JP2012166592A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device suppressing yaw responsibility to disturbance from a road surface near a neutral position of a steering wheel making the yaw responsibility during steering operation of a driver good.SOLUTION: In the electric power steering device in which a magnetostrictive torque sensor is arranged in an steering force transmission passage extending the steering wheel to a steered wheels and which drives a steering actuator according to the steering torque detected by the magnetostrictive torque sensor and thereby assists the steering operation of the driver by driving a steering actuator, the steering gear box arranged between the steering wheel and the steered wheels is supported on the vehicle body via a rubber bush 42 with a lesser spring constant than that of the magnetostrictive torque sensor. The rubber bush 42 has a pair of hollow parts 42a, 42a in the peripheral directional area in a rack shaft direction of the outer peripheral part of the same.

Description

  In the present invention, a magnetostrictive torque sensor is disposed in a steering force transmission path from a steering wheel to a steered wheel, and a steering actuator is driven according to the steering torque detected by the magnetostrictive torque sensor to assist a driver in steering operation. The present invention relates to an electric power steering apparatus.

  Patent Document 1 discloses a technique for detecting a steering force input to a steering wheel using a magnetostrictive torque sensor and calculating a target torque to be generated by a motor of an electric power steering device based on the detected steering torque. . The magnetostrictive torque sensor includes a magnetostrictive film formed so as to have magnetic anisotropy on the outer periphery of the pinion shaft, and a detection coil surrounding the outer periphery of the magnetostrictive film, and changes according to the torsional strain of the pinion shaft. The steering torque of the pinion shaft is detected by detecting the change in the magnetic permeability as the change in the inductance of the detection coil.

  Also, in Patent Document 2, the input shaft and the output shaft are connected by a torsion bar, and the relative rotation of the input shaft and the output shaft that occurs when the torsion bar is twisted by a steering force, the movable member is displaced in the axial direction. A technique of a torsion bar type steering torque sensor that detects a steering torque by converting and detecting a position of a core provided on a movable member with a detection coil is described.

  By the way, if the torsional rigidity of the steering force transmission path connecting the steering wheel and the steered wheels is high, the steering force input from the driver or the steering actuator is directly transmitted to the wheels that are the steered wheels. There is a tendency for responsiveness to increase. Conversely, if the torsional rigidity of the steering force transmission path is low, the yaw response tends to be low. However, when a torsion bar type steering torque sensor is adopted, the torsion bar torsional rigidity is the lowest in the steering force transmission path, and therefore the upper limit value of the yaw response of the vehicle is limited by the torsion bar torsion, There is a problem that the yaw responsiveness cannot be set high, and the driver does not give a driving feeling of good vehicle motion.

On the other hand, when a magnetostrictive torque sensor such as a torsion bar having no small spring constant is employed, the torsional rigidity of the steering force transmission path is increased, and the vehicle yaw response is fixed to a high value. There is a problem that the driver is not given a driving feeling of good vehicle motion.
Therefore, as an improved technique, Patent Document 3 discloses that a magnetostrictive torque sensor is arranged in a steering force transmission path from the steering wheel to the steered wheel, and the steering actuator is driven according to the steering torque detected by the magnetostrictive torque sensor. In an electric power steering apparatus that assists a driver's steering operation, a technique for supporting a steering gear box disposed between a steering wheel and a steered wheel on a vehicle body via an elastic body is disclosed.

JP 2006-7931 A JP 2006-232214 A JP 2008-168798 A

  However, in the technique described in Patent Document 3, in the structure in which the steering gear box is supported on the vehicle body via the elastic body, the relative movement amount is smaller than the relative movement amount of the elastic body with respect to the vehicle body in the rack axis direction. When increased, the repulsive force of the elastic body also corresponds to the deflection amount-load characteristic curve of the elastic body accordingly. As a result, for example, even when the steering wheel is in the neutral position, when the steered wheels are subjected to a disturbance such as a kickback from the road surface and receive an impact in the rack axis direction, the elastic body is sufficient in the rack axis direction. There is a possibility that the shock cannot be absorbed, and a signal indicating the fluctuation of the steering torque is generated from the magnetostrictive torque sensor, and the steering actuator is driven in response to the yaw motion of the vehicle.

  The present invention solves the above-described conventional problems, and suppresses the yaw response to a disturbance from the road surface near the neutral position of the steering wheel, and the yaw response during the steering operation of the driver is It is an object of the present invention to provide an electric power steering device that is satisfactory.

