JP5169704B2 - Vehicle steering system - Google Patents

Description

  The present invention relates to a vehicle steering system including a steering assist device that has a drive source and generates an assisting force for assisting wheel steering, and more particularly to control of the assisting force.

As a vehicle steering system, there is a so-called power steering system that includes a steering assist device that assists the steering of a wheel by relying on a force generated by a drive source. In the power steering system, an assisting force, which is a force assisting wheel steering, is generally controlled based on a steering force applied to a steering operation member operated by a driver. For example, in order to reduce the load on the driving source, the system described in Patent Document 1 below is configured to perform control for suppressing the assisting force. Specifically, when the current flowing through the electromagnetic motor that is the drive source is detected and the average value of the current exceeds a specified value, the change gradient of the assisting force with respect to the increase in the steering force is expressed as the average value of the current. Accordingly, the assisting force is configured to be suppressed by gradually reducing the size from the normal value.
JP-A-8-133108

  However, in the system described in Patent Document 1, even if the change gradient of the assisting force with respect to the steering force is changed in order to suppress the assisting force, the assisting force does not always increase as the steering force increases. When the control is changed to control the force, if there is a gap in the assisting force generated by the steering assisting device, the driver's steering feeling changes suddenly. That is, in the power steering system, when switching from the normal control to the control that suppresses the assisting force, it is considered that the practicality of the system is improved by suppressing the change in the steering feeling of the driver. This invention is made | formed in view of such a situation, and makes it a subject to improve the practicality of the vehicle steering system provided with the steering assistance apparatus.

In order to solve the above-described problems, the vehicle steering system according to the present invention has (a) a standard assisting force defined such that the assisting force generated by the steering assisting device increases as the steering force increases. And (b) when the steering speed of the steering operation member is greater than or equal to the threshold speed in the process of increasing the steering force, or (ii) steering operation When the steering amount of the member is equal to or greater than the threshold steering amount, the first setting condition is satisfied, and instead of the standard control, the assisting force is the steering force at the time when the first setting condition is satisfied. Auxiliary force suppression control that controls the drive source can be executed so that the standard assisting force corresponding to the hour steering force increases as the steering force increases and becomes a restraining assisting force that is defined to be smaller than the standard assisting force. Configured.

  In the vehicle steering system of the present invention, the assisting force suppression control, which is relatively simple control, reduces the assisting force generated by the steering assisting device to be smaller than the assisting force generated in the standard control that is normally performed. It is possible to reliably increase the assisting force at the start of the control according to the increase of the control, to prevent a sudden change in the assisting force and to suppress a change in the steering feeling of the driver. By having such advantages, the vehicle steering system of the present invention becomes highly practical.

Aspects of the Invention

  In the following, some aspects of the invention that can be claimed in the present application (hereinafter sometimes referred to as “claimable invention”) will be exemplified and described. As with the claims, each aspect is divided into sections, each section is numbered, and is described in a form that cites the numbers of other sections as necessary. This is merely for the purpose of facilitating the understanding of the claimable inventions, and is not intended to limit the combinations of the constituent elements constituting those inventions to those described in the following sections. In other words, the claimable invention should be construed in consideration of the description accompanying each section, the description of the embodiments, etc., and as long as the interpretation is followed, another aspect is added to the form of each section. In addition, an aspect in which some constituent elements are deleted from the aspect of each item can be an aspect of the claimable invention.

In each of the following items, the combination of items (1) and (9) corresponds to claim 1, and the technical feature of item (11) is added to claim 1 in claim 2. Equivalent to. Further, the combination of the items (1) and (11) corresponds to claim 3, and any one of claims 1 to 3 with the technical feature of (2) added. The technical feature of item (3) added to item 4 is added to item 4, the method of item (5) and item (6) is added to any one of items 1 to 5. The characteristic features added correspond to claim 6 respectively.

(1) a steering operation member operated by a driver;
A steering device for turning the wheels so that the steering amount is in accordance with the steering amount of the steering operation member;
A steering force transmission mechanism that transmits a steering force applied to the steering operation member to the steering device;
A steering assist device that has a drive source and generates an assist force for assisting the steering of the wheel based on the force generated by the drive source;
And a control device that controls the drive source of the steering assist device and controls the assist force generated by the steering assist device based on the steering force of the steering operation member. And
The control device is
A standard control unit that executes standard control for controlling the drive source so that the assisting force generated by the steering assisting device is a standard assisting force that is defined to increase with an increase in steering force;
When the first setting condition is satisfied in the process of increasing the steering force, instead of the standard control, the steering force generated by the steering assist device at the time when the first setting condition is satisfied The drive source is adjusted so that the standard assisting force corresponding to the steering force when the condition is satisfied increases as the steering force increases and becomes a restraining assisting force defined to be smaller than the standard assisting force. A vehicle steering system comprising: an assisting force suppression control unit that executes an assisting force suppression control that controls the vehicle.

  In the aspect described in this section, it is necessary to suppress the increase in the assisting force generated by the steering assisting device, or the first setting condition that represents the situation where it is desirable to suppress the increase in the assisting force, When the steering force applied to the member (hereinafter, sometimes simply referred to as “operation member”) is satisfied in the process of increasing, the assisting force suppression control is executed instead of the standard control executed at the normal time. The The assisting force suppression control constantly increases the assisting force generated by the steering assisting device from the assisting force at the time when the condition is satisfied in accordance with the increase of the steering force, and the standard control for the same steering force. This is an aspect that is smaller than the assisting force. For example, when the steering force is on the horizontal axis and the assist force is on the vertical axis, the line segment drawn by the standard assist force in the standard control is defined as a standard characteristic line, and the line segment drawn by the suppress assist force in the assist force suppression control Is defined as a suppression characteristic line. In that case, in the aspect of this section, when the assisting force increases along the standard characteristic line according to the increase of the steering force and the first setting condition is satisfied, the standard characteristic at the time when the condition is satisfied From the point on the line, it increases following the suppression characteristic line that extends more gently than the standard characteristic line. In other words, according to the aspect of this section, when the control is switched from the standard control to the assisting force suppression control, the assisting force is prevented from changing suddenly or the steering feeling is prevented from changing suddenly. It is possible to suppress a sense of discomfort experienced by the driver due to the switchover to the power suppression control.

  As described above, the “first setting condition” described in this section can determine that it is necessary to suppress the increase of the assisting force, or that it is desirable to suppress the increase of the assisting force. There are no particular restrictions on the purpose of suppressing the assisting force, and various parameters can be used. For example, when the assist force is predicted to increase rapidly based on the change rate of the assist force, or based on the average value, total amount, etc. of the assist force (supply current, supply power) within the set time retroactive from the present time For example, when it is predicted that the load on the drive source is increased, it may be determined that the first setting condition is satisfied. As described above, if the first setting condition is set for the purpose of reducing the load on the driving source, power saving and downsizing of the driving source can be achieved by the assisting force suppression control. Further, as will be described in detail later, it is also possible to employ the steering speed, the steering amount, and the like of the operation member as parameters used for the first setting condition.

