JPH06211143A - Electric actuator of four-wheel steering system - Google Patents

Abstract

PURPOSE:To provide an electric actuator having a mechanical fail-safe mechanism to hold a rear wheel steering angle in a specific angle scope forcibly even when a trouble is generated in a four-steering system. CONSTITUTION:The rotating operation of a motor 30 is converted into the linear operation of a shaft 22 by a ball screw 42, and the rear wheels are steered by the movement of the shaft 22. When the shaft 22 is going to move linearly across a specific shaft moving scope corresponding to the clearance between a moving body 51 and a lock pin 52 at a neutral position of the shaft, the moving body 51 is abutted to the lock pin 52, and the further movement of the shaft is blocked.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric actuator for a four-wheel steering system, and more particularly to an actuator of this type having a mechanical fail-safe mechanism.

[0002]

2. Description of the Related Art It is known to equip a vehicle with a four-wheel steering (4WS) system that steers the rear wheels while steering the front wheels to improve the steering stability of the vehicle. Typically,
When the vehicle runs at low speed, the anti-phase control that bends the front and rear wheels in the opposite direction is performed to improve the maneuverability, and the in-phase control that bends the front and rear wheels in the same direction is performed when driving at medium and high speeds to improve the running stability.

There are various methods of giving a turning angle to the rear wheels, for example, a mechanical type in which a rear wheel steering rack and pinion mechanism incorporated in a front steering gear box and a rear steering gear box are connected via a center shaft. A 4WS system is known, and a rear steering gear box includes an eccentric shaft connected to a center shaft, a planetary gear connected to the eccentric shaft, and an internal gear that meshes with the planetary gear. This 4WS system causes the planetary gear to revolve along the internal gear as the center shaft rotates while rotating in the direction opposite to the eccentric shaft, and further, via a stroke rod connected to another eccentric shaft attached to the planetary gear, Steer the rear wheels. Although this mechanical 4WS system has advantages such as low cost, it steers the front wheels and the rear wheels at the same time as the steering angle proportional to the front wheel steering angle. I can't do it with a delay, etc.
There is a lack of flexibility in steering the rear wheels.

Therefore, conventionally, a hydraulic or electric actuator for steering the rear wheels is computer-controlled in accordance with a target rear wheel steering angle generated by a control unit based on the front wheel steering angle, the vehicle speed, etc. A 4WS system has been proposed in which the timing, the size of the rear wheel steering angle, and the like can be optimized. The conventional electric actuator used in the electric 4WS system typically includes a rear wheel steering shaft connected to the knuckle arms of the left and right rear wheels, a motor electrically connected to the control unit, and a motor. It is equipped with a ball screw for converting rotational movement into linear movement of the shaft and a steering angle sensor for detecting the actual rear wheel steering angle.By applying a drive current to the motor from the control unit, The shaft is linearly moved by the motor in the direction corresponding to the motor rotation direction, and the rear wheels are steered so that the actual rear wheel steering angle becomes the target rear wheel steering angle. The electric actuator further includes a centering spring that biases the rear wheel steering shaft toward the neutral position side. When the drive current supply to the motor is stopped due to a failure of the 4WS system, the centering spring causes the shaft to be neutralized. I try to return it to the position.

[0005]

As described above, the conventional electric actuator has the fail-safe function of forcibly returning the rear wheel steering shaft to the neutral position when the supply of the motor current is stopped. It does not have a sufficient fail-safe function for supplying excessive motor current. That is, in the conventional electric 4WS system, although the control unit and the rudder angle sensor are provided with a plurality of systems and the reliability of the control program is improved, the control unit or the rudder angle sensor malfunctions. There are still fears. Then, if the control unit or the like malfunctions, an excessive current is supplied to the motor, the steering angle of the rear wheels becomes excessive, and the vehicle behaves unexpectedly for the driver. Further, if the shaft is returned to the neutral position from such an excessively steered state by the return spring, the behavior of the vehicle becomes extremely unnatural.