  In order to solve the above-mentioned problem, a first aspect of the invention relates to a steering actuator in which a magnetostrictive torque sensor is disposed in a steering force transmission path from a steering wheel to a steered wheel, and the steering actuator is detected according to the steering torque detected by the magnetostrictive torque sensor. In the electric power steering device that assists the steering operation of the driver by driving the steering wheel, the steering gear box disposed between the steering wheel and the steered wheels is attached to the vehicle body via an elastic body having a smaller spring constant than the magnetostrictive torque sensor. The elastic body is provided with a body support portion for supporting, and the elastic body generates a load in a direction opposite to the direction of the relative movement according to the relative movement amount of the steering gear box relative to the vehicle body. The slope of the increase amount is more relative to the relative movement amount than when the relative movement amount is less than or equal to a predetermined value. Characterized in that the larger time than a predetermined value.

According to the first aspect of the present invention, when the relative movement amount of the steering gear box with respect to the vehicle body is equal to or smaller than a predetermined value by the steering operation of the driver, the gradient of the increase amount of the load with respect to the relative movement amount is inclined. small. That is, when the steering wheel is moved from the neutral position to the left or right by a predetermined angle or less, the relative movement amount increases greatly with respect to the external force, and the steering torque detected by the magnetostrictive torque sensor is suppressed to be small, so that the steering assist force is hardly generated. In other words, in the vicinity of the neutral position of the steering wheel, the yaw responsiveness of the electric power steering device is suppressed, and the electric power steering device is suppressed from responding excessively to disturbances such as kickback from the road surface. To improve the ride comfort.
On the other hand, when the relative movement amount of the steering gear box with respect to the vehicle body is equal to or larger than a predetermined value set in advance, the gradient of the increase in load with respect to the relative movement amount is large. That is, when the steering operation amount is equal to or greater than the predetermined angle, the further increase in the relative movement amount is small and the steering torque detected by the magnetostrictive torque sensor is large, so that a steering assist force is likely to be generated. That is, the yaw response of the electric power steering device is increased, and the intended turning motion of the vehicle can be quickly performed.

  According to a second aspect of the invention, in addition to the configuration of the first aspect of the invention, the vehicle body support portion further includes an outer cylinder, an inner cylinder disposed on the radially inner side of the outer cylinder, and an outer cylinder. It has a rubber bush joint including an elastic body between the inner cylinder, the outer cylinder is fitted into a hole provided in the steering gear box, and the inner cylinder is supported by the vehicle body with bolts. The elastic body is characterized by having a predetermined gap between the outer cylinder and at least a part of the outer peripheral portion thereof.

  According to the invention of claim 2, the outer cylinder of the rubber bush joint is fitted into a hole provided in the steering gear box, and the inner cylinder is supported by the vehicle body with the bolt, and the elastic body is Since at least a part of the outer peripheral portion has a predetermined gap between the outer cylinder and the outer cylinder, the elastic body is elastic against bending of the gap in the predetermined gap direction with the outer cylinder. The spring constant generated in the body can be set to a relatively small value, and the gap can be eliminated and the outer cylinder and the outer peripheral portion of the elastic body can be set to a relatively large spring constant after contact.

  Therefore, the predetermined gap is preferably provided in a circumferential region in the direction in which the steering gear box moves relative to the vehicle body. Specifically, the predetermined gap is provided on both the left and right sides in the rack axis direction. It is preferable to provide it.

  The invention according to claim 4 is a rubber bush joint in which the vehicle body support portion includes an outer cylinder, an inner cylinder disposed on the radially inner side of the outer cylinder, and an elastic body between the outer cylinder and the inner cylinder. The outer cylinder is fitted into a hole provided in the steering gear box, the inner cylinder is supported by the vehicle body with bolts, and the elastic body has a substantially annular shape, A space portion having a predetermined gap is provided in a direction region in which the steering gear box in the circumferential portion moves relative to the vehicle body.

According to the invention of claim 4, the outer cylinder of the rubber bush joint is fitted into a hole provided in the steering gear box, the inner cylinder is supported by the vehicle body with the bolt, and the elastic body is , Having a substantially annular shape and having a predetermined space between the outer cylinder and a space portion having a predetermined gap in a direction region in which the steering gear box of the circumferential direction portion moves relative to the vehicle body. For the deflection of the elastic body corresponding to the gap in the gap direction, the spring constant generated in the elastic body can be set to be relatively small, and the elastic body can be set to a relatively large spring constant after the bending gap is eliminated.
Therefore, the predetermined gap is preferably provided in a direction in which the steering gear box moves relative to the vehicle body, and specifically, the predetermined gap is preferably provided on both the left and right sides in the rack axis direction. .