  Incidentally, the “steering amount” and the “steering amount” described in this section mean the amounts from the neutral position of the operation member and the steering device, respectively. In addition, the “steering amount in accordance with the steering amount” referred to in this section is such that the steering gear ratio, which is the ratio of the change amount of the steering amount and the change amount of the steering amount, becomes a fixed ratio. It is not limited. As will be described in detail later, the steering force transmission mechanism includes a function in which the steering gear ratio changes or is changed, and the steering amount changes according to the steering amount.

(2) The control device
Even if the first setting condition is no longer satisfied during the execution of the assisting force suppression control, the assisting force suppression control unit performs the assisting force suppression control until the second setting condition is satisfied. The vehicle steering system according to item (1), which is configured to be continuously executed.

  The mode described in this section is a mode in which the first setting condition is the start condition of the assisting force suppression control and the second setting condition is set as the control end condition. In other words, in the aspect of this section, when the first setting condition is satisfied in the process of increasing the steering force, the standard control is switched to the assisting force suppression control, and when the second setting condition is satisfied, the assisting force The control is returned from the suppression control to the standard control. Further, the aspect of this section is an aspect in which the assisting force increases or decreases on the above-described suppression characteristic line according to the increase or decrease of the steering force until the second setting condition is satisfied.

(3) The controller is
When the steering force decreases below the steering force when the condition is satisfied in the process of decreasing the steering force, the assisting force suppression control is switched to the standard control assuming that the second setting condition is satisfied. The vehicle steering system according to (2).

  To put it plainly, the mode described in this section is a mode in which the control is returned to the standard control when the above-described suppression characteristic line returns to the standard characteristic line in the process of decreasing the steering force. According to the aspect of this section, when the control is switched from the assisting force suppression control to the standard control, the assisting force is prevented from changing suddenly or the steering feeling is prevented from changing suddenly. It is possible to suppress a sense of incongruity experienced by the driver due to the switchover to the control.

(4) The controller is
When the assisting force to be generated by the steering assisting device exceeds a set force, the assisting force limiting unit that limits the assisting force generated by the steering assisting device to the set force (1) to (3) The vehicle steering system according to any one of the preceding claims.

  The mode described in this section can be a mode in which the setting force is determined in consideration of the upper limit value of the output of the drive source. In the aspect of this section, when the assist force reaches the set force, the driver's steering feeling changes suddenly. However, the assist force suppression control can make it difficult for the assist force to reach the set force. It is.

(5) The standard support force is
The vehicle steering system according to any one of items (1) to (4), wherein the gradient of the change with respect to the increase in the steering force is defined to gradually increase.

  The mode described in this section is a mode that embodies how to increase the assisting force in the standard control. The mode in which the assisting force changes on a downwardly convex curve, that is, the standard characteristics described above. This is an aspect in which the line becomes a downwardly convex curve. According to the aspect of this section, it is possible to prevent the driver from feeling that the steering is heavy.

(6) The suppression assisting force is
The vehicle steering system according to any one of (1) to (5), wherein a gradient of change with respect to an increase in the steering force is defined to be constant.

  The mode described in this section is a mode that embodies how to increase the assisting force in the assisting force suppression control. On the straight line passing through the point where the assisting force becomes the standard assisting force with respect to the steering force when the condition is satisfied. This is a mode in which the suppression characteristic line described above is a straight line. According to the aspect of this section, it is possible to determine the assisting force generated by the steering assisting device in the assisting force suppression control by simple calculation, and to reduce the calculation load in the assisting force suppression control unit. Is possible. Incidentally, for example, the aspect of this section may be an aspect in which the change gradient is the same regardless of the condition satisfying steering force. The larger the condition satisfying steering force, the larger the change gradient, or the condition satisfaction. The change gradient may be reduced as the hour steering force increases. The aspect of increasing the change gradient as the steering force when the condition is satisfied is an aspect in which emphasis is placed on assisting the steering of the wheel as the steering force when the condition is satisfied, and the change gradient is increased as the steering force when the condition is satisfied. The mode of reducing the value is a mode in which importance is placed on suppressing the assisting force as the steering force when the condition is satisfied is larger.

  If the aspect of this section is combined with the aspect in which the standard characteristic line described above becomes a downwardly convex curve, the difference between the standard characteristic line and the suppression characteristic line increases as the steering force increases. That is, as the steering force increases, the assisting force is largely suppressed.

(7) The steering force transmission mechanism is
The function of (1) to (6), wherein a steering gear ratio, which is a ratio of a change amount of the steering amount of the steering operation member and a change amount of the turning amount of the steering device, is changed or changed. The vehicle steering system according to any one of the above.

  The steering force transmission mechanism in this aspect may be, for example, a so-called VGRS (Variable Gear Ratio Steering) that has an actuator and can change the steering gear ratio by controlling the actuator. A structure having a structure to be described, or simply a structure having a mechanism such as a cam and the steering gear ratio mechanically changing according to the steering amount of the operation member may be used. In the steering force transmission mechanism according to the aspect of this section, when the quick steering gear ratio is used, that is, when the change amount of the turning amount with respect to the change amount of the steering amount is a large gear ratio, a small steering amount. Because it is necessary to make a large steering at, a large assisting force is required. Therefore, in the aspect of this section, it is easy to be in a situation where a large assisting force is generated, and the assisting force suppression control is particularly effective.

(8) The steering force transmission mechanism is
A first shaft having one end connected to one of the steering operation member and the steering device and rotatably disposed;
One end is connected to the other of the steering operation member and the steering device, and the rotation axis of the first shaft and the rotation axis of the first shaft are parallel to each other, and the rotation axis is rotatable by a predetermined distance. A second shaft disposed on
(A) at the other end of the first shaft, an engaging portion provided at a position away from the predetermined distance in the radial direction of the first shaft from the rotation axis of the first shaft; The other end of the two shafts is provided so as to extend in the radial direction of the second shaft, and engages with the engaging portion of the first shaft, and the engaging portion in the radial direction of the second shaft. And a guide passage that allows movement, and by rotating one of the first shaft and the second shaft, a rotation phase difference that is a difference between rotation phases of the first shaft and the second shaft is obtained. A rotation transmission mechanism configured to rotate while the other rotates,
The vehicle steering system according to (7), wherein the steering gear ratio has a function of changing according to a steering amount of the steering operation member.

  The aspect described in this section is an aspect in which the steering force transmission mechanism is limited to a structure in which the steering gear ratio changes according to the steering amount of the operation member. Since the “rotation transmission mechanism” described in this section changes the rotational phase difference between the two shafts, the difference between the rotation angle of the first shaft and the rotation angle of the second shaft changes. Specifically, for example, when one of the first shaft and the second shaft connected to the operation member is rotated from a position where there is no rotation angle difference (rotation phase difference) between the two shafts, Until the operation member side shaft rotates 180 °, the other of the first shaft and the second shaft connected to the steering device has a rotation angle smaller than the rotation angle of the operation member side shaft. When the shaft is rotated 180 °, the rotation angle of the shaft on the steering device side can be 180 °. That is, in the case of such a structure, the rotation angle difference between the two shafts increases from 0 and decreases from the middle until reaching 0, and the steering gear ratio is increased as the operating member side shaft rotates. It grows. According to the steering force transmission mechanism having such a structure, when the operation member is located near the neutral position, a gentle and stable handling is realized, and the response is improved as the steering amount of the operation member increases. Handling can be realized.