In view of this, the present invention has four wheels equipped with a mechanical fail-safe mechanism that operates so as to force the rear wheel steering angle to fall within a predetermined angle range even if a failure occurs in the four-wheel steering system. An object is to provide an electric actuator of a steering system.

[0007]

SUMMARY OF THE INVENTION According to the present invention, there is provided a shaft for linearly movably supporting the left and right rear wheels, a motor, and a conversion for converting rotational motion of the motor into linear motion of the shaft. In a four-wheel steering system electric actuator having means, a movable body provided integrally with a shaft so as to move integrally with the movable body, and the shaft contacting the movable body when the shaft attempts to linearly move beyond a predetermined shaft movement range. And a rudder angle limiting member arranged to prevent further shaft movement.

Preferably, the rudder angle limiting member is arranged so as to move toward and away from the moving body in a direction orthogonal to the shaft axis, and the moving body and the rudder angle limiting member are located at the approaching position of the rudder angle limiting member. It is provided so that the width of the predetermined shaft movement range is different at a certain time and at a separated position.

[0009]

When the steering handle is rotated, the front wheels are steered, and a drive current is supplied to the motor of the actuator to rotate the motor. The rotational movement of the motor is converted into linear movement of the shaft in a direction corresponding to the motor rotation direction by the conversion means, and the left and right rear wheels are steered by the steering angle corresponding to the shaft movement amount. As long as the four-wheel steering system operates normally, the shaft moves within a predetermined shaft movement range. On the other hand, if some abnormality occurs in the four-wheel steering system and the shaft tries to move linearly beyond the predetermined shaft movement range, the moving body provided on the shaft comes into contact with the steering angle limiting member, so that the further straight line movement of the shaft occurs. Movement is blocked. This prevents the shaft from moving excessively and making the behavior of the vehicle significantly unnatural.

The rudder angle limiting member is movable toward and away from the moving body in a direction orthogonal to the shaft axis, and a predetermined shaft moving range is obtained when the rudder angle limiting member is in the approach position and in the distant position. In a specific aspect of the present invention in which the width of the steering wheel is made different, for example, when the front wheel steering angle is small, the steering angle limiting member is moved to a position close to the moving body and the predetermined shaft moving range is narrowed. On the other hand, when the front wheel steering angle is large, the steering angle limiting member is moved to a position away from the moving body, and the predetermined shaft moving range is widened. That is, the shaft movement range is further optimized according to the front wheel steering angle, and the reliability of the fail safe function is improved.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A vehicle equipped with a four-wheel steering system including an electric actuator according to a first embodiment of the present invention will be described below with reference to FIGS. As shown in FIG. 1, a vehicle includes a hydraulic front wheel power cylinder 1 for steering left and right front wheels FLW, FRW, and left and right rear wheels RL.
Electric actuator 2 for steering W and RRW
And a control unit (ECU) 3 for controlling the operation of the actuator 2. ECU
3 includes a steering wheel angle sensor 5 for detecting a rotation angle of the steering wheel 4, for example, a vehicle speed sensor 6 for detecting a vehicle speed from rotation of an output shaft of a transmission (not shown) connected to an engine (not shown). Various sensors are connected.

Although not shown in detail, the front wheel power cylinder 1 has a power piston and a pair of pressure chambers defined on both sides of the power piston. Both pressure chambers are built in a gear box of the power steering device. It is connected to the oil pump via the steering control valve. The steering control valve supplies oil to one of the two power cylinder pressure chambers corresponding to the steering direction of the steering wheel, thereby moving the power piston in the direction corresponding to the steering direction, and the left and right front wheels operated by the steering wheel. It is designed to help steer the car.

As shown in FIG. 2, the electric actuator 2
Includes a casing 21 arranged at the rear of the vehicle and a shaft 22 arranged inside the casing along the axial direction of the casing. The shaft 22 is linearly movable to the left and right rear wheels, and has bearings 2a, 2b. Through the casing 21
It is supported by. Both ends of the shaft 22 penetrate the casing end surface and extend to the outside of the casing, and the joint 2
The left and right tie rods 27, 28 are connected via 5, 26, respectively. The connecting portion between the shaft and the tie rod is surrounded by the bellows 29, and the both tie rods 27 and 28 are
The knuckle arms (not shown) of the left and right rear wheels are respectively connected.