  According to the present invention, there is provided an electric power steering apparatus that suppresses yaw response to a disturbance from a road surface in the vicinity of a neutral position of a steering wheel and that provides good yaw response during a steering operation by a driver. Can be provided.

1 is an overall structural diagram of an electric power steering apparatus according to an embodiment. It is an AA arrow expanded sectional view in FIG. It is a BB arrow sectional view of a rubber bush in Drawing 1, (a) is the 1st example of BB arrow sectional shape of a rubber bush, (b) is a BB arrow view of a rubber bush. It is 2nd Example of cross-sectional shape. It is explanatory drawing of the spring characteristic with respect to the bending (or relative displacement of a steering gear box and a vehicle body) of the rack axis direction of a rubber bush. It is the C section enlarged view of the magnetostrictive torque sensor part in FIG. It is explanatory drawing which shows the change characteristic of the torque detection signal with respect to steering torque. It is 3rd Example of the BB arrow cross-sectional shape of the rubber bush in FIG.

  Hereinafter, an electric power steering apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings.

  The electric power steering apparatus according to this embodiment will be described with reference to FIGS. FIG. 1 is an overall structural diagram of an electric power steering apparatus according to an embodiment.

<< Overall structure of electric power steering system >>
As shown in FIG. 1, the electric power steering apparatus includes an upper steering shaft 12 that rotates integrally with a steering wheel 11, a lower steering shaft 14 that is connected to the upper steering shaft 12 via an upper universal joint 13, and a lower steering. A rack and pinion type steering gear box 16 connected to the shaft 14 via a lower universal joint 15 and a steering actuator 17 provided on the upper steering shaft 12 are provided.

The steering gear box 16 includes a rack shaft 19 on which rack teeth 18 are formed, a pinion gear 20 having a pinion gear 20 that meshes with the rack teeth 18, and a pinion shaft 21 connected to the lower universal joint 15. And a housing 24 that supports the pinion shaft 21 via a pair of bearings 22 and 23 at a position sandwiching the pinion gear 20 in the vertical direction.
The left and right ends of the rack shaft 19 are connected to the steered wheels W and W, which are left and right front wheels, via left and right ball joints 25 and 25 and left and right tie rods 26 and 26, respectively.
Incidentally, the steered wheel W on the left side in FIG. 1 represents the right front wheel in FIG. 1, and the steered wheel W on the right side in FIG. 1 represents the left front wheel.
The steering wheel 11, the upper steering shaft 12, the upper universal joint 13, the lower steering shaft 14, the lower universal joint 15, the pinion shaft 21, the pinion gear 20, the rack teeth 18, the rack shaft 19, the left and right ball joints 25, 25, the left and right The tie rods 26 and 26 and the steered wheels W and W correspond to the “steering force transmission path from the steering wheel to the steered wheels” recited in the claims, and are also referred to as “steering system” below.

《Support structure for steering gear box》
Next, a support structure for the steering gear box 16 will be described with reference to FIGS. 1, 2, and 3.
FIG. 2 is an enlarged cross-sectional view taken along line AA in FIG. FIG. 3 is a cross-sectional view of the rubber bush in FIG. 1 taken along the line B-B. FIG. 3A is a first example of the cross-sectional shape of the rubber bush taken along the line B-B, and FIG. It is 2nd Example of -B arrow cross-sectional shape.
As shown in FIG. 1, the steering gear box 16 has at least two rubber bush joint arms 71 extending outward from the housing 24 at a predetermined distance in the rack axis direction. And it is supported (refer FIG. 2) by the attachment member 39a of the vehicle body 39 (refer FIG. 2) via the rubber bush 42 which is an elastic body fixed to the rubber bush joint arm 71. As shown in FIG. That is, as shown in FIG. 1, the housing 24 of the steering gear box 16 is elastically supported by the vehicle body 39 via the two rubber bush joints 38.