  In the aspect described in this section, since the steering force transmission mechanism has the above-described structure, the operable range of the operation member is relatively small (for example, the lock-to-lock is 360 °). ). As a result, the operation amount of the steering force transmission device, more specifically, the turning amount of the steering device with respect to the rotation angle of the shaft on the steering device side of the steering force transmission device becomes relatively large. That is, in the aspect of this paragraph, since it is necessary to make a large turning with a small steering amount, a large assisting force is required. Therefore, in the aspect of this section, it is easy to be in a situation where a large assisting force is generated, and the assisting force suppression control is more effective.

  (9) When the steering speed of the steering operation member is equal to or higher than a threshold speed, the control device causes the assisting force suppression control unit to execute the assisting force suppression control, assuming that the first setting condition is satisfied. The vehicle steering system according to any one of (1) to (8), configured as described above.

  (10) The control device according to (9), wherein the control device is configured to change the threshold speed to a smaller value when the steering force of the steering operation member is large than when the steering force is small. Vehicle steering system.

  The steering speed of the operation member is related to the steering force, and it is considered that the steering force increases as the steering speed increases. Therefore, the assisting force suppression control can be executed when it is estimated that the steering force is increased based on the steering speed as in the modes described in the above two items, which is effective. It is possible to suppress the assisting force. Note that, according to the latter aspect, the threshold speed can be changed to an appropriate magnitude according to the current steering force, so that the assisting force can be more effectively suppressed.

  (11) When the steering amount of the steering operation member is equal to or greater than a threshold steering amount, the control device executes the assisting force suppression control on the assisting force suppression control unit, assuming that the first setting condition is satisfied. The vehicle steering system according to any one of (1) to (10), wherein the steering system is configured to be

  In a vehicle steering system, a stopper is generally provided on an operation member or a steering device so as to limit steering or turning beyond a set amount. That is, in a steering system equipped with a steering assist device, the impact when hitting the stopper is relatively large. According to the aspect described in this section, it is possible to reduce the impact per stopper by suppressing the assisting force when it is likely to hit the stopper. In the aspect of this section, similarly to the threshold speed described above, the threshold steering amount can be changed to a smaller value when the steering force is large than when the steering force is small. It is.

  The first setting condition can be set based on both the steering amount of the operation member described in this section and the steering speed of the operation member described above. For example, the threshold steering amount can be changed to a smaller value when the steering speed is large than when the steering speed is small. Further, when the steering speed is equal to or higher than the threshold speed, it is determined that the first setting condition is satisfied, and the steering amount is equal to or higher than the threshold steering amount even if the steering speed is less than the threshold speed. It is also possible to adopt a mode in which it is determined that the first setting condition is satisfied.

  Hereinafter, embodiments of the claimable invention and modifications thereof will be described in detail with reference to the drawings. In addition to the following examples, the claimable invention is implemented in various modes including various modifications and improvements based on the knowledge of those skilled in the art, including the mode described in the above [Mode of Invention]. can do. Moreover, it is also possible to constitute the modification of the following Example using the technical matter described in the description of each item of [Aspect of the Invention].

<Overall configuration of vehicle steering system>
FIG. 1 shows the overall configuration of a vehicle steering system that is an embodiment of the claimable invention. The steering system includes a steering wheel 10 as a steering operation member operated by a driver, a steering column 12 that holds the steering wheel 10 at one end, a steering device 14 that steers a wheel, a steering column 12, An intermediate shaft (hereinafter sometimes abbreviated as “I / M shaft”) 16 positioned between the steering device 14 and the steering device 14 is configured. Furthermore, one end of the I / M shaft 16 and the output shaft 18 provided in the steering column 12 are connected by a universal joint 20, and the other end of the I / M shaft 16 and one end of the input shaft 22 provided in the steering device 14. The parts are connected by another universal joint 24.

  In FIG. 1, the system is arranged so that the right side, that is, the steering wheel 10 side faces the rear of the vehicle, and the left side, that is, the steering device 14 side faces the front of the vehicle. A portion of the I / M shaft 16 passing through the hole is covered with a boot 28 so as to pass through a hole provided in the dash panel 26 that partitions the engine chamber.

  The steered device 14 includes an input shaft 22, a housing 30 as an outer shell member, and a steered rod 32 for steering a wheel, and the steered rod 32 moves in the axial direction thereof. It is possible to be held by the housing 30 and to extend in the vehicle width direction. Both ends of the steered rod 32 are connected to a steering knuckle (not shown) that holds each of the left and right front wheels. The input shaft 22 is rotatably held by the housing 30 and is engaged with the steered rod 32 in the housing 30. A pinion (not shown) is formed at the end portion of the input shaft 22 on the vehicle front side, and a rack (not shown) formed at an intermediate portion in the axial direction of the steered rod 32 meshes with the pinion. The steered rod 32 and the input shaft 22 are engaged.

  The steering column 12 is fixedly supported on a part of the vehicle body by a steering support 36 provided in the instrument panel reinforcement 34. In the supported state, the steering column 12 is disposed in an inclined posture so that the front side of the vehicle is positioned downward as shown in the drawing. The steering column 12 is provided with a front bracket 38 at a front portion thereof, and a breakaway bracket (hereinafter sometimes abbreviated as “B.A.BKT”) 40 from the front bracket 38 to the vehicle rear side. Each of the front bracket 24 and the B.A.BKT 40 is attached to the steering support 22 so that the steering column 12 is supported at two locations. The supported steering column 12 has a rear portion protruding from the instrument panel 42 toward the vehicle rear side, and a steering wheel 10 is attached to the protruding rear end. A portion protruding from the instrument panel 42 of the steering column 12 is covered with a column cover 44, and a lower part is covered with an instrument panel lower cover 46.

  FIG. 2 shows a side sectional view of the steering column 12. The steering column 12 can be roughly divided into a column section 50 that holds the steering wheel 10 and can be expanded and contracted in the axial direction, and an EPS section 52 that is a main body that realizes an electric power steering function. These two sections 50 and 52 are integrated. Hereinafter, each of these sections will be described in order.

  The column section 50 includes a main shaft 54 that holds the steering wheel 10 at an end on the vehicle rear side, and a column tube 56 that serves as a housing that rotatably holds the main shaft 54 in a state where the main shaft 54 is inserted. ing. The main shaft 54 includes an upper shaft 58 positioned on the vehicle rear side, that is, on the upper side, and a lower shaft 60 positioned on the vehicle front side, that is, on the lower side. The upper shaft 58 is formed in a pipe shape and the lower shaft 60 is formed in a rod shape, and the rear portion of the lower shaft 60 is inserted into the front portion of the upper shaft 58. The upper shaft 58 and the lower shaft 60 are spline-fitted, and the upper shaft 58 and the lower shaft 60 are connected in a state in which they can be relatively moved in the rotation axis direction but cannot be relatively rotated. That is, the main shaft 54 has a structure that can be expanded and contracted in the rotation axis direction. The lower shaft 60 is composed of a shaft main body portion 62 on the rear side thereof and a circular flange portion 64 having an outer diameter larger than the outer diameter of the shaft main body portion 62 on the front side of the shaft main body portion 62. The circular flange portion 64 is connected to an EPS section 52 described later. In the steering column 12, the shaft main body 62 of the lower shaft 60 and the upper shaft 58 constitute a shaft main body of the main shaft 54.