The electric actuator 2 further includes a motor 30, which is supported by the casing 21 via bearings 23 and 24 and a permanent magnet 32 which is fixed to the inner surface of the casing so as to face the rotor 31.
Includes and. The rotor 31 is connected to the ECU 3 via a commutator 33 adjacent to the rotor and rotating with the rotor, a brush (not shown) electrically slidably connected to the commutator 33, and a wiring 34 connected to the brush. It is connected to a driver circuit (not shown) that operates under the control of (1) and rotates about the shaft axis when a drive current is supplied from the driver circuit. Further, a ball screw 42 that meshes with a ball nut 41 supported by the casing 21 via a bearing 23 is formed on the shaft 22 on the axially outer side with respect to the rotor 31, and the ball nut and the ball screw are used to rotate the motor. To constitute a linear movement of the shaft 22.

A movable body 51 is fitted and fixed to the intermediate portion of the shaft 22 adjacent to the commutator 33, and on the inner surface of the casing 21, the movable body 51 is opposed to the movable body 51 so as to serve as a steering angle limiting member. An angle limiting lock pin 52 is arranged.
The lock pin 52 includes a shaft portion 52a extending orthogonally to the shaft axis center and an engaging portion 52b integral with the shaft portion 52a.
The outer end of 2a extends through the casing 21 to the outside of the casing. The lock pin 52 is supported by the casing 21 at an outer end of its shaft portion so as to be movable toward and away from the movable body 51. Further, between the lock pin 52 and the casing 21, a spring 53 having one end in contact with the inner surface of the casing and the other end accommodated in an annular groove formed in the lock pin 52 is interposed. The moving body 51 is constantly urged by the spring 53. An inner end of the lock pin engaging portion 52b is formed in a trapezoidal cross section, and a complementary groove 51a is formed on the facing surface of the moving body 51.

The groove 51a of the moving body allows a linear movement of the shaft corresponding to a rear wheel steering angle of, for example, 0.8 degrees from the shaft neutral position when the lock pin 52 takes a position close to the moving body 51. It is formed in a shape and dimension that allows it. In other words, the tip surface of the lock pin 52 is the moving body 5.
The gap defined between the inclined surface of the lock pin engaging portion 52b and the inclined groove surface of the movable body 51 in the state shown in FIG. 2 near the groove bottom surface of No. 1 corresponds to a steering angle of 0.8 degrees. is doing.
Further, the shape and size of the groove 51a of the moving body is such that when the lock pin 52 takes the position farthest from the moving body 51 against the spring force of the spring 53, it moves corresponding to a rear wheel steering angle of 5 degrees, for example. It is set to allow a linear movement of the shaft by a certain amount. The lock pin 52 is designed so as not to deviate from the groove 51a of the moving body even when the lock pin 52 is most separated from the moving body 51.

In FIG. 2, reference numeral 54 indicates a lock pin sensor which is provided on the outer surface of the casing in alignment with the lock pin shaft portion 52a and detects the operating position of the lock pin 52. Reference numeral 55 represents a center pin for accurately determining the axial position of the moving body 51 in the shaft neutral state, and is used for positioning the moving body during assembly or maintenance of the electric actuator.

In connection with the electric actuator 2, 4WS
The system further includes a steering angle responsive drive mechanism for moving the lock pin 52 in a direction orthogonal to the shaft axis. As shown in FIGS. 3 and 4, the drive mechanism 60
Includes a housing 61 that rotatably supports the tip of the steering shaft 4a, a small gear 62a fixed to the tip of the steering shaft, and a large gear 62b that is rotatably supported by the housing 61 and meshes with the small gear 62a. Reference numerals 62a and 62b constitute a reduction gear 62. The crankshaft 63 is eccentrically fixed to one end surface of the large gear 62b with respect to the axis of the large gear, and the annular base end portion of the crank 64 is fitted to the crankshaft 63, and the crank 64 is provided at the tip thereof. Crank pin 6
5, it is pivotally connected to a piston 66.