As shown in FIG. 2, each rubber bush joint 38 includes an outer cylinder 40, an inner cylinder 41, and a rubber bush 42. The outer cylinder 40 is press-fitted into an attachment hole (a hole provided in the steering gear box) 71a provided in the rubber bush joint arm 71 of the housing 24, and the outer cylinder 40 and the attachment hole 71a are relatively circumferential. It is fitted so that it cannot rotate. The inner cylinder 41 is fixed with bolts 43 to, for example, two upper and lower attachment members 39 a of the vehicle body 39. The spring constants of the rubber bush joints 38 are set to be smaller than the spring constant of the magnetostrictive torque sensor 34 (see FIG. 1).
By the way, discrete irregularities are provided in the circumferential direction on the inner circumferential surface of the mounting hole 71a, and when the outer cylinder 40 is press-fitted, the outer circumferential surface of the outer cylinder 40 is distorted by the irregularities, and the rubber bush joint 38 is attached to the mounting hole. After attaching to 71a, the fixing property may be improved so that the attachment hole 71a and the outer cylinder 40 do not rotate relatively in the circumferential direction.

FIG. 4 is an explanatory diagram of spring characteristics with respect to the bending of the rubber bush in the rack axis direction (or relative movement amount between the steering gear box and the vehicle body). The horizontal axis indicates the amount of deflection δ of the rubber bush 42 in the rack axis direction, and the vertical axis indicates the load F in the rack axis direction required to generate the amount of deflection δ. The spring characteristic curve X for the deflection in the rack axis direction is XA when the deflection amount δ is 0 to E1, and is XB when the deflection amount δ is E1 or more, as shown in FIG. The slope is XA <XB. The load in the rack axis direction at which the deflection amount δ is E1 is F1.
For the sake of convenience, the amount of deflection δ from 0 to E1 is referred to as “shear region R1”, and the amount of deflection δ of E1 or more is referred to as “compression region R2”.

The rubber bushing 42 has a substantially annular shape as shown in the first and second embodiments of the rubber bushing 42 shown in FIGS. 3A and 3B. A pair of straight portions (gap and space) 42a and 42a are provided in a circumferential region portion facing each other. The straight portion 42a has a gap of a predetermined width E1, and the thickness of the portion to the outer peripheral surface of the inner cylinder 41 of the rubber bush 42 in the rack axis direction is E2.
Incidentally, the rubber bush 42 is vulcanized and bonded to the inner peripheral surface of the outer cylinder 40, and is also vulcanized and bonded to the outer peripheral surface of the inner cylinder 41, so It does not rotate in the circumferential direction.

In particular, in the second embodiment of the rubber bush 42 shown in FIG. 3B, recesses 42a ₁ and 42a ₁ on the circumferential surface are provided on both sides in the circumferential direction of the straight portion 42a, and the rubber bush 42 is pushed in the rack axis direction. A shape in which concentrated stress is not applied to the bonded end portions 42a ₂ and 42a ₂ of the outer cylinder 40 and the rubber bushing 42 when bent in the rack axial direction under pressure or tensile force. By providing such depressions 42a ₁ and 42a ₁ , durability of the rubber bushing 42 for fixing to the outer cylinder 40 is improved.

  Thus, by providing the straight portions 42a and 42a at two locations in the outer peripheral area of the rubber bush 42 in the rack axial direction, the steering wheel 11 (see FIG. For example, when the right steered wheel W (the left steered wheel on the plane of FIG. 1) is pushed leftward from the road surface when the vehicle is in a substantially neutral steering position. It is assumed that (rightward force on the paper surface of FIG. 1) is received. Then, the rack shaft 19 is pushed to the right on the paper surface of FIG. 1 via the tie rod 26 and the ball joint 25 on the right front wheel side. At this time, the pinion gear 20 is fixed to a substantially straight steering state by the driver. 1 is converted into a rotational force of the pinion gear 20, and the left side of the housing 24 of the steering gear box 16 via the bearings 22 and 23 (the page of FIG. 1). Pressing in the upper right direction) also occurs.

  The pressing of the housing 24 in the left direction (the right direction in the drawing in FIG. 1) is transmitted to the rubber bush joint arm 71, and the outer cylinder 40 is in the rack axial direction indicated by the arrow (see FIG. 3) with respect to the inner cylinder 41. Cause a relative movement in the right direction of. Until the outer peripheral surface facing the left side straight portion 42a of the left region 42c (see FIG. 3) of the rubber bush 42 abuts on the left inner peripheral surface of the outer cylinder 40 on the paper surface of FIG. The rubber bush 42 bends with the characteristic determined by the spring constant with respect to the shear stress of the regions 42b and 42b of the rubber bush 42 until it is bent by the gap of the width E1, as shown in the shear region R1 of the deflection amount δ shown in FIG. In addition, the gradient XA of the load F with respect to the deflection amount δ is relatively small. That is, since the housing 24 is easy to move rightward on the paper surface of FIG. 1, the amount and force by which the rack teeth 18 rotate the pinion shaft 21 are reduced, and the steering torque detected by the magnetostrictive torque sensor 34 is suppressed. The