  The column tube 56 includes an upper tube 66 positioned on the vehicle rear side (upper side) and a lower tube 68 positioned on the vehicle front side (lower side). The upper tube 66 and the lower tube 68 are both cylindrical, and the rear part of the lower tube 68 as the second cylinder member is fitted in the front part of the upper tube 66 as the first cylinder member. The lower tube 68 has a stepped shape, a small-diameter portion 70 having an outer diameter smaller than the inner diameter of the upper tube 66 in a rear portion thereof, and a large-diameter portion having an outer shape larger than the inner diameter of the upper tube 66 in a front portion thereof. 72, and a stepped portion 74 that connects the small diameter portion 70 and the large diameter portion 72. A liner (not shown) is provided between the small-diameter portion 70 of the lower tube 68 and the upper tube 66, and the lower tube 68 is inserted into the upper tube 66 without rattling through the liner. At the same time, the relative movement of the upper tube 66 and the lower tube 68 in the rotational axis direction is facilitated. That is, the column tube 56 has a structure that can be expanded and contracted in the rotation axis direction.

  A radial bearing 76 is disposed at the rear end portion of the upper tube 66, and a radial bearing 78 is disposed at a large diameter portion 72 of the lower tube 68 via a part of an EPS section 52 described later. Yes. The main shaft 54 is rotatably held by the bearings 76 and 78. With such a structure, the column section 50 can be expanded and contracted while ensuring the rotation of the main shaft 54.

  FIG. 3 shows a side cross-sectional view of the EPS section 52. The EPS section 52 includes an output shaft 18 for outputting a steering force applied to the steering wheel 10 to the steering device, and an electromagnetic motor 80 as a drive source. The motor 80 rotates the output shaft 18. A steering assist device 82 that assists the output (hereinafter may be simply referred to as “assistance device 82”) and an EPS housing 84 that rotatably holds the output shaft 18 and accommodates the assist device 82. ing. The output shaft 18 is configured by integrating an output side shaft 86, an input side shaft 88, and a torsion bar 90. The output side shaft 86 extends from the front side of the vehicle of the EPS housing 84 and is connected to the I / M shaft 16 via the universal joint 20 at the extended portion, and outputs rotation to the steering device 14. To do.

  The output side shaft 86 has a hollow structure, and the input side shaft 88 is inserted into a portion of the output side shaft 86 on the vehicle rear side. A bearing 92 is interposed between the inner peripheral surface of the output side shaft 86 and the outer peripheral surface of the input side shaft 88, and the output side shaft 86 and the input side shaft 88 can be rotated relative to each other. The input side shaft 88 has a bottomed hole that opens in an end surface on the vehicle front side and extends in the rotation axis direction. One end of the torsion bar 90 is fixed to the bottom of the bottomed hole by a pin 94, and the other end of the torsion bar 90 is a through hole that passes through the output shaft 86 in the rotation axis direction. It is fixed to the front end by a pin 96. With such a configuration, the output shaft 18 allows the torsion bar 90 to be twisted, and is itself twisted accordingly. Further, the output side shaft 86 is rotatably held by the EPS housing 84 via two radial bearings 98 and 100 on the outer periphery thereof, and the input side shaft 88 is attached to the EPS housing 84 via the needle bearing 102 on the outer periphery thereof. It is held rotatably.

  The assisting device 82 includes the electromagnetic motor 80, a worm 104 connected to the motor shaft of the electromagnetic motor 80, and a worm wheel 106 engaged with the worm 104. The worm wheel 106 is fixed to the output side shaft 86 of the output shaft 18 and cannot be rotated relative to the output side shaft 86. With such a structure, a rotational force is applied to the worm 104 by the electromagnetic motor 80 and a rotational force is applied to the worm wheel 106. That is, the assisting device 82 has a structure in which the rotational output of the output shaft 18 is assisted by the electromagnetic motor 80 to generate an assisting force for assisting the wheel steering.

  The EPS section 52 includes a relative displacement amount sensor 108 for detecting a steering force. The relative displacement sensor 108 is provided between an output side shaft 86 to which the vehicle front portion of the torsion bar 90 is fixed and an input side shaft 88 to which the vehicle rear portion of the torsion bar 90 is fixed. The relative rotational displacement amount between the output side shaft 86 and the input side shaft 88 is detected. The steering force (steering torque) can be estimated based on the relative rotational displacement, and the operation of the electromagnetic motor 80 is controlled so as to generate an assisting force corresponding to the magnitude of the steering force. .

  The output shaft 18 is disposed in a state where the rotation axis of the main shaft 54 and the axis of the output shaft 18 are parallel to each other, and the rotation axes are shifted by a predetermined amount. It is connected to the part. Specifically, first, the lower shaft 60 constituting the main shaft 54 has a circular flange on the front end surface of the circular flange portion 64 as shown in FIG. 4 which is a cross-sectional view taken along the line AA ′ of FIG. A groove 114 extending in the radial direction of the portion 64 is formed. On the other hand, an annular ring plate 116 is fixedly fitted to the input side shaft 88 at the end on the rear side thereof. The end surface on the rear side of the annular plate 116 and the end surface on the front side of the circular flange portion 64 of the lower shaft 60 face each other with a small gap. And pin 118 is being fixed to annular plate 116 in the state where it protrudes to the vehicles back side. A cylindrical roller 122 is provided on the protruding portion of the pin 118 via a needle bearing 120. The outer diameter of the roller 122 is slightly smaller than the width of the groove 114. When the roller 122 is engaged with the groove 114, the input side shaft 88, that is, the output shaft 18 is connected to the lower shaft 60 constituting the main shaft 54.

  That is, in the steering column 12, the pin 118, the needle bearing 120, and the roller 122 constitute a protruding portion that protrudes from the annular plate 116 in the direction in which the rotation axis of the input side shaft 88 extends. The output shaft 18 and the annular plate 116 constitute a steering device side shaft as a first shaft. The shaft main body portion of the steering device side shaft is constituted by an input side shaft 88 and an output side shaft 86. Incidentally, the main shaft 54 as the operation member side shaft functions as a second shaft.

  When the steering wheel 10 is rotated by the driver, the main shaft 54 rotates about its own rotation axis. At that time, the roller 122 engaged with the groove 114 formed in the circular flange portion 64 of the lower shaft 60 is restricted from being displaced in the circumferential direction by the pair of side wall surfaces 126 of the groove 114. At the same time, the groove 114 allows the shaft 60 to move in the radial direction. That is, the pair of side wall surfaces 126 functions as a pair of guide surfaces, and the groove 114 functions as a guide passage. When the roller 122 is moved in the groove 114 along with the rotation of the lower shaft 60, the rotational force of the lower shaft 60 is applied to the input side shaft 88 via the roller 122, the pin 118, the annular plate 116, and the like. Thus, the input shaft 88 rotates about its own rotation axis. That is, the steering column 12 includes a rotation transmission mechanism that transmits the rotation around the rotation axis of the lower shaft 60 to the input side shaft 88 arranged so that the rotation axis of the steering column 12 is shifted from the rotation axis of the lower shaft 60. It has been done. The rotation transmission mechanism includes a groove 114, a roller 122, a pin 118, a needle bearing 120, and the like. With the structure as described above, the steering column 12 transmits the steering force input to the steering wheel 10 to the steering device 18 via the I / M shaft 16 or the like. That is, a steering force transmission mechanism that includes the steering column 12 and the I / M shaft 16 and transmits the steering force of the steering wheel 10 to the steering device 18 is configured.