Further, one end of a wire 68 is connected and fixed to the tip of a piston rod 67 integrated with the piston 66, and the other end of the wire 68 is connected and fixed to the outer end of the shaft portion of the lock pin 52 of the electric actuator 2. ing. Therefore, when the steering wheel 4 rotates, the steering wheel rotating force causes the steering shaft 4a, the reduction gear 62, and the crank mechanisms 63, 6 to rotate.
It is transmitted to the piston 66 through 4, 65 so that the piston 66 slides in a cylinder 70 integrated with the housing 61. The reduction gear 62 and the crank mechanisms 63, 64, 65 suppress the sliding momentum of the piston 66 until the rotation angle of the handle 4 from the handle neutral position exceeds a predetermined angle, for example, 230 degrees, while the handle rotation angle is 230. When the degree is exceeded, the piston sliding momentum is increased. Therefore, when the handle rotation angle exceeds, for example, 230 degrees, the lock pin 52 connected to the piston 66 via the wire 68 resists the spring force of the spring 53 and moves in the direction orthogonal to the shaft axis center, thereby changing the handle angle. As it increases, it gradually moves away from the moving body 51. In FIGS. 3 and 4, reference numeral 71 indicates a spring that constantly urges the piston 66 to the side opposite to the crank mechanism, and the spring 71 prevents hysteresis in steering the rear wheels.

Referring again to FIG. 2, the electric actuator 2 has a motor 3 which is caused by a failure of the 4WS system or the like.
A centering spring 80 for forcibly returning the shaft 22 to the neutral position when the drive current supply to 0 is stopped, and a viscous coupling as a damping means for gently performing the forcible return by the centering spring. And a unit (VCU) 90.

Specifically, the centering spring 80
Is arranged on the side opposite to the motor 30 with respect to the moving body 51 in the axial direction of the shaft, and has a substantially cylindrical stationary spring seat 81 fixed to the inner peripheral surface of the casing and the shaft 2.
It is housed between a movable spring seat 82 having a substantially cylindrical shape, which is fitted and fixed to the stationary spring seat 2 and is movable with respect to the stationary spring seat. The movable spring seat extension 82
a is formed in such a shape that the diameter of the extension portion 82a increases linearly toward the outer side in the axial direction of the shaft.
Actuator 1 arranged so that its tip contacts the outer peripheral surface of 2a
The steering angle sensor 100 having 01 detects the shaft movement position and thus the actual rear wheel steering angle.

The VCU 90 is arranged on the opposite side of the moving body 51 with respect to the motor 30 in the axial direction of the shaft, and is fixed to a plurality of first plates 9 fixed to the inner peripheral surface of the casing 21.
1 and a plurality of second plates (not shown) fixed to a rotating shaft (not shown) inside the VCU and arranged alternately with the first plates, and a viscous fluid such as silicon oil is filled between the plates. Has been done. In the VCU 90, when a rotation speed difference occurs between the first plate and the second plate, the shear resistance of the silicone oil enables torque transmission between the first plate and the second plate. And V
The second plate of the CU 90 is an electromagnetic clutch 110 mounted on the rotating shaft of the VCU 90 and the outer end surface of the ball nut 41.
The ball nut 41 can be rotatably coupled via the. The electromagnetic clutch 110 responds to a control output from the ECU 3, and for example, the ball nut 41 is wound and tightened when the ON operation is performed, while the ball nut 41 is loosened when the OFF operation is performed. That is, the electromagnetic clutch 110
Thus, the rotational coupling between the VCU 90 and the ball nut 41 is established or released.

