JPH11124045A - Electrically powered steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact electrically powered steering device using a gear with a tooth profile of a special theory. SOLUTION: This device is configured so that it assists with the revolving of a steering shaft via a speed reduction mechanism comprised of an output gear of an electric motor fixed to the shaft. In this case, gears 21 and 22 of the speed reduction mechanism are formed by a spur gear or a helical gear with a tooth profile of special theory, and the speed reduction mechanism is contained in a housing 3 to support the respective gears so that they can rotate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric power steering device for an automobile, and more particularly to an electric power steering device using a spur gear or a helical gear for a speed reduction mechanism.

[0002]

2. Description of the Related Art A power steering device for an automobile is a device for improving the steering performance by reducing the operating force of a steering wheel. Generally, hydraulic power is used. An electric power steering device used is provided.

[0003] In a conventional electric power steering apparatus, the electric motor rotates the steering shaft via a worm gear. This deceleration mechanism
Due to the low torque transmission efficiency of the worm gear (60 to 80
%), If the reduction gear ratio is not changed, a larger motor output torque is required, and as a result, the motor outer diameter is increased. In view of this, there have been provided many motors in which a driving motor is mounted in parallel with a column and a spur gear is used as a speed reduction mechanism (Japanese Utility Model Application Laid-Open Nos. 62-144773 and 58-149255).
Reference).

[0004]

When a spur gear is used,
Since the torque transmission efficiency is high (approximately 95%), the motor output torque is reduced accordingly, and the motor can be made compact. However, this reduction mechanism has a problem in that if the required reduction ratio is to be established in one stage of the motor pinion gear and the gear meshing with the motor pinion gear, the outer diameter of the driven gear becomes large and the compactness is still lacking. Was. Also, 1
If the step structure is abandoned and the intermediate gear is interposed, there is a new problem that the backlash increases and the cost increases (see Japanese Utility Model Laid-Open No. 1-145668).

[0005] Therefore, the present invention seeks to reduce the size of an electric power steering apparatus in which an electric motor and a reduction mechanism are arranged on a steering column having a steering wheel fixed to one end.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides an electric power steering apparatus which assists the rotation of a steering shaft via a reduction mechanism comprising a driven gear fixed to the shaft and an output gear of an electric motor. Wherein the reduction mechanism is formed of a pair of spur gears or helical gears set at a high reduction ratio, and the reduction mechanism is housed in a housing. By forming a reduction mechanism using a spur gear or a helical gear of the above, and by housing this in the housing, the electric motor can be provided close to the housing, so that the electric motor and the reduction mechanism are arranged on the steering column. The compact steering column can be achieved.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. As shown in FIGS. 1 and 2, a housing 3 is fixed by fitting a tubular portion 3 a to the lower end of a lower jacket 2 of a steering column 1, and a steering shaft 5 is rotated via a bearing 4 on the tubular portion 3 a. The steering shaft 5 is freely supported, and the lower end portion of the steering shaft 5 is supported by an end plate 3b via a bearing 4a.
It is fitted to.

[0008] A shaft hole 5a is formed at the lower end of the steering shaft 5, and a torsion bar 6 is inserted into the shaft hole 5a and the upper end thereof is connected by a pin 7. A serration 6a is formed on the outer peripheral surface of the lower end portion of the torsion bar 6, and a shaft 8 having a hole 8a formed on the inner peripheral surface of the serration engaging with the serration 6a is connected thereto.

The end faces of the shaft 8 and the steering shaft 5 are deformed and fitted at a predetermined interval, and when the rotational difference between the steering shaft 5 and the shaft 8 reaches a predetermined value, the shaft 8 and the steering shaft 5 come into contact with each other to directly transmit torque. . The shaft 8 is fastened to the universal joint 9 by serration engagement. An intermediate shaft (not shown) is connected to the universal joint 9, and this intermediate shaft is connected to a steering gear box. An upper end of the steering shaft 5 penetrates the lower jacket 2, and a steering wheel (not shown) is axially mounted on the upper end.