  The steering column 12 is attached to a part of the vehicle body at the front end portion of the EPS section 52 and the upper tube 66 of the column section 50. The EPS bracket 84 of the EPS section 52 is fixedly provided with the front bracket 38 described above, and the front bracket 38 is provided with a shaft insertion hole 130. A bearing member 134 having a shaft hole 132 is fixed to the steering support 36, and the support shaft 136 is inserted into the shaft insertion hole 130 of the front bracket 38 and the shaft hole 132 of the bearing member 134. Thus, the steering column 12 is supported so as to be swingable about the support shaft 136.

  On the other hand, the column section 50 is held by the B.A.BKT 40, and the B.A.BKT 40 is attached to the steering support 36. More specifically, as shown in FIG. 5, the B.A.BKT 40 includes a holding member 142 that holds the held member 140 fixed to the upper tube 66, and a steering support 36 that is fixed to the holding member 142. And a mounting plate 144 to be mounted, and is fastened to the steering support 36 using a slot 146 provided in the mounting plate 144. Long holes 148 and 150 are formed in the held member 140 and the holding member 142, respectively, and a rod 152 passes through them. Although not shown in the drawing, the holding member 142 is formed using the rod 152. The held member 140 is clamped. This clamping force prevents the upper tube 66 from being displaced. By operating the operation lever 154, it is possible to weaken the clamping force. When the clamping force is weakened, the movement along the elongated hole 148 of the rod 152 is allowed, so that the upper tube 66 is allowed to move in the axial direction with respect to the lower tube 68 together with the axial movement of the upper shaft 58 relative to the lower shaft 60, and the column section 50 is allowed to expand and contract. Further, since the movement of the rod 152 along the long hole 150 is allowed, the steering column 12 is allowed to swing around the support shaft 136 inserted through the front bracket 38. That is, the steering column 12 includes the tilt / telescopic mechanism 156 having such a structure.

  When the driver collides with the steering wheel 10 due to the collision of the vehicle, the B.A.BKT 40 is detached from the steering support 36 and the column section 50 is contracted. The steering column 12 is provided with an impact absorbing mechanism 157 that absorbs the impact of the secondary collision. The EA plate 158 is deformed as the steering column 56 contracts, so that the impact of the secondary collision is effective. To be absorbed.

  In the steering assist device 82 described above, the assist force is controlled by a steering electronic control unit 180 (hereinafter also referred to as “ECU 180”) shown in FIG. The ECU 180 is connected to an inverter 182 that is a drive circuit of the motor 80 of the steering assist device 82, and controls the motor 80 by controlling the inverter 182. The inverter 182 is connected to a power supply (not shown), and power (current) is supplied to the motor 80 from the power supply. Then, the supply current is performed by the inverter 182 changing the ratio (duty ratio) between the pulse on time and the pulse off time by PWM (Pulse Width Modulation).

  In addition, the ECU 180 detects the operation angle based on the relative position sensor [θ] 108 for estimating the steering torque and the neutral position of the steering wheel 20 as the steering amount of the operation member. Various sensors such as a sensor [δ] 184 are connected. The ECU 180 controls the operation of the steering assist device 82 based on signals from these sensors. Further, the ROM provided in the computer of the ECU 180 stores a program related to the control of the steering assist device 82, various data, and the like.

<Function of rotation transmission mechanism>
In the steering column 12, the output shaft 18 as the first shaft and the main shaft 54 as the second shaft, which are disposed in a state where the axes of the steering column 12 are shifted in parallel, more specifically, the input side of the output shaft 18. The shaft 88 and the lower shaft 60 of the main shaft 54 are connected by the rotation transmission mechanism. Therefore, the rotational phase of the lower shaft 60 and the rotational phase of the input side shaft 88 are shifted, and the rotational phase difference that is the difference between the rotational phases of the two shafts 60 and 88 is changed. This will be specifically described with reference to the drawings.

  6 is a cross-sectional view of a circular flange portion 64 of the lower shaft 60, an input side shaft 88 connected to the circular flange portion 64, and a roller 122 that engages with a groove 114 formed in the circular flange portion 64. 3 corresponds to the AA ′ sectional view of FIG. FIG. 6A shows a position corresponding to the steering neutral position of the wheel, that is, a state when the steering wheel 10 is in the neutral operation position. FIG. 6B shows a state where the steering wheel 10 is rotated counterclockwise from the neutral operation position. FIG. 6C shows a state when the steering wheel 10 is rotated 90 degrees in the clockwise direction from the neutral operation position. FIG. 6D shows a state when the steering wheel 10 is in a position rotated 180 ° in the right or left turning direction from the neutral operation position.

  As can be seen from the figure, when the steering wheel 10 is rotated 90 degrees in the right or left turning direction from the neutral operation position, the lower shaft 60 rotates 90 degrees about its own rotation axis. The shaft 88 does not rotate up to 90 ° about its own rotation axis, and the rotation angle of the input side shaft 88 is less than 90 °. When the steering wheel 10 is further rotated and rotated 180 degrees in the right or left turning direction from the neutral operation position, both the lower shaft 60 and the input side shaft 88 rotate 180 degrees. As shown in FIG. 7, the relationship between the rotation angle α of the lower shaft 60 and the rotation angle β of the input side shaft 88 is such that when the steering wheel 10 is rotated less than 180 ° from the neutral operation position, the input side shaft The rotation angle β of 88 is smaller than the rotation angle α of the lower shaft 60. When the steering wheel 10 is rotated 180 ° from the neutral operation position, the rotation angle β of the input side shaft 88 is the same as the rotation angle α of the lower shaft 60. It becomes. That is, when the rotational phase of the lower shaft 60 is a specific rotational phase in which the rotational phase of the lower shaft 60 and the rotational phase of the input side shaft 88 coincide with each other, specifically, the rotational angle α of the lower shaft 60 is 0. When the angle is 180 ° or 180 °, the rotation angles α and β are the same, and the rotation phase difference is zero. On the other hand, while the rotation angle α of the lower shaft 60 changes from 0 ° to 180 °, the rotation phase difference gradually increases, and gradually decreases from a certain rotation angle to zero. The gear ratio (dβ / dα) of the two shafts 60 and 88 in this case, that is, the ratio (dβ / dt) of the rotational speed (dβ / dt) of the input side shaft 88 to the rotational speed (dα / dt) of the lower shaft 60. As shown in FIG. 8, dα) varies according to the rotation angle α of the lower shaft 60.

