JP2003002214A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a detection of torque of high accuracy and a stable steering assistance based on this result by eliminating an influence imparted to a torque sensor provided on a midway of a steering shaft by applied force at the time of mounting a housing of the steering shaft to a car body. SOLUTION: A bearing 12 internally fitted to a housing 2 of the steering shaft 1 and supporting the steering shaft 1 at a position apart from the torque sensor 3 is positioned in a longitudinal direction of the shaft by a pair of snap rings 7a, 7b fitted to corresponding positions on the steering shaft 1 and resiliently contacted with both sides of the bearing 12.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering apparatus using an electric motor as a source of a steering assist force. 2. Description of the Related Art A steering assist motor is controlled based on a result of detection of a steering torque applied to a steering wheel (steering wheel) for a steering operation, and the rotational force of the motor is applied to a steering mechanism. In an electric power steering apparatus configured to assist steering, it is necessary to detect a steering torque applied to a steering wheel to use the drive control of the motor, and this detection is performed by a steering that connects a steering wheel to a steering mechanism. It is performed by a torque sensor configured in the middle of the shaft. [0003] This type of torque sensor has been put to practical use in various configurations, and one of them is a torque sensor disclosed in Japanese Patent Publication No. 7-214336 by the present applicant. . This torque sensor is configured such that the steering shaft is divided into an input shaft on the steering wheel side and an output shaft on the steering mechanism side, and these are coaxially connected via a small-diameter torsion bar, and the operation of the steering torque is controlled. Occasionally, a relative angular displacement is generated between the input shaft and the output shaft in accordance with the torsion of the torsion bar, and each of the cylindrical members is externally fitted and fixed near a connection portion between the input shaft and the output shaft. Then, a plurality of teeth are formed so that circumferential positions thereof correspond to end faces of these cylindrical bodies facing each other with a predetermined gap therebetween, and a detection coil is arranged so as to surround a facing portion of these teeth from the outside. When a coil current is supplied to the detection coil, a magnetic circuit passing through the opposing portion of the tooth is formed. [0004] With the above arrangement, when a relative angular displacement occurs between the input shaft and the output shaft due to the action of the steering torque, the facing relationship of the teeth on the end faces of the cylindrical body fitted to both shafts changes. Since the magnetic resistance of the magnetic circuit increases or decreases according to this change, the steering torque can be detected by extracting the impedance change of the detection coil as an output. FIG. 4 is an explanatory view of a state in which a steering shaft of an electric power steering apparatus having the above-described torque sensor is mounted on a vehicle. In this drawing, a steering shaft 1 is rotatably supported inside a cylindrical housing 2.
The housing 2 is supported on the lower surface of the dashboard D of the vehicle via fixing brackets (upper bracket 20 and lower bracket 21) provided near the middle and lower ends of the housing 2, respectively. The torque sensor 3 is formed in the lower half of the housing 2 as shown by a broken line in the figure. The steering shaft 1 is provided with bearings 10 and 11 on both sides of the torque sensor 3 and the torque sensor 3. With the bearing 12 at a position away from the upper part,
It is supported inside the housing 2. The upper and lower ends of the steering shaft 1 protrude outside the housing 2, the steering wheel 4 is fitted to the upper protruding end, and the lower protruding end is connected to a steering mechanism (not shown) via a universal joint 5. Are linked. With the above configuration, the rotation operation of the steering wheel 4 for steering is transmitted to the steering mechanism via the steering shaft 1, and the steering is performed by the operation of the steering mechanism. At this time, the steering torque applied to the steering shaft 1 Is the torque sensor 3
Is detected by A motor M for assisting steering is mounted outside the housing 2 at a position lower than the components of the torque sensor 3. The motor M is driven to rotate based on the detection result of the steering torque by the torque sensor 3, and this rotation is performed by a reduction mechanism configured at a corresponding position inside the housing 2.