A known sensor mechanism is formed in the housing 3. That is, a bottomed cylindrical sensor built-in shaft 10 is fitted and fixed to the shaft 8, and the sensor built-in shaft 10 is
It is rotatably supported on. Shaft with built-in sensor 1
A coil spring 12 presses against the inner bottom portion of the shaft 8, and a ring 13 having an L-shaped cross section is in contact with the coil spring 12.
In the vicinity, it is fitted to the steering column 5 via the collar 14 so as to be movable in the axial direction.

A sliding collar 15 fitted to the steering shaft 5 movably in the axial direction is engaged with the collar 14, and a potentiometer 16 is provided in a circumferential groove provided in the sliding collar 15.
Are engaged with each other. Holes 17 are formed on the peripheral surface of the collar 14 so as to face each other in the diametric direction, and a ball 18 having substantially the same diameter is inserted into the hole 17. On the other hand, the steering shaft 5 facing the sliding collar 15 is formed with a groove 5b having a semicircular cross section in which the ball 18 rolls is formed in a substantially spiral shape so as to face each other in the diametrical direction.

The controller 19 includes, as shown in FIG.
On the upper side of the steering column, the steering column 1 is connected via a bracket 40 fixed to the housing 3.
And are arranged in parallel. The controller 19 can be stored in the lower part of the instrument panel 41.

Next, an iron ring 20 is press-fitted and fitted to the sensor built-in shaft 10.
A driven gear 21 made of a spur gear or helical gear having a special theoretical tooth profile made of resin is integrally formed on the outer peripheral portion of the driven gear 21. An output gear (motor pinion gear) 22 formed of a spur gear or helical gear having a special theoretical tooth profile meshing with the driven gear 21 is rotatably supported by the housing 3, and the output gear 22 projects from the electric motor 23. ing. The electric motor 23 is arranged on the housing 3 in parallel with the steering column.

The sensor built-in shaft 10 and the output gear 22
The guide plate 24 is rotatably fitted to the sensor built-in shaft 10 in order to keep the accuracy of the distance between the axial centers high, and the guide plate 24 is prevented from coming off by the C ring 25. An end of the output gear 22 is rotatably fitted to a peripheral portion of the guide plate 24. Therefore, the output gear 2
The distance between the shaft centers of the shaft 2 and the sensor-incorporated shaft 10 is accurately kept constant and does not change, thereby improving the durability of the gear.

The iron ring 20 press-fitted into the sensor built-in shaft 10 is set so as to cause a slip when the torque acting on the gear exceeds a predetermined value. That is, although the slip does not occur with the normal driving torque of the electric motor 23, if the electric motor 23 is locked,
By operating the steering wheel with a force equal to or greater than a predetermined value, a slip is generated between the sensor built-in shaft 10 and the iron ring 20, and steering from the steering wheel is enabled.

Therefore, when the steering shaft 5 is rotated about the axis via the steering wheel for steering, the steering shaft 5 rotates while twisting the torsion bar 6, and the steering shaft 5 and the sensor built-in due to the torsion of the torsion bar 6 are twisted. Shaft 10
The collar 14 and the sliding collar 15 compress or expand the coil spring 12 and move in the axial direction of the steering shaft 5 through the substantially spiral groove 5b and the ball 18 due to the rotation difference of the sensor arm of the potentiometer 16. 16a detects the right rotation or left rotation of the steering shaft 5, and inputs this signal to the controller 19.
The controller 19 commands the electric motor 23 to drive forward or reverse. Therefore, the electric motor 23 is driven to rotate forward or reverse, and the output gear 22 rotates the driven gear 21 to rotate the sensor built-in shaft 10 in a direction in which the torsion bar 6 is twisted. Therefore, the force for rotating the steering wheel is reduced.