  As can be seen from the figure, when the rotation angle α of the lower shaft 60 is 0 °, the gear ratio (dβ / dα) is the smallest, and the gear ratio (dβ / dα) increases as the rotation angle α of the lower shaft 60 increases. Becomes bigger. That is, in the steering column 12, when the operation angle of the steering wheel 10 is small, gentle and stable handling is realized, and as the operation angle of the steering wheel 10 increases, handling with good response is realized. It is. In the present system, the operation range of the steering wheel 10 is limited to about 180 ° left and right from the neutral operation position by an operation range limiting mechanism (not shown).

  Incidentally, e shown on the vertical axis of FIG. 8 is the rotation axis of the input side shaft 88 with respect to the offset amount L (FIG. 4) from the rotation axis of the input side shaft 88 at the position where the roller 122 is engaged with the groove 114. And the rotation axis of the lower shaft 60 is a ratio of a deviation amount d (FIG. 4), which affects the operation feeling of the steering wheel 10.

<Control of steering system>
The steering assist control in the ECU 180 is control related to the steering assist device 82 described above, and specifically, is control of the motor 80 included in the steering assist device 82. In this control, first, the steering torque T _S as the steering force applied to the steering wheel 10 based on the relative rotational displacement amount θ between the upper end portion and the lower end portion of the torsion bar 90 detected by the relative displacement amount sensor 108. Is estimated. Next, a target supply current i ^* = K _i · T _A ^* (K _i) that is a target for the motor 80 so as to generate a target assist torque T _A ^* that is an assisting force according to the estimated steering torque T _S. : Gain) is determined. Based on the target supply current i ^* , a target duty ratio is determined, and a command based on the duty ratio is transmitted to the inverter 182. The inverter 182 controls the opening and closing of the switching element included in the inverter 182 under the appropriate duty ratio, and operates the motor 80 so as to generate the target assist torque T _A ^* . Hereinafter, a method for determining the target assist torque T _A ^* will be described in detail.

i) Standard Control The target assist torque T _A ^* is basically the standard assist torque T _B (T _S) defined to increase with the increase of the steering torque T _S as shown by the solid line in FIG. ) To be determined. As can be seen from the figure, the standard assist torque T _B (T _S ) is defined such that its gradient of change gradually increases with an increase in the steering torque T _S , and the driver feels that the steering is heavy. A steering feeling that can not be obtained. The target assist torque T _A ^* is limited to a limit torque T _Alimit or less in consideration of the upper limit value of the output of the motor 80.

ii) Significance of assisting force suppression control As described above, the steering system includes a steering force transmission mechanism having a structure in which the steering gear ratio dβ / dα changes in accordance with the operation angle of the steering wheel 10. Therefore, since the operation range of the steering wheel 10 is set to about 180 ° to the left and right from the neutral operation position, the operation range is small and the steering gear ratio is relatively large compared to a general vehicle, and the configuration is simple. In other words, the turning amount of the turning device with respect to the operation angle of the steering wheel 10 is large. That is, since it is necessary to make a large turn with small steering, this steering system requires a relatively large assist torque. In the steering force transmission mechanism, the steering gear ratio increases as the operating angle increases. In such a case, a larger assist torque is required. In this system, the assist torque is limited to the limit torque T _Alimit. Can be reached relatively easily.

When the target assist torque is limited, the driver's steering feeling changes suddenly. Therefore, in order to prevent a sudden change in the steering feeling, the present steering system is an assist control that suppresses the assist torque instead of the standard control that generates the assist torque according to the standard assist torque T _B (T _S ). The power suppression control is configured to be executable.

In iii) assist force suppressing control the system, if the steering torque T _S has satisfied the start condition in the process of increasing, is switched to the assist force suppressing control from the standard control. The start condition is set using the operation angle δ detected by the operation angle sensor 184 and the steering speed ω of the steering wheel 10 obtained from the detection result of the sensor 184 as parameters. Specifically, the first condition is that the steering speed ω is equal to or higher than the threshold speed. However, as shown in FIG. 10, the threshold speed is set to a smaller value when the steering torque T _S is larger than when the steering torque T _S is small. Incidentally, the threshold speed can be changed according to the target assist torque, its supply current, supply power, etc., instead of the steering torque.

When the steering speed ω is equal to or lower than the threshold speed ω _B (T _S ), it is determined as a second condition whether or not the operation angle δ is equal to or greater than the threshold operation angle. In other words, even if the steering speed ω is equal to or lower than the threshold speed ω _B (T _S ), when the operation angle δ is equal to or higher than the threshold operation angle δ _B (ω), the standard control is switched to the assisting force suppression control. is there. As shown in FIG. 11, the threshold operation angle is set according to the steering speed ω, and is set to a smaller value when the steering speed ω is large than when it is small.

In the assisting force suppression control executed when the above starting condition is satisfied in the process of increasing the steering torque T _S , the target assist torque T _A ^* is the suppression assist torque T _R defined according to the steering torque T _S. It is determined to be (T _S ). The suppression assist torque T _R (T _S ) is, as shown by a one-dot chain line in FIG. 9 (two examples are described), a steering torque T when the condition is satisfied, which is a steering torque when the start condition is satisfied. _The standard assist torque T _B (T _S0 ) corresponding to _S0 is specified to increase as the steering torque increases and to be smaller than the standard assist torque T _B (T _S ) for the same steering torque T _S. . Specifically, the suppression assist torque T _R (T _S ) is defined such that the change gradient thereof is constant (change gradient: k) with respect to the increase in the steering torque T _S. In this system, the change gradient of the suppression assist torque T _R (T _S ) is the same gradient regardless of the condition-fulfilled steering torque T _S0 . That is, in the assisting force suppression control, the target assist torque T _A ^* is determined according to the following equation.
T _A ^* = T _B (T _S0 ) + k · (T _S −T _S0 )

The assisting force suppression control is continuously executed until the end condition is satisfied. Then, the steering torque T _S is, be a time of the steering torque T _S0 following the condition satisfaction is set as the end condition. In other words, in this system, at a process of steering torque T _S is reduced during execution of the assisting force suppression control, the assist torque is changed as going back on line traced at increasing process, the steering torque condition After returning to the full steering torque T _S0 , it changes so as to follow a line segment defined by the standard assist torque T _B (T _S ), that is, it returns to the standard control. Note that also in the assisting force suppression control, the target assist torque T _A ^* is limited to be equal to or less than the limit torque T _Alimit .

<Control program>
The above-described steering assist device 82 is controlled by the ECU 180 repeatedly executing the steering assist control program shown in the flowchart of FIG. 12 at short time intervals while the ignition switch is in the ON state. Done. The control flow will be briefly described below with reference to the flowchart shown in the figure.

In the processing by the steering assist control program, an execution control flag FL indicating which of the standard control and the assist force suppression control is being executed is adopted, and the flag value of the flag FL is determined by the standard control. It is set to 0 when it is being executed, and is set to 1 when the assisting force suppression control is being executed. In the processing according to this program, first, in step 1 (hereinafter abbreviated as “S1”, other steps are the same) and S2, the output side shaft 86 and the input side shaft 88 detected by the relative displacement sensor 108 The steering torque T _S is estimated based on the relative rotational displacement amount θ. Next, in S3, a process for switching the control being executed, that is, a process for determining whether or not the above-described start condition or end condition is satisfied is an execution control switching process subroutine whose flowchart is shown in FIG. This is done by executing.