The speed is reduced by 13 and transmitted to the steering shaft 1 to assist the steering performed as described above. The upper bracket 20 for supporting the upper portion of the housing 2 is a tilt bracket for supporting the steering shaft 1 inside the housing 2 in a tilt-adjustable manner. This adjustment is performed by operating the tilt lever 22 to tighten the upper bracket 20. , And a vertical force is applied to the steering wheel 4 at the upper end of the steering shaft 1 to swing the housing 2 around the support portion of the lower bracket 21 as a pivot, whereby the tilt angle (tilt angle) of the housing 2 and the steering shaft 1 is increased. Angle) is changed, and the tilt lever 22 is tightened. The upper bracket 20 is a breakout bracket which is detached from its fixed position by the action of a predetermined external force applied downward in the axial direction of the steering shaft 1 and the housing 2. Further, the housing 2 and the steering shaft 1 inside the housing 2 are telescopically contracted between a support portion of the upper bracket 20 and a position where the torque sensor 3 is provided by a predetermined external force applied downward in the axial direction. An energy absorbing section 6 is provided. With this configuration, the energy of the secondary collision in which the driver collides with the steering wheel 4 due to the inertia at the time of the collision of the vehicle can be absorbed by the detachment of the upper bracket 20 and the shortening of the energy absorbing portion 6, so that the driver can be absorbed. The added damage is greatly reduced. FIG. 4B shows a state before the steering shaft 1 is mounted as described above, and the steering shaft 1 is mounted on an upper portion provided in the housing 2. The bracket 20 and the lower bracket 21 are positioned with respect to each of the fixed seats D ₁ and D ₂ provided on the lower surface of the dashboard D. The inserted fixing bolt (not shown) is connected to the fixing seat D ₁ ,
D ₂ each to provided bolt holes is realized by tightening (not shown). [0011] To the attachment satisfactorily performed, the axial pitch P between the upper bracket 20 and lower bracket 21, in the same direction pitch P ₀ between the fixed seat D _1, D ₂ in the vehicle Correct alignment is required. However, the axial pitch P on the side of the housing 2 depends on various types of components added after the components such as the steering shaft 1, the torque sensor 3 and the steering assist motor M are assembled, and before they are carried into an actual vehicle assembly line. Deviation is likely to occur due to the action of external force, and similarly, the pitch P between the fixed seats D ₁ and D ₂ on the side of the actual vehicle
₀ may be out of order due to the action of external force inevitably applied on the assembly line, and as shown in FIG. 4B, the axial pitch P between the brackets 20 and 21 and the fixed seats D ₁ and D ₂ sometimes mounting is made with the difference occurs between the same direction pitch P _0. When such mounting is performed, a tensile force or a compressive force is applied to the housing 2 and the steering shaft 1 supported therein, and these are the weakest parts of the entire steering shaft 1, That is, the torsion bar concentrates on the torsion bar of the torque sensor 3, and the torsion bar expands and contracts.
As a result, as described above, there is a problem that the gap of the opposed portion of the cylindrical body surrounded by the detection coil changes, and the output of the center point initially set in the assembling stage cannot be obtained. An error occurs in the torque detected by the torque sensor 3, and there is a possibility that steering assistance based on this detected torque cannot be performed with high accuracy. Furthermore, when the steering shaft 1 is configured to be tilt adjustment as described above, the above-mentioned mounting of the housing 2, the pitch P, the line to change the tilt angle in order to eliminate the difference between P ₀ At this time, a bending force is applied to the housing 2 and the steering shaft 1 by the fastening of the fixing bolt, and the torsion bar where the bending force is concentrated is bent and deformed, and the output characteristic of the torque sensor 3 is generally changed. And the steering assist based on the torque detected by the torque sensor 3 may not be properly performed. The present invention has been made in view of such circumstances, and supports a steering shaft inside a housing so as to be movable in a predetermined length range in an axial direction, and when the housing is mounted on a vehicle body, the steering shaft is mounted on the steering shaft. Tensile force applied to the housing and steering shaft,
It is an object of the present invention to provide an electric power steering device capable of absorbing a compressive force or a bending force by movement of a support portion, eliminating an influence on a torque sensor, and stably performing high-accuracy steering assistance. An electric power steering apparatus according to the present invention includes a steering shaft which is rotatably supported inside a housing having a bracket for fixing to a vehicle body. An electric power steering device including a torque sensor that detects a steering torque applied to a shaft,
Bearings fixed inside the housing and supporting the steering shaft at a position distant from the torque sensor are respectively fitted to corresponding portions of the steering shaft by a pair of retaining rings elastically contacting both sides of the bearing. Are positioned in the axial direction. In the present invention, the bearing which is fixedly fitted in the housing and supports the steering shaft is supported by a pair of retaining rings which are elastically contacted on both sides of the bearing, and the steering with respect to the housing is limited within the range of elastic deformation of these retaining rings. The shaft can be moved in the axial direction, and this movement absorbs a tensile force, a compressive force, or a bending force applied to the steering shaft when the housing is mounted on the vehicle body, thereby eliminating the influence on the torque sensor. In addition, the retaining ring is supported by a bearing remote from the torque sensor to secure a sufficient absorption length. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings showing the embodiments. FIG. 1 is a longitudinal sectional view of a main part of an electric power steering device according to the present invention. In the figure, reference numeral 1 denotes a steering shaft.