The operation of the above-configured 4WS system will be described below. When the handle 4 is rotated, the ECU 3
Executes four-wheel steering control according to a control program stored in advance in a built-in memory (not shown). In this four-wheel steering control, the ECU 3 reads output signals representing the front wheel steering angle and the vehicle speed from the steering angle sensor 4 and the vehicle speed sensor 6, respectively, and then refers to the map stored in the internal memory to refer to the front wheel steering. The target rear wheel steering angle according to the angle and the vehicle speed is calculated by a conventionally known method. Preferably, a target rear wheel steering angle is calculated such that the rear wheels are momentarily steered in a reverse phase at the initial stage of turning and then steered in the same phase. Further, as illustrated in FIG. 5, the target rear wheel steering angle is 2 degrees from the steering wheel neutral position.
In the steering wheel angle region up to 30 degrees, for example, a value of 0.8 degrees or less is taken, and in the steering wheel angle area of 230 degrees to 400 degrees, for example, the value is 0.8 degrees to 5 degrees, and more. In the area of the steering wheel angle, for example, the value is 5 degrees or less.

First, the case where the steering wheel angle is less than 230 degrees will be described. In this case, as the handle 4 is rotated, in the drive mechanism 60, the crank pin 6 is passed through the reduction gear 62, the crankshaft 63, and the crank 64.
Although 5 is slightly displaced to the crankshaft side, the crank pin 65 only moves within the dead zone groove 61a provided on the crank mechanism side of the piston 66, and the wire 68 cannot be pulled to the drive mechanism 60 side. As a result, the steering angle limiting lock pin 52 is held at the position shown in FIG. 2, which is close to the bottom surface of the groove 51a of the moving body 51.
A predetermined shaft movement range having a width corresponding to the rear wheel steering angle is set.

The ECU 3 sends a control output corresponding to the target rear wheel steering angle calculated as described above to the driver circuit, whereby a driving current is supplied from the driver circuit to the motor 30 and the rotor 31 of the motor 30 is supplied. Rotates around the shaft axis. Since the ball screw 42 that meshes with the ball nut 41 that can rotate integrally with the rotor 31 is formed on the shaft 22, the shaft 22 moves to the left or right rear wheel side corresponding to the motor rotation direction.
It moves against the spring force of. This allows the shaft 22
The tie rods 27 and 28 connected to both ends of the shaft move in the axial direction of the shaft, and the left and right rear wheels connected to the tie rod are steered. During this period, the ECU 3 feedback-controls the rear wheel steering angle based on the target rear wheel steering angle and the output signal from the steering angle sensor 100 that represents the actual rear wheel steering angle.

When the supply of the drive current from the driver circuit to the motor rotor 31 is cut off due to a failure of the 4WS system or the like during the above-mentioned rear wheel steering, the electromagnetic clutch 110 is turned on under the control of the ECU 3, for example. VCU90
And the rotor 31 are in a rotationally coupled state. At the same time,
The shaft 22 is forcibly returned toward the neutral position by the spring force of the centering spring 80. At this time, the shaft 22 linearly moves to the neutral position side. The second plate group of the VCU 90 is connected to the rotor 3 via the electromagnetic clutch 110.
While the first plate group 91 of the VCU 90 is fixed to the casing 21 while being in the rotationally coupled state with No. 1, a rotational speed difference occurs between the first plate group and the second plate group, and both plate groups are Become capable of transmitting torque to each other via silicone oil. In other words, VCU90
Acts to damp the rotational movement of the rotor 31 and thus the linear movement of the shaft 22. Therefore, VCU90
Under the damping action of, the centering spring 80 forcibly returns the shaft 22 relatively gently, and thereby the left and right rear wheels return to the straight running position gently,
There is no sudden change in vehicle behavior.