  In the execution control switching process, first, in S21, the flag value of the execution control flag FL is confirmed. When the flag value of the execution control flag FL is 0, the standard control is being executed at the present time. Therefore, whether or not to switch to the assisting force suppression control is determined in S22 and subsequent steps. On the other hand, when the flag value of the execution control flag FL is 1, since the assisting force suppression control is currently being executed, it is determined in S29 whether or not to switch to the standard control.

When the flag value of the execution control flag FL is 0, first, in S22, it is confirmed whether or not the steering force of the steering wheel 10 is in the process of increasing. A determination is made whether the start condition is satisfied. Specifically, in S23 and 24, the operation angle δ of the steering wheel 10 is acquired by the operation angle sensor 184, and the steering speed ω of the steering wheel 10 is calculated based on the operation angle δ. Next, in S25, it is determined whether or not the steering speed ω is equal to or higher than the threshold speed ω _B (T _S ) shown in FIG. 10, and in S26, the operation angle δ is the threshold operation angle δ _B shown in FIG. It is determined whether or not (ω) or more. If neither condition is satisfied, it is not necessary to suppress the assisting force, so the flag value of the execution control flag FL is not changed and remains 0.

Further, when any of the conditions is satisfied, more specifically, when the steering speed ω is equal to or higher than the threshold speed ω _B (T _S ), or the steering speed ω is equal to or lower than the threshold speed ω _B (T _S ). When the operation angle δ becomes equal to or greater than the threshold operation angle δ _B (ω) with respect to the steering speed ω, the control is switched from the standard control to the assisting force suppression control. Specifically, in S27, the steering torque T _S estimated in S2 of the steering assist control program is recognized as the condition satisfaction steering torque T _S0 , and in S28, the flag value of the execution control flag FL is set to 1. Changed to

On the other hand, when the flag value of the execution control flag FL is 1 in S21, in S29, it is determined whether or not the above-described termination condition is satisfied, specifically, in the steering assist control program. It is determined whether or not the steering torque T _S estimated in S2 is less than or equal to the condition-fulfilled steering torque T _S0 . If the steering torque T _S is greater than the condition satisfaction steering torque T _S0 , the flag value of the execution control flag FL is not changed and remains 1, and if it is equal to or less than the condition satisfaction steering torque T _S0 , in S30, The flag value is changed to 0.

After the execution control switching process is completed, the flag value of the execution control flag FL is confirmed again in S4 of the steering assist control program. When the flag value of the execution control flag FL is 0, standard control after S5 is executed, and when the flag value is 1, assisting force suppression control after S6 is executed. More specifically, when the standard control is executed, the target assist torque T _A ^* is determined based on the map data of the standard assist torque T _B (T _S ) shown by the solid line in FIG. When assisting force suppression control is executed, the target assist torque T _A ^* is determined according to the formula T _A ^* = T _B (T _S0 ) + k · (T _S −T _S0 ).

As described above, after ^{the *} target assist torque T _A is determined, in S7, ^* the target assist torque T _A is, it is determined whether the limit torque T _Alimit greater than is greater than the limit torque T _Alimit In this case, the target assist torque T _A ^* is set as the limit torque T _Alimit . Then, in S9, based on the determined target assist torque T _A ^*, supply current i ^* is determined as a target. In S10, a duty ratio for controlling the motor 80 is determined based on the determined target supply current i ^* , and a command based on the duty ratio is transmitted to the inverter 182. By controlling the operation of the motor 80 of the steering assist device 82 by such processing, the steering assist device 30 generates the required assisting force.

<Functional configuration of control device>
The ECU 180, which is the control device of the steering system, executes various processes as described above by executing the steering assist control program described above. By executing these various processes, the ECU 180 can be considered to have a functional unit as shown in FIG. The ECU 180 includes a standard control unit 200 that executes standard control for causing the steering assist device 82 to generate the assisting force that becomes the standard assist torque T _B (T _S ) and the assist that becomes the suppression assist torque T _R (T _S ). And an assisting force suppression control unit 202 that executes assisting force suppression control for generating a force. The standard control unit 200 corresponds to a part that executes the processes of S5, S9, and S10 of the steering assist control program, and the assisting force suppression control part 202 includes a part that executes the processes of S6, S9, and S10 of the program. Equivalent to. Further, the ECU 180 executes the execution control switching process subroutine to switch from the standard control to the assisting force suppression control when the above-described start condition is satisfied, and from the assisting force suppression control to the standard control when the end condition is satisfied. An execution control switching unit 204 is provided as a switching function unit. Further, the ECU 180 executes the processing of S7 and 8 of the steering assist control program in both the standard control and the assisting force suppression control, and the assisting force to be generated by the steering assisting device 82 is the setting force. When the torque exceeds the limit torque T _Alimit , the assisting force limiting unit 206 limits the assisting force generated by the steering assisting device 82 to the set force.

<Effect of this steering system>
As described above, in this system, the assist torque is controlled both when switching from the standard control to the assist force suppression control and when switching from the assist force suppression control to the standard control. There is no sudden change and the change in the steering feeling of the driver is made relatively small, so that it is possible to suppress the uncomfortable feeling experienced by the driver due to the switching of control. Further, the assisting force suppression control makes it difficult for the target assist torque to easily reach the limit torque, and the steering feeling suddenly changes due to reaching the limit torque as much as possible.

  Furthermore, when the start condition of the assisting force suppression control is set based on the steering speed, and the burden on the motor 80 is predicted to increase, the assisting force is effectively suppressed, The burden on the motor 80 can be reduced. Incidentally, the standard assist torque in the standard control is set relatively high in consideration of the case where there are many occupants of the vehicle. Therefore, when the number of occupants is small, the steering speed is increased even if the steering torque is small. When the motor 80 cannot follow the steering speed, the driver's steering feeling changes suddenly, but the starting condition of the assisting force suppression control is set based on the steering speed. Thus, the situation where the steering feeling suddenly changes due to steering when the number of passengers is small is avoided as much as possible.

  Furthermore, when the start condition is set based on the steering amount, and it is predicted that the steering wheel 10 is limited by the operation range limiting mechanism, the assisting force is suppressed, so that the steering wheel 10 It is possible to effectively mitigate the impact when the operating range is limited by the operating range limiting mechanism.

  Since the steering system includes the steering force transmission mechanism having a structure in which the steering gear ratio changes according to the operation angle of the steering wheel 10 as described above, the lock-to-lock of the steering wheel 10 is It is 360 °. As a result, compared to a general vehicle, the steering amount is large even with the same steering amount, and thus a large assisting force is often required. The assisting force suppression control described above is particularly effective in the present steering system that is likely to be in a situation where a large assisting force is generated.