The housing 2 is rotatably supported inside a cylindrical housing 2. An upper bracket 20 and a lower bracket 21 for fixing to a vehicle body (not shown) are provided at a middle portion and a lower end portion (left end portion in the figure) of the housing 2. The housing 2 and the steering shaft 1 Via a bracket 20 and a lower bracket 21, it is supported on a predetermined portion of the vehicle body such as the lower surface of the dashboard D (see FIG. 4). The steering shaft 1 includes a hollow upper shaft 1a protruding from one side of the housing 2 to the outside of a suitable length, a solid intermediate shaft 1b fitted to the other end of the upper shaft 1a, and the other of the intermediate shaft 1b. It has a hollow input shaft 1c connected to the end, and an output shaft 1d connected to the lower end of the input shaft 1c and protruding a suitable length to the outside of the other side of the housing 2. A steering wheel (steering wheel) 4 is fitted and fixed to the protruding end of the upper shaft 1a toward the front end as shown by a two-dot chain line in the drawing. It is connected to a steering mechanism (not shown) via a universal joint 5 which is partially shown. The upper shaft 1a and the intermediate shaft 1b are press-fitted into the lower end of the former by an appropriate length through the upper end of the latter via a sleeve 14 made of a resin material, and when an axial force exceeding a predetermined limit is applied, The sleeve 14 is integrated to be telescopically shrinkable with the sliding resistance of the sleeve 14. Similarly, the input shaft 1c and the output shaft 1d are connected to a small diameter torsion bar 15 inserted through the former hollow portion.
And the intermediate shaft 1b is coaxially connected with the intermediate shaft 1b.A connecting portion between the input shaft 1c and the output shaft 1d is provided with a steering torque applied to the steering shaft 1 by the action of the steering torque. The torque sensor 3 is configured to detect a relative displacement generated between the two shafts 1c and 1d in response to the torsion of the torsion bar 15 as a medium. As disclosed in Japanese Patent Publication No. 7-214336 filed by the present applicant, the torque sensor 3 is provided with the input shaft.
Detection cylinders 30 and 31 each having a plurality of teeth formed so as to fit in the vicinity of the connection portion of the output shaft 1c and the output shaft 1d, and to have a circumferential position corresponding to an opposing end face opposed with a predetermined gap therebetween.
And a detection coil 32 surrounding these opposing portions from the outside. When a coil current is applied to the detection coil 32, a magnetic circuit passing through the opposing portions of the teeth is formed. With this configuration, when a relative angular displacement occurs between the input shaft 1c and the output shaft 1d, the detection tube 3 fitted to both shafts
Since the opposing relationship of the teeth on the end faces of 0 and 31 changes, and the magnetic resistance of the magnetic circuit increases and decreases in accordance with this change, the impedance change of the detection coil 32 is taken out as an output to cause the relative angular displacement. Steering torque can be detected. With the above configuration, the steering wheel 4 for steering is
Is transmitted to the steering mechanism via the steering shaft 1, and the steering is performed by the operation of the steering mechanism.
The steering torque applied to the motor is detected by the torque sensor 3. The housing 2 supporting the steering shaft 1 corresponds to the upper shaft 1a and the intermediate shaft 1b of the steering shaft 1, respectively, and is connected to the lower ends of the upper housing 2a, the intermediate housing 2b, and the intermediate housing 2b, both of which form a tubular shape. A sensor housing 2c for accommodating the torque sensor 3 and a motor housing 2d connected to a lower end of the sensor housing 2c and supporting a steering assist motor M outside the sensor housing 2c are provided. The upper housing 2a and the intermediate housing 2b are press-fitted into the lower end of the former with the upper end of the latter at an appropriate length, and, like the upper shaft 1a and the intermediate shaft 1b of the steering shaft 1, in the axial direction exceeding a predetermined limit. It is integrated in a telescopic manner so that it can be contracted when a force is applied, and the energy of a secondary collision in which the driver collides with the steering wheel 4 due to the inertia when the vehicle collides is transmitted to the upper shaft.