On the other hand, when the drive current supplied to the motor rotor 31 becomes excessive due to a failure of the 4WS system or the like during steering of the rear wheels, the shaft 22 moves to the left or right rear wheel side corresponding to the drive current. Trying to move in a large straight line. However, in the region where the steering wheel angle is 230 degrees or less, the lock pin engaging portion 52b is not moved to the moving body 51 as shown in FIG.
Inside the groove 51a. Therefore, when the shaft 22 attempts to move linearly beyond the amount of movement corresponding to the rear wheel steering angle of 0.8 degrees, one groove surface of the moving body 51 fixed to the shaft 22 faces the lock pin engaging portion 52b. Abut the surface,
Further linear movement of the moving body 51 and thus the shaft 22 is prevented.

As described above, even if the motor current supply is cut off or becomes excessive due to a failure of the 4WS system, the mechanical fail-safe mechanism operates to change the behavior of the vehicle. To prevent. Next, the steering wheel angle is 2
A case of 30 degrees to 400 degrees will be described. In this case, as the handle 4 is rotated, the piston 66 of the drive mechanism 60 is displaced toward the crank mechanisms 63 to 65,
The wire 68 is driven by the length corresponding to the steering wheel angle 6
Pull to the 0 side. As a result, the steering angle limiting lock pin 52 is separated from the bottom surface side of the groove 51a of the moving body 51 by the wire pulling length, and a predetermined shaft moving range having a width corresponding to the steering wheel angle is set. That is, the predetermined shaft moving range is ± 0.8 depending on the steering wheel angle of 230 degrees to 400 degrees.
The width is set to correspond to the rear wheel steering angle of 5 to ± 5 degrees. Therefore, when the drive current supplied to the motor rotor 31 becomes excessive due to a failure of the 4WS system or the like during the rear wheel steering, the shaft 22 corresponds to the rear wheel steering angle of 0.8 to 5 degrees. When a linear movement is performed exceeding the movement amount, the moving body 51 abuts on the lock pin 52 and further linear movement of the shaft 22 is blocked. The other operations are similar to those in the case where the steering wheel angle is less than 230 degrees, and thus the description thereof will be omitted.

Next, the case where the steering wheel angle is 400 degrees or more will be described. In this case, the displacement of the piston 66 of the drive mechanism 60 accompanying the rotation operation of the handle 4 causes the wire 6 to move.
8 is pulled toward the drive mechanism 60, the lock pin 52 is separated from the groove 51a of the moving body 51, and a predetermined shaft movement range of a width corresponding to a rear wheel steering angle of ± 5 degrees is set. Therefore, when the drive current supplied to the motor rotor 31 becomes excessive due to a failure of the 4WS system or the like during the rear wheel steering, the shaft 22 exceeds the movement amount corresponding to the rear wheel steering angle of 5 degrees. When the linear movement is attempted, the moving body 51 comes into contact with the lock pin 52 and the further linear movement of the shaft 22 is prevented. The other operations are similar to those in the case where the steering wheel angle is less than 230 degrees, and thus the description thereof will be omitted.

Hereinafter, an electric actuator according to a second embodiment of the present invention will be described with reference to FIGS. 6 to 9. The electric actuator according to the present embodiment is intended to increase the mechanical strength of the steering angle limiting mechanism for restricting the linear movement range of the rear wheel steering shaft. There are major differences in the configurations of the body and the steering angle limiting member.

The electric actuator of this embodiment has the same structure as that shown in FIG.
It has the same configuration as that of the first embodiment shown in FIG. Therefore, in FIG. 6, elements common to the first and second embodiments are designated by the same reference numerals, and detailed description thereof will be omitted. Referring to FIG. 6, the steering angle limiting mechanism of the electric actuator 2 includes a moving body 510 fixed to the shaft 22 and a steering angle limiting lock shaft 520 for limiting the linear movement amount of the moving body and thus the shaft 22. Have

As shown in FIG. 7, the movable body 510 includes first and second movable body half portions each having a semi-cylindrical hole that defines a cylindrical hole into which the shaft 22 is fitted in cooperation with each other. 51
1, 512, both half of the moving body are fixed to the shaft 22 by being clamped together with the shaft 22 sandwiched therebetween. On the other hand, the lock shaft 520
Has a main body portion 521 and a shaft portion 522 integral with the main body portion 521. The shaft portion 522 extends orthogonally to the shaft axis center, and the outer end portion thereof penetrates the casing 21 and extends to the outside of the casing. The lock shaft 520 is supported by the casing 21 so as to be movable toward and away from the moving body 510 at both the outer end portion of the shaft portion 522 and the opposite shaft portion side end portion of the main body portion 521. According to this lock shaft support structure, the mechanical strength of the rudder angle limiting mechanism is increased. Also, the lock shaft 520 and the casing 2
The moving body 510 is provided by the spring 53 interposed between the moving body 510 and
Always urged to the side.