Next, another embodiment of the present invention will be described. As shown in FIG. 3, a cylindrical portion 31 of a housing 30 is fitted to and fixed to the lower end of the lower jacket 2. The electric motors 33, 33 are fixed to motor fixing portions 32, 32 formed opposite to each other in the diameter direction. The output gear 34 of the electric motor 33 is a spur gear having a special theoretical tooth profile, and protrudes into the housing 30 from a through hole formed in the motor fixing portion 32. The number of the electric motors 33 is two or more,
Are arranged at regular intervals in the circumferential direction. Also, the electric motor 33
Is controlled by the controller as in the previous example.

On the other hand, the lower end of the steering shaft 5 is connected to a shaft 8 via a torsion bar 6 as in the previous example, and a universal joint 9 is connected to the shaft 8.
Further, an iron ring 20 is press-fitted into the sensor built-in shaft 10 fixed to the shaft 8, and a driven gear 21 made of a resin-made spur gear having a special theoretical tooth shape is integrally formed with the iron ring 20. The plurality of output gears 34 mesh. As for the sensor built-in shaft 10, the parts forming the sensor are related as in the previous example.
Is input to the controller.

Further, in order to always keep the distance between the shaft centers of the steering shaft 5 and the output gear 34 constant and with high accuracy, the guide plate 35 is connected to the sensor built-in shaft 10.
The guide plate 35 is locked by the C-ring 25 so as to be rotatable. The guide plate 35 has a through hole into which the plurality of output gears 34 are rotatably fitted. Although not shown, an intermediate shaft is connected to a lower end of the steering shaft 5 via a universal joint, and a steering wheel is axially mounted on an upper end of the steering shaft 5, as in the previous example.

Therefore, for steering, when the steering wheel is rotated, the steering shaft 5 is rotated, and the torsion bar 6 is twisted. The controller 19 that detects this twist drives the electric motor 33, and the output gear 34 is driven gear. By rotating the sensor built-in shaft 10 by rotating the shaft 21, the universal joint 9 is rotated via the shaft 8, so that the force for rotating the steering wheel is reduced.

When a large rotating force of the steering shaft 5 is required, a plurality of electric motors 33, 3 are provided.
3 can be controlled by the controller 6 to drive any one of the electric motors 33 when a small rotational force is sufficient. Thus, the output torque of one electric motor 33 can be reduced, so that the size of the electric motor 33 can be reduced.

The gear having a special theoretical tooth profile will be described. This gear is a highly durable tooth gear born from a new tooth profile theory. As shown in FIG. 4, the output gear 22 has, for example, a total of six teeth. The driven gear 21 on the driven side which meshes with the driven gear 21 has a total of, for example, 50 teeth 21a. A tooth gear characterized in that it is a continuous and differentiable function in which the curvature of the tooth profile curve periodically increases and decreases in the tooth bamboo direction.
This is a known gear disclosed in Japanese Patent No.

Therefore, referring to the outline of the gear having the special theory tooth profile from Tsutomu Komori's paper (Machine Design Magazine published in 1990), as shown in FIG.
They are arranged so as to be point-symmetric with respect to the intersection with the pitch line PL. With point symmetry, the root of the tooth becomes concave and the end of the tooth becomes convex. This reference rack tooth profile is composed of an involute curve continuously divided into minute sections,
The details of the number-th (i-th) involute curve separated by mn indicated by a solid line are shown. Ogt for ms
Is an involute curve formed from a base circle having a radius Gt centered on a circle, and an interval between sn is an involute curve formed from a base circle having a radius G1 centered on Og't. Mn on the tooth profile
The center of curvature at the point is located on the pitch line. The length between mn is adjusted by the magnitude of the angle delta, which is a parameter of the pressure angle.

FIG. 6 is a diagram showing a process of connecting involute curves divided into minute sections. The broken curve portion is an involute curve connected to the aforementioned mn. The condition for connecting the broken curves before and after this to the point m or the point n is that the radius of curvature is equal at the point m or the point n and the center is on the pitch line. Also, the base circle radius Gt
Is a function of the pressure angle and changes from Gt to Gt + 2.
The center of curvature is also on the pitch line at point n 'in the figure, and this pattern is thereafter repeated to form a rack tooth profile.