As a result, in the electric power steering apparatus using the magnetostrictive torque sensor 34, an excessive response of yaw response that is uncomfortable for the passenger due to the generation of steering torque due to kickback from the road surface of the steered wheels W when the vehicle is traveling straight ahead. Can be suppressed.
Further, as shown in FIG. 4, in the vicinity of the neutrality of the steering wheel 11, the characteristics of the amount of deflection δ and the load F in the rack axial direction of the rubber bush 42 are in the shear region R1. Accordingly, the amount of deflection δ with respect to the change in the load F applied to the rubber bush 42 is increased. Since the load generated in the direction is absorbed by the rubber bush 42, the steered wheels W and W are not steered. That is, it is possible to ensure stability when going straight ahead.

  As described above, the disturbance to the rack shaft 19 in the left direction (right direction on the paper in FIG. 1) has been described as an example, but the same applies to the disturbance to the rack shaft 19 in the right direction (left direction on the paper in FIG. 1). There is an effect.

  Next, a state in which the driver steers the steering wheel 11 to the right, for example, and a steering force in the left direction (the right direction on the paper in FIG. 1) is applied to the rack shaft 19 will be described. In such a case, the steering force in the right direction on the paper surface of FIG. 1 to the rack shaft 19 is directed to the right direction of the housing 24 of the steering gear box 16 via the bearings 22 and 23 (left direction on the paper surface of FIG. 1). The reaction force of also occurs. However, more than that, as the vehicle turns in the right direction, a large force is applied to the load on the front of the vehicle in the left direction of the vehicle (the right direction on the plane of FIG. 1), which exceeds the reaction force described above. Accordingly, the relative movement of the housing 24 in the left-right direction of the rack shaft (rightward on the paper surface of FIG. 1) increases, and the left side of the region 42c on the left side of the rubber bush 42 (right side of the paper surface of FIG. 3). After the outer peripheral surface facing 42a comes into contact with the inner peripheral surface of the outer cylinder 40, the contribution of the spring constant to the shear stress in the regions 42b and 42b of the rubber bush 42 becomes small, and the right rubber on the paper surface of FIG. The spring constant with respect to the compressive stress in the region 42c of the bush 42 becomes dominant, and the gradient XB of the load F with respect to the deflection amount δ becomes relatively large as shown in the compression region R2 of the deflection amount δ shown in FIG.

That is, the housing 24 is less likely to move rightward on the paper surface of FIG. 1, and the rack teeth 18 are almost the rotational force transmitted to the pinion shaft 21, and the steering torque detected by the magnetostrictive torque sensor 34 responds to the road surface reaction force. It will be good.
As a result, in the turning state of the vehicle in the electric power steering apparatus using the magnetostrictive torque sensor 34, the magnetostrictive torque sensor 34 of the upper steering shaft 12 due to the operation of the steering wheel 11 and the reaction force from the road surface of the steered wheels W Steering torque with good responsiveness is generated and can be detected by the magnetostrictive torque sensor 34.

  The state in which the driver steers leftward and a steering force in the right direction (leftward in the drawing of FIG. 1) is applied to the rack shaft 19 will be described in the case of the steering operation in the right direction and the rubber bush 42. The only difference is the direction of the applied force, and it works in the same way.

  Here, the process until the rubber bush 42 is bent in the rack axis direction by the gap of the predetermined width E1 corresponds to “the relative movement amount is equal to or less than a predetermined value” set in the claims, and the rubber bush 42 After the outer peripheral surface facing the straight portion 42a of the region 42c on one of the left and right sides of 42 is in contact with the inner peripheral surface of the outer cylinder 40, the "predetermined relative movement amount is set in advance" Corresponds to when the value is greater than or equal to.

《Steering actuator》
Returning to FIG. 1 again, the configuration of the steering actuator 17 will be described. As shown in FIG. 1, the upper steering shaft 12 is rotatably supported inside a housing 27 via three ball bearings 28, 29, and 30. The steering actuator 17 includes a worm wheel 31 fixed to the upper steering shaft 12, a worm 32 that meshes with the worm wheel 31, and a motor 33 that rotationally drives the worm 32.