An energy absorbing portion is configured to be absorbed by shortening of the intermediate shaft 1a and the intermediate shaft 1b and shortening of the upper housing 2a and the intermediate housing 2b. The upper bracket 20 supporting the upper part of the housing 2 is fixed to the middle of the upper housing 2a as described above. The upper bracket 20 is configured as a known breakout bracket that separates from a fixed position on the vehicle by the acting force of the steering shaft 1 and the housing 2 in the axial direction, and the upper bracket 20 acts in synergy with the shortening of the energy absorbing portion. The energy of the next collision is absorbed to reduce the damage to the driver. On the other hand, a lower bracket 21 for supporting a lower portion of the housing 2 is fixed to a lower end of the motor housing 2d and is swingable about a substantially horizontal pivot inserted through an insertion hole 23 shown in the drawing. It is pivotally supported on the attachment to the vehicle. The upper bracket 20 is a tilt bracket that supports the housing 2 and the steering shaft 1 in a tilt-adjustable manner. The tilt adjustment is performed by tightening the upper bracket 20 by operating a tilt lever 22 indicated by a two-dot chain line in the drawing. , And a vertical force is applied to the steering wheel 4 at the upper end of the steering shaft 1 to swing the housing 2 about the support of the lower bracket 21 as a pivot.
This is realized by changing the tilt angle (tilt angle) of the camera and tightening the tilt lever 22. The output shaft of the steering assist motor M mounted outside the motor housing 2d extends inside the motor housing 2d at a position away from the axis of the steering shaft 1 so as to be orthogonal to the axis. A worm 13a is fitted to the extension. A worm wheel 13b is externally fitted and fixed to a middle portion of the output shaft 1d supported inside the motor housing 2d, and is meshed with the worm 13a. The motor M is driven to rotate based on the result of the detection of the steering torque by the torque sensor 3. The rotation is reduced by a speed reduction mechanism comprising a worm 13a and a worm wheel 13b and transmitted to the output shaft 1d. ,
The steering is transmitted to the steering mechanism via the universal joint 5 at the lower end of the output shaft 1d, and the steering performed by the operation of the steering mechanism is assisted. In the electric power steering apparatus according to the present invention having the above-described structure, the steering shaft 1 is arranged as shown in FIG.
As shown in the conventional electric power steering system shown in FIG. 1, the bearings 10 and 11 on both sides of the torque sensor 3 and the bearing 12 located at a position separated from the torque sensor 3 are supported inside the housing 2. FIG. 2 is an enlarged cross-sectional view of the vicinity of the support portion at a position apart from the torque sensor 3 by the bearing 12, and a feature of the electric power steering apparatus according to the present invention lies in the configuration of the support portion. As shown in FIG. 2, the bearing 12 includes an upper housing
The outer ring is a ball bearing fitted inside 2a, and its outer ring is restrained from both sides by caulking the peripheral wall of the upper housing 2a, and is fixed so as not to move in the axial direction. The inner ring of the bearing 12 is fitted around the upper shaft 1a. On both sides of the inner ring of the bearing 12, engagement grooves 70a, 70b are formed around corresponding positions of the upper shaft 1a.
The retaining rings 7a and 7b engaged with the shafts are respectively brought into contact with each other, and are positioned in the axial direction by the retaining rings 7a and 7b. As shown in the figure, the retaining rings 7a and 7b are annular leaf springs in which the space between the inner peripheral edge and the outer peripheral edge is inclined to one side in the axial direction, and is elastically deformable by the acting force in the axial direction. The respective outer peripheral edges are opposed to the bearing 12 so as to be engaged with the respective engagement grooves 70a and 70b, and the inner peripheral edges are supported by end walls of the engagement grooves 70a and 70b. The outer peripheral edge is attached to the 12 end faces with elastic contact. With the above configuration, the bearing 12 is positioned in the axial direction of the upper shaft 1a by the spring force of the retaining rings 7a and 7b elastically contacting both surfaces, and is positioned by the caulking with respect to the upper housing 2a. This serves to support the upper shaft 1a in the upper housing 2a. As shown in FIG. 4, the steering shaft 1 and the housing 2 having the above-described support structure are connected to the upper part of the dashboard D with respect to the respective fixed seats D ₁ and D ₂ provided on the lower surface of the dashboard D. The bracket 20 and the lower bracket 21 are aligned and bolted to each other for mounting. In this mounting, as described above, the mounting pitch P between the brackets 20 and 21 and the distance between the fixed seats D ₁ and D _{2 are set.} mounting there is a difference between the pitch P _0, there is that the bolt tensile force to the housing 2 after stopping or compression force is applied. FIG. 3 is an explanatory view of the operation of the support section shown in FIG. 2, and shows the state of the support section by the bearing 12 when a tensile force and a compressive force are applied due to the difference in the mounting pitch as described above. I have. FIG. 3A shows the state shown in FIG. 4B, that is, the mounting pitch P on the brackets 20 and 21 side.