As shown in FIG. 8, the main body portion 521 is formed with an engaging portion 523 having a triangular cross section along its longitudinal axis, and the engaging portion 523 is formed on the second moving body half portion 512. Engagement groove 513 of complementary shape formed, that is, trapezoidal cross section
Is loosely fitted into. In the engaging groove 513, the one side outer end surface 521b of the lock shaft main body 521 is formed in the casing 21.
Is formed in a shape and dimension that allows linear movement of the shaft by a movement amount corresponding to, for example, 0.8 degrees of the rear wheel steering angle from the neutral position of the shaft when the position is in contact with the facing inner end surface. . In other words, the end surface of the lock shaft engaging portion 523 and the second moving body half portion 51 when the lock shaft 520 is close to the moving body 510 and shown in FIGS. 6 and 7.
The gap defined between the two engagement groove defining surfaces corresponds to a steering angle of 0.8 degrees. Further, the shape and size of the engaging groove 513 is set such that when the lock shaft 520 takes a position away from the moving body 510 against the spring force of the spring 53, the amount of movement corresponding to a rear wheel steering angle of 5 degrees, for example. It is set to allow linear shaft movement.

Next, the operation of the steering angle limiting mechanism will be briefly described. The wire 68 is driven by the drive mechanism 60 shown in FIGS.
When the lock shaft 520 is pulled through the lock shaft 520 and moves away from the moving body 510, the lock shaft engaging portion having a triangular cross section loosely fitted in the engaging groove 513 having a trapezoidal cross section of the moving body 510. 523 is the engaging groove 51
3 moves backward, and the inclined surface of the engaging portion 523 and the moving body 5
The gap with the engagement groove defining surface of 10 is widened. That is, the width of the predetermined shaft movement range is variably set according to the amount of separation movement of the lock shaft 520 accompanying the handle operation. As is apparent from FIGS. 8 and 9, the lock shaft 520 does not deviate from the engagement groove 513 even when the lock shaft is farthest from the moving body 510.

Since the other operations of this embodiment are substantially the same as those of the first embodiment, the description of the operation will be omitted. The electric actuator of the present invention is not limited to the above-mentioned first and second embodiments, but can be variously modified. For example, in the above both embodiments, the case where the electric actuator of the present invention is installed in a 4WS vehicle having a hydraulic front wheel power cylinder has been described. However, the present invention is a vehicle in which the electric actuator steers the front wheels. Can be equipped with. Further, in both of the above embodiments, the rear wheel steering angle is feedback-controlled based on the target rear wheel steering angle and the actual rear wheel steering angle detected by the steering angle sensor 100, but the present invention is not limited to this. Instead, it can also be applied to a 4WS system that performs open-loop control of the rear wheel steering angle.

In both of the above embodiments, the moving bodies 52 and 520 as the shaft side elements of the steering angle limiting mechanism are provided separately from the shaft 22, but the moving bodies may be provided integrally with the shaft. That is, instead of the shaft 22 of the embodiment, a shaft that also functions as a moving body may be used. Further, the ball nut 41 serving as a conversion unit converts the rotational movement of the motor 30.
A linear motor having the function of the conversion means can be used instead of the structure in which the linear motion is converted by the ball screw 42.

Further, in both of the above embodiments, the electric actuator is equipped with the VCU 90 as a damping means for reducing the forced returning speed of the centering spring 80 to the neutral position of the shaft 22, but the damping means is not an essential element and is eliminated. It is possible. Also, as the attenuation means, VCU
Instead, various mechanisms such as a mechanism including a rotary friction plate as a main component can be used.

