JPH09263250A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact electric power steering device using a special theoretical tooth form gear. SOLUTION: In an electric power steering device in which the rotation of a steering shaft 5 is assisted through a speed reduction mechanism which consists of the output gear 22 of an electric motor 23 fixed to the shaft 5, the electric motor 23 is arranged parallel to a steering column 1, and the gear of the above speed reduction mechanism is formed of a spur gear or a herical gear of a special theoretical tooth form, and a guide plate 24 to fit to the shafts of an output gear 22 and a driven gear 21 in a housing 3 to house the speed reduction mechanism, rotatable respectively, is provided to compose the electric power steering device.

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 which is made compact by using a special theoretical tooth gear for its reduction mechanism.

[0002]

2. Description of the Related Art A power steering device for a vehicle is a device for reducing steering wheel operating force to improve steering performance. Generally, hydraulic pressure is used, but in a light vehicle, an electric motor is used. The conventional electric power steering device is provided.

In the conventional electric power steering apparatus, the electric motor is rotated by rotating the steering shaft via a worm gear. This reduction mechanism
The torque transmission efficiency of the worm gear is low (60-80
%), If the reduction ratio remains unchanged, a larger motor output torque is required, resulting in an increase in the motor outer diameter. Therefore, a large number of machines have been provided in which a drive motor is mounted in parallel with a column and a spur gear is used as a speed reduction mechanism (Japanese Utility Model Laid-Open Nos. 62-144773 and 58-149255).
Reference).

[0004]

When a spur gear is used,
Since the torque transmission efficiency is high (about 95%), the motor output torque is correspondingly reduced, and the motor can be made compact. However, in this reduction mechanism, if the required reduction ratio is established in one stage of the motor pinion gear and the gear that meshes with the motor pinion, the minimum number of teeth of the pinion gear is limited to the involute tooth profile, so the outer diameter of the gear increases. However, there was a problem that it was still lacking in compactness. Further, if the one-stage structure is abandoned and the intermediate gear is interposed, there are new problems such as an increase in backlash and an increase in cost (see Japanese Utility Model Laid-Open No. 1-145668).

Therefore, the present invention is intended to solve the above-mentioned problems by applying a special theoretical tooth gear to an electric power steering apparatus.

[0006]

In order to solve the above-mentioned problems, according to the present invention, an electric motor is arranged in parallel with a steering column, and the gears of the speed reduction mechanism are formed by spur gears or helical gears having a special theoretical tooth profile. A spur gear or a helical gear different from the involute tooth profile, which is characterized in that guide plates for rotatably fitting the shafts of the output gear and the driven gear in the housing accommodating the reduction mechanism are provided. , A one-stage speed reduction mechanism is formed by using a special theoretical tooth gear. The special theoretical tooth gear can be formed with a minimum number of teeth of four, and the outer diameter of the gear can be reduced, so that the reduction gear mechanism can be downsized.

Then, the guide plate is fitted to the steering shaft for fixing the driven gear, and the output gear is rotatably fitted to the guide plate, so that the distance between the shaft centers of the output gear and the driven gear is highly accurate. It can be retained to prevent deterioration of durability.

Further, a plurality of output gears to be meshed with the driven gears, that is, a plurality of electric motors having the output gears are arranged, and the plurality of electric motors are selectively rotationally driven by the controller, so that a small torque is assisted. One of them can be driven when sufficient, and a plurality of them can be driven when a large torque is required to assist.

Further, the driven gear is formed by integrally forming a resin spur gear or a helical gear on the outer peripheral portion of an iron ring, press-fitting the iron ring onto the shaft, and when the torque acting on the gear exceeds a predetermined value, the iron ring is made of iron. It is characterized by slipping between the ring and the shaft, eliminating the risk of its locking due to the use of an electric motor, which would impede the rotation of the steering shaft.

Therefore, even when the electric motor is locked, if the force for rotating the steering wheel exceeds a predetermined value, the iron ring slips between itself and the steering shaft to rotate the steering wheel.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. As shown in FIGS. 1 and 2, the tubular portion 3a is fitted to the lower end portion of the lower jacket 2 of the steering column 1 to fix the housing 3, and the steering shaft 5 rotates through the bearing 4 in the tubular portion 3a. The steering shaft 5 is freely supported, and the lower end of the steering shaft 5 is supported by an end plate 3b with a bearing 4a interposed therebetween.
It is fitted to.

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 having a serration formed on the inner peripheral surface for engaging with the serration 6a is connected.