3B is larger than the mounting pitch P ₀ on the fixed seats D ₁ and D ₂ , and shows a state in which a tensile force is applied to the housing 2. FIG. 3B shows the mounting pitch P on the brackets 20 and 21. Is the mounting pitch P _{0 of the} fixed seats D ₁ and D _2.
2 shows a state in which a compressive force is applied to the housing 2. In FIG. 3 (a), the housing 2 (upper housing 2a) moves toward the opening side together with the bearing 12 fitted and fixed thereto by the action of the tensile force indicated by the arrow in the figure. I do. At this time, the steering shaft 1 (upper shaft 1a)
On the side of the bearing, a retaining ring 7a elastically contacting the same end face of the bearing 12 supports the end wall of the engagement groove 70a,
It can be deformed until it takes the form shown in figure a, which absorbs all or most of said tensile force. Therefore, the pulling force introduced to the steering shaft 1 is
At or near zero, the pulling force applied to the torque sensor 3 formed in the lower half of the steering shaft 1 is greatly reduced, and the extension of the torsion bar 15 can be suppressed to a low level. The occurrence of an output error of the torque sensor 3 due to the extension can be effectively reduced. In FIG. 3 (b), the housing 2 (upper housing 2a) is moved toward the inner rear side together with the bearing 12 fitted and fixed thereto by the action of the compressive force indicated by the arrow in the figure. Moving. At this time, the steering shaft 1 (upper shaft 1a)
The retaining ring 7b, which resiliently contacts the end surface of the bearing 12 on the same side, can be deformed until it becomes the illustrated form along the end wall of the engaging groove 70b, and this deformation causes As a result of absorbing all or most of the force, the influence on the torque sensor 3 formed in the lower half of the steering shaft 1 is minimized, and the occurrence of output errors of the torque sensor 3 is effectively reduced. The steering assist described above based on the detected torque can be performed with high accuracy. Further, the retaining ring 7a or 7b deformed as shown in FIG. 3 (a) or FIG. 3 (b) can withstand high strength against the axial force applied in this state. Therefore, the shortening of the steering shaft 1 and the housing 2 for energy absorption at the time of the secondary collision described above is performed in a state in which the steering shaft 1 and the housing 2 are firmly integrated, and the desired energy absorbing ability can be stably exhibited. . The retaining rings 7a, 7a,
7b is not limited to the annular leaf spring shown in FIGS. 2 and 3, but may be any as long as it can be elastically deformed by the axially acting force.
For example, it is also possible to use other types of retaining rings 7a and 7b such as a wave washer obtained by shaping a plate material bent in a wave shape into an annular shape. As described above in detail, in the electric power steering apparatus according to the present invention, the bearing which is fixed to the inside of the housing and supports the steering shaft is supported by a pair of retaining rings which are elastically contacted on both sides of the bearing. Therefore, within the range of elastic deformation of these retaining rings, movement of the steering shaft with respect to the housing in the axial direction is permitted, and the acting force applied to the steering shaft when the housing is mounted on a predetermined portion of the vehicle body is reduced by the torque detected by the torque sensor. The present invention has excellent effects, for example, it is possible to eliminate the influence of the detected torque and stably perform the steering assist based on the detected torque with high accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectional view of a main part of an electric power steering device according to the present invention. FIG. 2 is an enlarged cross-sectional view of the vicinity of a support portion of a steering shaft at a position away from a torque sensor. FIG. 3 is an operation explanatory view of a support section shown in FIG. 2; FIG. 4 is an explanatory diagram of a state in which a steering shaft of the electric power steering device is mounted on a vehicle. [Description of Signs] 1 Steering shaft 1a Upper shaft 1b Intermediate shaft 1c Input shaft 1d Output shaft 2 Input shaft 2a Upper housing 2b Intermediate housing 2c Sensor housing 2d Motor housing 3 Torque sensor 4 Steering wheel 7a Retaining ring 7b Retaining ring 12 Bearing 15 Torsion bar

Claims (1)

Claims: 1. A torque sensor for detecting a steering torque applied to a steering shaft is provided in a middle portion of the steering shaft rotatably supported inside a housing having a bracket for fixing to a vehicle body. An electric power steering apparatus comprising: a bearing that is internally fitted and fixed to the housing and that supports the steering shaft at a position distant from the torque sensor; each of the bearings is fitted to a corresponding portion of the steering shaft; An electric power steering device characterized by being positioned in the axial direction by a pair of snap rings that elastically contact.