is in the reference position can be fixed to the closer side. With the rear-wheel steering device A of this configuration, the element 25 used at the steering angle neutral position is always fixed to the element 25 closest to the magnet 24. Therefore, for example, when the vehicle's IG switch is turned ON and the calculations of the displacement detection unit S and the control unit C begin, fluctuations in whether the position of the magnet 24 is determined based on the measured value of the first element 251 or the second element 252 are eliminated, and the stability of the steering drive is increased.

[0067] As shown in Figure 1, in the rear-wheel steering device A of this embodiment, for example, a temperature detection device T is provided on the outside near one end of the housing 4. Various types of thermocouples can be used as the temperature detection device T. The temperature of the rod 3 is measured by this, and the control unit C calculates the dimensional change of the rod 3. Since the rod 3 is a movable member, the thermocouple does not necessarily need to be in contact with the rod 3. In Figure 1, the thermocouple is provided in the part of the housing 4 that slides and supports the rod 3.

[0068] The control unit C stores the magnetic field strength value of the magnet 24 at the reference position, and when the temperature detected by the temperature detection device T is within a predetermined range, the magnetic field strength value is corrected according to the detected temperature and the position of the rod 3 is adjusted.

[0069] The specific correction method will be explained using the flowcharts in Figures 6 and 7. When the vehicle's ignition switch is turned ON (#10), the control unit C calculates a first distance a' based on the detected value of the first element 251 and a second distance b' based on the detected value of the second element 252. The control unit C then determines whether the sum of these first distance a' and second distance b' is equal to the sum of the initial first distance a and initial second distance b stored in its memory (#20).

[0070] If the total distance remains unchanged at this point, the system proceeds to the next step, #30. On the other hand, if there is an error in the total distance, an abnormality is detected (#50) indicating a problem somewhere in the system, and a warning is displayed on the instrument panel, for example.

[0071] In step #30, it is determined whether the initial first distance a and the initial first distance a' are equal, and whether the initial second distance b and the initial second distance b' are equal (#30). In Figure 6, the initial first distance a and the initial second distance b are shown to be equal, but in this embodiment, the initial first distance a and the initial second distance b are different from the beginning, and it is assumed that the initial first distance a and the initial distance a' are equal, and the initial second distance b and the initial second distance b' are equal. If it is determined that this condition is met, it is determined that the position of the magnet 24, i.e., the position of the rod 3, is at the reference position, and normal startup (#40) ends.

[0072] On the other hand, if the judgment condition in step #30 is not met, the control unit C checks the output of the temperature detection device T (#60). This is because the reason why the magnet 24, which should be in its initial position, is misaligned is thought to be due to the expansion and contraction of the rod 3 due to temperature changes. Here, two cases are considered in particular: when the temperature of the rod 3 is high and when it is low. For high-temperature conditions, the temperature is set appropriately by considering, for example, the heating conditions associated with the sliding of the rod 3 and the housing 4, and the heat transfer from the exhaust muffler. On the other hand, for low-temperature conditions, the temperature is set appropriately by considering, for example, the temperature range of the operating environment. Specifically, this would be in the range of several tens of degrees Celsius to about 100 degrees Celsius.

[0073] If the temperature condition is included in the judgment value in step #60, the process proceeds to step #70, where the control unit C starts a correction calculation. This allows the correction amount related to the position adjustment of rod 3 to be confirmed using a correction amount map based on the detected temperature (#80). This correction amount is determined from the correlation between the difference between the first distance a' and the second distance b' corresponding to the detected temperature, which is stored as a map by the control unit C, and the motor is driven to correct the initial first distance a and initial second distance b for the position of rod 3 (#90). Note that this temperature correction is performed only when the ignition switch is turned on.

[0074] As in this configuration, by including a temperature detection device T, the reference position of the magnet 24 can be corrected as needed. In other words, the amount of extension and contraction of the rod 3 is calculated from the difference between the magnetic field strength value stored in the control unit C and the temperature detection value at the time of measurement, and the reference position of the rod 3 is optimized, so that the steering state of the rear wheels can always be optimized.

[0075] As described above, in the rear-wheel steering device A having one magnet 24 and two elements 25, the elements 25 that detect the magnetic field of the magnet 24 can be sequentially replaced as the magnet 24 moves back and forth. The magnetic field detection range of one element 25 is determined by the size of the magnet 24 and the strength of the magnetic field, but the magnetic field detection range of the magnet 24 is increased by overlapping the magnetic field detection ranges of a pair of elements 25.

[0076] As a result, the position detection range can be expanded while keeping the dimensions of the magnet 24 small. If the magnet 24 is compact, the ease of mounting to the rod 3 is improved, interference between the rod 3 and other objects is eliminated, and a rational displacement detection unit S can be obtained. With such a configuration, a rear-wheel steering device A with excellent mountability can be easily obtained. [Industrial applicability]

[0077] The rear-wheel steering device of the present invention can be widely applied to devices that have a configuration in which a rod is reciprocated by a drive unit, and magnets and elements are distributed between the rod and the housing as they move relative to each other, thereby enabling measurement of the rod's displacement. [Explanation of symbols]

[0078] 24 Magnets 25 3 rods 4 Housing A. Rear-wheel steering system C control section M Drive Unit S Displacement detection unit T Temperature detection device X-axis

Claims

1. In the housing, The drive unit and The aforementioned drive unit provides a rod that moves back and forth along its own axis in a non-rotating state, The system includes a displacement detection unit for detecting the displacement of the aforementioned rod, The displacement detection unit, A magnet fixed to the rod and moving back and forth together with the rod, A pair of elements are dispersed along the axis and arranged such that the ranges for detecting the strength of the magnetic field formed by the magnet overlap, The system includes a control unit that calculates the position of the magnet along the axis of the pair of elements from the detection result of at least one of the pair of elements, A rear-wheel steering device in which, when the distance between the ends of one of the pair of elements and the end of the other of the pair of elements in the furthest possible combination is defined as the distance between the ends, the length of the magnet along the axis is configured to be shorter than the distance between the elements.

2. The rear wheel steering device according to claim 1, wherein the length of the magnet is set such that, when the magnet is positioned between the pair of elements, the magnet and the pair of elements do not overlap simultaneously in a direction perpendicular to the axis.

3. The rear wheel steering device according to claim 1, wherein, when the rod is in a reference position relative to the housing, the position of the magnet along the axis is set to be different from the central position of the pair of elements in the same direction.

4. A temperature detection device is provided on the outside of the housing, The control unit stores the magnetic field strength value of the magnet at the reference position. The rear wheel steering device according to claim 3, wherein when the temperature detected by the temperature detection device is within a predetermined range, the magnetic field strength value is corrected according to the detected temperature and the position of the rod is adjusted.

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