FIG. 7 shows a reference rack tooth profile drawn according to the above-described principle. The oblique line indicates the radius of curvature of the junction of the involute curve divided into small sections. As can be seen from the figure, there are many centers of curvature of the tooth profile on the pitch line. When this rack tooth profile is replaced with a rack tool (hob tooth profile), a tooth gear cut by this rack tool has many centers of curvature of the tooth profile on a pitch circle. Therefore, when the pair of gears mesh with each other, the relative curvature is 0 at all connection points, and the concave surface and the convex surface are engaged.

Thus, according to the present invention, the electric motor and the steering column are arranged in parallel, and the gear of the reduction mechanism is formed by a spur gear or a helical gear having a special theoretical tooth profile, and the inside of the housing accommodating the reduction mechanism. Since the guide plate that rotatably fits the shafts of the output gear and the driven gear is provided, the outer diameter of the gear is reduced, so that the electric steering device can be made compact.

Further, since the accuracy of the distance between the shaft centers of the output gear and the driven gear is improved by using the guide plate, the durability of the gear is improved. And
Since a spur gear or a helical gear is used for the reduction mechanism, the torque transmission efficiency is increased, and the motor output torque can be reduced accordingly, so that the size and cost of the electric motor can be reduced.

The driven gear has a resin gear integrally formed on the outer periphery of the iron ring and press-fits the iron ring to the shaft. When the torque acting on the gear exceeds a predetermined value, the driven gear is connected to the shaft. Therefore, even if the electric motor is locked, the steering wheel can be operated to transmit the steering torque. Therefore, the conventionally used clutch can be eliminated, and the cost can be reduced.

Furthermore, by integrating the controller on the housing, it is not necessary to consider the position of the conventional controller, for example, the lower side of the glove box on the passenger seat, and the unit can be reduced in size.

[0030]

According to the present invention described above, there is provided an electric power steering apparatus which assists the rotation of a steering shaft via a speed reduction mechanism comprising a driven gear fixed to the shaft and an output gear of an electric motor. Since the speed reduction mechanism is formed by a pair of spur gears or helical gears set to a high reduction ratio, and the speed reduction mechanism is housed in the housing, the electric motor can be provided close to the housing, and the steering can be provided. It is possible to reduce the size of the steering column in which the electric motor and the speed reduction mechanism are arranged on the column.

Further, by using the spur gear having the special theoretical tooth profile, the torque transmission efficiency is increased, the motor output torque is reduced accordingly, and the motor can be made more compact. Therefore, in this reduction mechanism, a required reduction ratio can be established in one stage of the motor pinion gear and the gear meshing with the motor pinion gear, and the outer diameter of the gear is reduced, so that the electric steering device can be made compact. .

[Brief description of the drawings]

FIG. 1 is a cross-sectional plan view showing an embodiment of the present invention.

FIG. 2 is a sectional side view of FIG.

FIG. 3 is a cross-sectional plan view showing another embodiment of the present invention.

Fig. 4 Tooth profile diagram of special theoretical tooth gear

FIG. 5 is an explanatory diagram of the theory of a special theoretical tooth profile.

FIG. 6 is an explanatory diagram of the theory of a special theoretical tooth profile.

FIG. 7 is an explanatory diagram of the theory of a special theoretical tooth profile.

[Explanation of Signs] 1 ... Steering column 2 ... Lower jacket 3 ... Housing 5 ... Steering shaft 6 ... Torsion bar 8 ... Shaft 9 ... Universal joint 10 ... Shaft with built-in sensor 20 ... Iron ring

Claims (2)

[Claims] 1. An electric power steering device which assists a rotation of a steering shaft via a speed reduction mechanism including a driven gear fixed to the shaft and an output gear of an electric motor, wherein the speed reduction mechanism is set to a high reduction ratio. An electric power steering device comprising a pair of spur gears or helical gears, and a reduction mechanism housed in a housing. 2. The electric power steering device according to claim 1, wherein the gear tooth profile of the speed reduction mechanism is formed by a special theoretical tooth profile.