《Magnetostrictive torque sensor》
Next, the configuration of the magnetostrictive torque sensor 34 will be described with reference to FIGS. 1, 5, and 6. FIG. 5 is an enlarged view of a portion C of the magnetostrictive torque sensor portion in FIG. 1, and FIG. 6 is an explanatory diagram showing a change characteristic of a torque detection signal with respect to steering torque.
The upper steering shaft 12 above the steering actuator 17 is provided with a magnetostrictive torque sensor 34 that detects a steering torque generated in the upper steering shaft 12 in accordance with the steering force input to the steering wheel 11.

  As shown in FIG. 5, the magnetostrictive torque sensor 34 is made of, for example, Ni—Fe plating formed so as to cover the outer peripheral surface of the upper steering shaft 12 with a predetermined width in the axial direction and over the entire circumference in the circumferential direction. First and second magnetostrictive films 51A and 51B, a first detection coil 52A that faces the first magnetostrictive film 51A and surrounds the upper steering shaft 12 with a predetermined gap radially outward, and a second magnetostrictive film A second detection coil 52B that surrounds the first steering coil 52A, a second detection coil 52B that surrounds the first detection coil 52A, and a second detection coil 52B that surrounds the first steering coil 52A by facing a predetermined gap on the radially outer side of the upper steering shaft 12 A second yoke 53B. First and second output circuits 54A and 54B (see FIG. 1) and a differential amplifier circuit 55 (see FIG. 1) are connected to the first detection coil 52A and the second detection coil 52B.

  Next, the operation of this embodiment will be described. When the driver operates the steering wheel 11, the rotation of the steering wheel 11 causes the upper steering shaft 12, the upper universal joint 13, the lower steering shaft 14, the lower universal joint 15, the pinion shaft 21, the pinion gear 20, the rack teeth 18, and the rack shaft 19. And the left and right steered wheels W, W are steered by being transmitted to the tie rods 26, 26 via the ball joints 25, 25.

  At this time, when the steering torque input to the steering wheel 11 by the driver is detected by the magnetostrictive torque sensor 34 provided around the upper steering shaft 12, an electronic control unit (not shown) is detected by the magnetostrictive torque sensor 34. The motor 33 of the steering actuator 17 is driven according to the steering torque. Torque generated by the motor 33 is transmitted to the upper steering shaft 12 and also to the pinion shaft 21 via the worm 32 and the worm wheel 31, and the steering operation of the driver is assisted by the steering actuator 17.

  The steering torque is detected by the magnetostrictive torque sensor 34 as follows. When an alternating current is supplied to the first and second detection coils 52A and 52B, the first magnetostrictive film 51A corresponds to the steering torque generated in the upper steering shaft 12 when the driver's steering force is input to the upper steering shaft 12. Change from L to L + ΔL, the inductance of the second magnetostrictive film 51B changes from L to L−ΔL, and the change amount ΔL is proportional to the steering torque generated in the upper steering shaft 12. ΔL is detected by the first and second detection coils 52A and 52B.

That is, in FIG. 6, the first voltage signal VT1 output from the first detection coil 52A (see FIG. 5) and the second voltage signal VT2 output from the second detection coil 52B (see FIG. 5) serve as a rectifier circuit. To the first and second output circuits 54A and 54B (see FIG. 1). The first and second output circuits 54A and 54B output first and second voltage signals VT1 ^* and VT2 ^* corresponding to the first and second voltage signals VT1 and VT2, respectively. The first and second voltage signals VT1 ^* and VT2 ^* are input to the differential amplifier circuit 55, where a third voltage signal (torque detection signal) VT3 corresponding to the magnitude of the steering torque is calculated and output. .

Specifically, the differential amplifier circuit 55 third voltage signal by multiplying the gain k to VT1 ^* -VT2 ^* obtained by subtracting from the ^* first voltage signal VT1 second voltage signal VT2 ^* (torque detection signal) VT3 calculate. Since the first voltage signal VT1 ^* increases as the steering torque increases and the second voltage signal VT2 ^* decreases as the steering torque increases, the third voltage signal VT3 increases as the steering torque increases. . When the steering torque is 0, the third voltage signal VT3 is biased so as to become a predetermined bias voltage Vb (for example, 2.5 V).

That is, the third voltage signal VT3 is calculated as in the following equation (1).
VT3 = k (VT1 ^* -VT2 ^* ) + Vb (1)
Thus, when the upper steering shaft 12 is torsionally deformed together with the first and second magnetostrictive films 51A and 51B by the steering force input to the steering wheel 11, the first and second magnetostrictive films 51A and 51B and the first and second magnetostrictive films 51A and 51B. By changing the magnetic flux density along two magnetic paths formed by the two yokes 53A and 53B, the steering torque can be detected based on the change in the magnetic flux density.