<Modification>
In the above-described embodiment, the suppression assist torque T _R (T _S ), which is the assist force that should be generated in the steering assist device 82 in the assist force suppression control, depends on the condition-fulfilled steering torque T _S0 . Although the slopes are always the same, it is possible to change the slope in accordance with the steering torque T _S0 when the condition is satisfied. For example, in the steering system of the first modified example, as shown in FIG. 15A, the suppression assist torque T _R (T _S ) has a standard assist torque corresponding to the condition satisfaction steering torque T _S0 , the origin O, Is defined by a straight line passing through. That is, the in the system of the first modification, the greater condition satisfaction when the steering torque T _S0 is, since the slope becomes larger, the greater condition satisfaction when the steering torque T _S0 is, so that the emphasis on steering wheel. Further, for example, in the steering system of the second modified example, as shown in FIG. 15B, the suppression assist torque T _R (T _S ) has a standard assist torque corresponding to the condition satisfying steering torque T _S0 , and The standard assist torque T _B (T _S ) is defined by a straight line passing through a fixed point A set at a steering force larger than the defined steering force. That is, the in the second modification systems, larger condition satisfaction when the steering torque T _S0 is, since the slope becomes smaller, the greater condition satisfaction when the steering torque T _S0 is, so that the focus on the suppression of assist force.

1 is a schematic diagram showing a vehicle steering system that is an embodiment of the claimable invention. FIG. It is sectional drawing which shows the steering column with which the vehicle steering system of FIG. 1 is provided. It is sectional drawing which shows the EPS section with which a steering column is provided. FIG. 4 is a cross-sectional view taken along line AA ′ shown in FIG. 3. It is a perspective view which shows the breakaway bracket holding the column section with which a steering column is provided. FIG. 4 is a cross-sectional view taken along line AA ′ shown in FIG. 3 when the steering wheel is rotated. It is a graph which shows the relationship between the rotation angle of an operation member side shaft, and the rotation angle of a steering apparatus side shaft. It is a graph which shows the gear ratio of the operating member side shaft and the steering apparatus side shaft which change according to the rotation angle of the operating member side shaft. It is a figure which shows the relationship between steering torque and the assist torque which should be generated in the steering assistance apparatus shown in FIG. It is a figure which shows the magnitude | size with respect to the steering torque of the steering speed which is a parameter of the conditions for starting assisting force suppression control. It is a figure which shows the magnitude | size with respect to the steering speed of the steering amount which is a parameter of the conditions for starting assisting force suppression control. It is a flowchart showing the steering assistance control program performed by the steering electronic control unit shown in FIG. It is a flowchart which shows the execution control switching process subroutine which is a part of steering assistance control program of FIG. It is a block diagram regarding the function of the steering electronic control unit shown in FIG. It is a figure which shows the relationship between the steering torque in the steering system of a modification, and the assist torque which should be generated in a steering assistance apparatus.

Explanation of symbols

10: Steering wheel (steering operation member) 12: Steering column (steering force transmission mechanism) 14: Steering device 16: Intermediate shaft (steering force transmission mechanism) 18: Output shaft (first shaft) 50: Column section 52 : EPS section 54: Main shaft (second shaft) 80: Electromagnetic motor (drive source) 82: Steering assist device 86: Output side shaft 88: Input side shaft 90: Torsion bar 108: Relative displacement sensor [θ] 114 : Groove (guide passage)
116: annular plate 118: pin 120: needle bearing 122: roller 126: pair of side wall surfaces 180: steering electronic control unit (ECU) 182: inverter 184: operation angle sensor [δ] 200: standard control unit 202: assistant Force suppression control unit 204: Execution control switching unit 206: Supporting force limiting unit

α: rotation angle of the lower shaft β: rotation angle of the input shaft dβ / dα: gear ratio L: offset amount of the engagement position d: displacement amount of the two shafts e: ratio δ: operation angle (steering amount) θ : Relative rotational displacement T _S : Steering torque (steering force) T _A ^* : Target assist torque i ^* : Target supply current T _B (T _S ): Standard assist torque T _Alimit : Limit torque ω: Steering speed ω _B (T _S ): Threshold speed δ _B (ω): Threshold operating angle T _R (T _S ): Suppression assist torque

Claims (6)

A steering operation member operated by the driver;
A steering device for turning the wheels so that the steering amount is in accordance with the steering amount of the steering operation member;
A steering force transmission mechanism that transmits a steering force applied to the steering operation member to the steering device;
A steering assist device that has a drive source and generates an assist force for assisting the steering of the wheel based on the force generated by the drive source;
And a control device that controls the drive source of the steering assist device and controls the assist force generated by the steering assist device based on the steering force of the steering operation member. And
The control device is
A standard control unit that executes standard control for controlling the drive source so that the assisting force generated by the steering assisting device is a standard assisting force that is defined to increase with an increase in steering force;
When the first setting condition is satisfied in the process of increasing the steering force, instead of the standard control, the steering force generated by the steering assist device at the time when the first setting condition is satisfied The drive source is adjusted so that the standard assisting force corresponding to the steering force when the condition is satisfied increases as the steering force increases and becomes a restraining assisting force defined to be smaller than the standard assisting force. possess the assist force suppressing control unit for executing the assist force suppressing control for controlling,
When the steering speed of the steering operation member is equal to or higher than a threshold speed, the assisting force suppression control unit is configured to execute the assisting force suppression control by assuming that the first setting condition is satisfied . Steering system. When the steering amount of the steering operation member is greater than or equal to a threshold steering amount, the assisting force suppression control is executed by the assisting force suppression control unit, assuming that the first setting condition is satisfied. vehicle steering system according to claim 1 configured to. A steering operation member operated by the driver;
A steering device for turning the wheels so that the steering amount is in accordance with the steering amount of the steering operation member;
A steering force transmission mechanism that transmits a steering force applied to the steering operation member to the steering device;
A steering assist device that has a drive source and generates an assist force for assisting the steering of the wheel based on the force generated by the drive source;
A control device that controls the drive source of the steering assist device and controls the assisting force generated by the steering assist device based on the steering force of the steering operation member;
A vehicle steering system comprising:
The control device is
A standard control unit that executes standard control for controlling the drive source so that the assisting force generated by the steering assisting device is a standard assisting force that is defined to increase with an increase in steering force;
When the first setting condition is satisfied in the process of increasing the steering force, instead of the standard control, the steering force generated by the steering assist device at the time when the first setting condition is satisfied The drive source is adjusted so that the standard assisting force corresponding to the steering force when the condition is satisfied increases as the steering force increases and becomes a restraining assisting force defined to be smaller than the standard assisting force. An assisting force suppression control unit for executing the assisting force suppression control to be controlled;
Have
A vehicle configured to execute the assisting force suppression control by the assisting force suppression control unit assuming that the first setting condition is satisfied when the steering amount of the steering operation member is equal to or greater than a threshold steering amount. Steering system. The control device is
Even if the first setting condition is no longer satisfied during the execution of the assisting force suppression control, the assisting force suppression control unit performs the assisting force suppression control until the second setting condition is satisfied. The vehicle steering system according to any one of claims 1 to 3, wherein the vehicle steering system is configured to be continuously executed. The control device is
When the steering force decreases below the steering force when the condition is satisfied in the process of decreasing the steering force, the assisting force suppression control is switched to the standard control assuming that the second setting condition is satisfied. The vehicle steering system according to claim 4 . The standard assisting force is defined such that the gradient of change with respect to an increase in its steering force is gradually increased;
The vehicle steering system according to any one of claims 1 to 5, wherein the suppression assisting force is defined such that a gradient of change with respect to an increase in the steering force is constant.

Images