[0038]

As described above, the shaft that is linearly supported so as to steer the left and right rear wheels, the motor, and the converting means for converting the rotational movement of the shaft by the motor into the linear movement of the shaft. The present invention relates to an electric actuator of a four-wheel steering system including: a movable body provided on a shaft so as to be movable integrally therewith; and a movable body when the shaft attempts to move linearly beyond a predetermined shaft movement range. Since the steering angle limiting member arranged so as to abut and prevent further shaft movement is provided, the rear wheel steering angle is forcibly kept within a predetermined angle range even when a failure occurs in the four-wheel steering system. A mechanical fail-safe mechanism that operates in this manner is provided to prevent excessive movement of the shaft and significant unnatural behavior of the vehicle.

Preferably, the rudder angle limiting member is arranged so as to move toward and away from the moving body in a direction orthogonal to the shaft axis, and when the moving body and the rudder angle limiting member are in the approaching position. Since the width of the predetermined shaft moving range is made different depending on whether the shaft is in the separated position or not, the shaft moving range is more optimized, for example, according to the front wheel steering angle, and the reliability of the fail safe function is improved. .

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a 4WS vehicle including an electric actuator according to a first embodiment of the present invention.

FIG. 2 is a longitudinal sectional view showing the electric actuator according to the first embodiment of the present invention.

FIG. 3 is a schematic side view showing a steering angle responsive drive mechanism used with the electric actuator of FIG.

FIG. 4 is a schematic plan view of the drive mechanism shown in FIG.

5 is a steering wheel angle-rear wheel steering angle characteristic diagram of a 4WS vehicle equipped with the electric actuator of FIG.

FIG. 6 is a longitudinal sectional view showing an electric actuator according to a second embodiment of the present invention.

7 is a longitudinal sectional view of a steering angle limiting mechanism of the electric actuator shown in FIG.

8 is a longitudinal sectional view of a lock shaft of the steering angle limiting mechanism shown in FIG.

9 is a sectional view of a second half of a moving body of the steering angle limiting mechanism shown in FIG.

[Explanation of symbols]

 1 Front Wheel Power Cylinder 2 Electric Actuator 3 Control Unit (ECU) 4 Handle 5 Steering Angle Sensor 6 Vehicle Speed Sensor 21 Casing 22 Shaft 27, 28 Tie Rod 30 Motor 41 Ball Nut 42 Ball Screw 51 Moving Body 52 Steering Angle Limit Lock Pin 60 Drive Mechanism 64 Crank 66 Piston 68 Wire 80 Centering spring 90 Viscous coupling unit (VCU) 100 Rudder angle sensor 110 Electromagnetic clutch

Front page continuation (72) Inventor Nobuo Momose 5-3-8 Shiba, Minato-ku, Tokyo Within Mitsubishi Motors Corporation (72) Inventor Tadao Tanaka 5-3-8 Shiba, Minato-ku, Tokyo Mitsubishi Motors Corporation Stock In the company

Claims (2)

[Claims] 1. A shaft which is linearly movably supported for steering the left and right rear wheels, a motor, and a conversion means for converting rotational motion of the shaft by the motor into linear motion of the shaft. In an electric actuator of a four-wheel steering system, a moving body provided on the shaft so as to be movable integrally with the shaft, and abutting on the moving body when the shaft attempts to move linearly beyond a predetermined shaft moving range. An electric actuator for a four-wheel steering system, comprising: a steering angle limiting member arranged to prevent the shaft from moving. 2. The rudder angle limiting member is arranged so as to move toward and away from the moving body in a direction orthogonal to a shaft axis, and the moving body and the rudder angle limiting member are the rudder angle limiting member. The electric actuator of the four-wheel steering system according to claim 1, wherein the predetermined shaft movement range is different between when the vehicle is in the approaching position and when the vehicle is in the separating position.