  By the way, if the torsional rigidity of the steering force transmission path from the steering wheel 11 to the left and right steered wheels W, W is high, the steering force input by the driver to the steering wheel 11 or the steering actuator 17 is input to the upper steering shaft 12. Since the steering assist force is directly transmitted to the steered wheels W and W, the yaw response of the vehicle (responsiveness of the yawing of the vehicle to the steering) becomes sensitive, and conversely if the torsional rigidity of the steering force transmission path is low Yaw responsiveness tends to be insensitive.

  If a torsion bar type steering torque sensor is used, the torsional rigidity of the torsion bar is the lowest in the steering force transmission path, so the upper limit value of the yaw response of the vehicle is limited by the small spring constant of the torsion bar. Therefore, there is a problem that setting with high yaw response cannot be performed.

On the other hand, when the magnetostrictive torque sensor 34 is employed as in the present embodiment, since there is no member having a small spring constant such as a torsion bar, the upper limit value of the yaw response of the vehicle is set sufficiently high. be able to. If the yaw response of the vehicle is desired to be set low, the rubber bush joints 38, 38 are elastically deformed when a steering force is applied by setting the spring constant of the rubber bush joints 38, 38 small, and the steering is performed. The gear box 16 can be moved relative to the vehicle body 39 in the rack axis direction to reduce the rigidity of the steering force transmission path, thereby making the yaw response insensitive.
Therefore, the yaw response increased as a result of employing the magnetostrictive torque sensor 34 is lowered by adjusting the rubber bush joint 38, 38 spring constant, thereby arbitrarily setting the yaw response of the vehicle in a very wide region. It becomes possible.

  Further, since vibrations transmitted from the wheels W, W to the steering wheel 11 via the steering force transmission path can be absorbed by the rubber bush joints 38, 38 that support the steering gear box 16, the vibration of the steering wheel 11 can be absorbed. The steering feeling can be improved by reducing the above.

  In particular, since the straight portions 42a and 42a are provided in the circumferential region in the rack axial direction of the rubber bush 42 of the rubber bush joints 38 and 38, the amount of deflection δ in the rack axial direction of the rubber bush 42 as shown in FIG. The spring region (slope of the load F with respect to the deflection amount δ) can be set small in the shear region R1 having a small deflection amount δ, and the compression region R2 having a large deflection amount δ. Then, the spring constant (the inclination of the load F with respect to the deflection amount δ) can be set large.

As a result, in the vicinity of the neutrality of the steering wheel 11, even if a temporary disturbance is input from the steered wheels W, W, it corresponds to the shear region R1, so that the disturbance is absorbed by the rubber bush joints 38, 38, and the driver The steering wheel 11 is removed, or the magnetostrictive torque sensor 34 temporarily detects the steering torque due to the disturbance, and the motor 33 outputs the steering assist force according to the detected steering torque. Can be reduced.
Further, as shown in FIG. 4, in the vicinity of the neutrality of the steering wheel 11, the characteristics of the amount of deflection δ and the load F in the rack axial direction of the rubber bush 42 are in the shear region R1. Accordingly, the amount of deflection δ with respect to the change in the load F to the rubber bush 42 increases, so that even if there is a slight input to the steering wheel 11 by the driver in the driving state near the neutral of the steering wheel 11, the rack shaft Since the load generated in the direction is absorbed by the rubber bush 42, the steered wheels W and W are not steered. That is, it is possible to ensure stability when going straight ahead.

  When the driver rotates the steering wheel 11, it corresponds to the compression region R2, so that the electric power steering device outputs the steering assist force with high yaw response.

  Further, conventionally, in a steering system of a vehicle, a rigid element that can be bent to some extent by receiving a load due to an operation of the steering wheel 11 (here, “bend” includes “twist”), For example, since the torsion bar in the conventional torsion bar type torque sensor is included, when the steering wheel 11 is turned in the turning direction (hereinafter referred to as “cutting operation”), the bending thereof may be bent. There is a characteristic that the yaw response of the vehicle with respect to the operation of the steering wheel 11 is improved because the rigid element that can bend is completely bent within a possible range. Such characteristics of the steering system of a vehicle are preferred by drivers who are familiar with driving a vehicle.

On the other hand, the steering system using the magnetostrictive torque sensor 34 has high rigidity, and even when the steering wheel 11 is turned, the amount of twist of the upper steering shaft 12 is small. The change in yaw response according to the change is reduced, and the yaw response is linearly felt accordingly. As a result, there is a possibility that the driver who has become a conventional steering system vehicle may feel unsatisfactory.
According to the present embodiment, the characteristic of the steering system that produces a change in yaw response according to the change in the cut amount can be obtained. A ring can be given, and a sense of incongruity with a conventional vehicle can be eliminated.

As mentioned above, although embodiment of this invention was described, this invention can perform a various design change in the range which does not deviate from the summary. FIG. 7 is a third embodiment of the rubber bush in FIG.
For example, as shown in FIG. 7, the rubber bush 42 has a substantially annular shape, and the direction in which the steering gear box 16 of the circumferential direction portion moves relative to the vehicle body 39, that is, the circumferential direction in the rack axis direction. A pair of straight portions (space portions) 42a and 42a having a predetermined gap width E1 in the direction area are provided, and circumferential recesses 42a ₁ and 42a ₁ are provided at both ends in the circumferential direction of the straight portion 42a.

And the total thickness of the thickness E2A of the rubber bush 42 on the outer peripheral side of the curled portion 42a and the thickness E2B of the rubber bush 42 on the inner peripheral side of the curled portion 42a is the same as that in the rubber bush 42 of the first and second embodiments. The thickness is the same as E2 (E2 = E2A + E2B).
Even with such a shape of the rubber bush 42, the same deflection amount δ-load F characteristic as the rubber bush 42 of the first and second embodiments can be realized.
Further, by providing the recessed portions 42a ₁ and 42a ₁ , no concentrated stress is applied to the end portion in the circumferential direction of the straight portion 42a, so that cracks can be prevented from occurring early, and the durability of the rubber bush 42 is improved. improves. Moreover, peeling from the outer cylinder 40 in the rubber bush 42 of the first embodiment can be prevented more reliably.

  Further, in this embodiment, the steering actuator 17 is provided on the upper steering shaft 12, but it can be provided at any part of the steering force transmission path.

DESCRIPTION OF SYMBOLS 11 Steering wheel 12 Upper steering shaft 14 Lower steering shaft 16 Steering gear box 17 Steering actuator 18 Rack tooth 19 Rack shaft 20 Pinion gear 21 Pinion shaft 24 Housing 27 Housing 34 Magnetostrictive torque sensor 38 Rubber bush joint 39 Body 39a Mounting member 40 Outer cylinder 41 Inner cylinder 42 Rubber bush (elastic body)
42a Straight part (gap, space)
42a ₁ depression 42a ₂ adhesion end 42b, 42c region 71 rubber bush joint arm 71a mounting hole W steered wheel

Claims (4)

An electric power steering system in which a magnetostrictive torque sensor is arranged in a steering force transmission path from a steering wheel to a steered wheel, and a steering actuator is driven according to the steering torque detected by the magnetostrictive torque sensor to assist a driver's steering operation. In the device
A vehicle body support portion that supports a steering gear box disposed between the steering wheel and the steered wheel to the vehicle body via an elastic body having a smaller spring constant than a magnetostrictive torque sensor,
The elastic body generates a load in a direction opposite to the direction of the relative movement according to a relative movement amount of the steering gear box relative to the vehicle body, and an increase amount of the load with respect to the relative movement amount. The electric power steering apparatus is characterized in that the inclination of is greater when the relative movement is equal to or greater than the predetermined value than when the relative movement is equal to or less than a predetermined value. The vehicle body support portion includes a rubber bush joint including an outer cylinder, an inner cylinder disposed on a radially inner side of the outer cylinder, and the elastic body between the outer cylinder and the inner cylinder. ,
The outer cylinder is fitted into a hole provided in the steering gear box, and the inner cylinder is supported by the vehicle body with a bolt,
The electric power steering apparatus according to claim 1, wherein the elastic body has a predetermined gap between the elastic body and the outer cylinder in at least a part of an outer peripheral portion thereof.   The electric power steering apparatus according to claim 2, wherein the predetermined gap is provided in a circumferential region in a direction in which the steering gear box moves relative to the vehicle body. The vehicle body support portion includes a rubber bush joint including an outer cylinder, an inner cylinder disposed on a radially inner side of the outer cylinder, and the elastic body between the outer cylinder and the inner cylinder. ,
The outer cylinder is fitted into a hole provided in the steering gear box, and the inner cylinder is supported by the vehicle body with a bolt,
The elastic body has a substantially annular shape, and a space portion having a predetermined gap is provided in a circumferential region in a direction in which the steering gear box moves relative to the vehicle body in a circumferential portion thereof. The electric power steering apparatus according to claim 1, wherein

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