The end faces of the shaft 8 and the steering shaft 5 are irregularly fitted to each other with a predetermined gap, and when the rotational difference between the steering shaft 5 and the shaft 8 reaches a predetermined value, they 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 the intermediate shaft is connected to a steering gear box. An upper end portion of the steering shaft 5 penetrates the lower jacket 2 and a steering wheel (not shown) is pivotally attached to the upper end portion thereof.

A known sensor mechanism is formed in the housing 3. That is, the bottomed cylindrical sensor built-in shaft 10 is fitted and fixed to the shaft 8, and the sensor built-in shaft 10 is provided with the housing 3 via the bearing 11.
It is rotatably supported on. Shaft with built-in sensor 1
A coil spring 12 is pressed against the inner bottom of the shaft 0, and a ring 13 having an L-shaped cross section that abuts the coil spring 12 is attached to the shaft 8
The steering column 5 is fitted around the collar 14 via a collar 14 so as to be movable in the axial direction.

A sliding collar 15 fitted to the steering shaft 5 so as to be movable 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.
Sensor arm 16a is engaged. A hole 17 is formed in the circumferential surface of the collar 14 so as to face each other in the diametrical direction, and a ball 18 having substantially the same diameter is inserted into the hole 17. On the other hand, on the steering shaft 5 facing the sliding collar 15, grooves 5b having a semicircular cross section in which the balls 18 roll are formed in a spiral shape so as to face each other in the diametrical direction.

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

Then, an iron ring 20 is press-fitted and fitted into the sensor built-in shaft 10.
A driven gear 21, which is a spur gear or a helical gear having a special theoretical tooth profile made of resin, is integrally formed on the outer peripheral portion of the. An output gear (motor pinion gear) 22 composed of a special theoretical toothed spur gear or a helical gear that meshes 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 in the housing 3 in parallel with the steering column.

Shaft 10 with built-in sensor and output gear 22
In order to maintain the accuracy of the distance between the axes of the high accuracy, the guide plate 24 is rotatably fitted to the sensor built-in shaft 10, and the guide plate 24 is prevented from coming off by the C ring 25. The end of the output gear 22 is rotatably fitted to the peripheral edge of the guide plate 24. Therefore, the output gear 2
The distance between the centers of the shaft 2 and the shaft 10 with a built-in sensor is accurately maintained 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 that slip occurs when the torque acting on the gear exceeds a predetermined value. That is, the normal drive torque of the electric motor 23 does not cause a slip, but if the electric motor 23 is locked,
By operating the steering wheel with a force of a predetermined value or more, a slip occurs between the shaft 10 with a built-in sensor and the iron ring 20, and steering from the steering wheel is possible.

Therefore, when the steering shaft 5 is rotated about its 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 Shaft 10
Due to the difference in rotation of the coil spring 12, the collar 14 and the sliding collar 15 compress or extend the coil spring 12 via the substantially spiral groove 5b and the ball 18 to move in the axial direction of the steering shaft 5, thereby causing the sensor arm of the potentiometer 16 to move. 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 normally or reversely, and the output gear 22 rotates the driven gear 21 to rotate the shaft 10 with a built-in sensor in a direction in which the torsion of the torsion bar 6 is eliminated. 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, the tubular portion 31 of the housing 30 is fitted and fixed to the lower end portion of the lower jacket 2, and the tubular portion 31 is fixed to the housing 30. The electric motors 33, 33 are fixed to the motor fixing portions 32, 32 formed to face each other in the diametrical direction. The output gear 34 of the electric motor 33 is a spur gear having a special theoretical tooth shape, and projects 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, and the housing 30
They are arranged at regular intervals in the circumferential direction of. In addition, the electric motor 33
Is controlled by the controller as in the previous example.

On the other hand, a shaft 8 is connected to the lower end of the steering shaft 5 via a torsion bar 6 as in the previous example, and a universal joint 9 is connected to the shaft 8.
Further, the iron ring 20 is press-fitted into the sensor built-in shaft 10 fixed to the shaft 8, and the iron ring 20 is integrally formed with a driven gear 21 made of a resin-made special theoretical toothed spur gear. The plurality of output gears 34 mesh with each other. The sensor built-in shaft 10 is related to the parts forming the sensor as in the previous example.
Input the twist of 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 precision, the guide plate 35 is attached to the sensor built-in shaft 10.
Is rotatably fitted to the guide plate 35, and the C-ring 25 prevents the guide plate 35 from coming off. 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 the steering shaft 5 via a universal joint, and a steering wheel is pivotally attached to the upper end, which is the same as in the previous example.

Therefore, for steering, when the steering wheel is rotated, the steering shaft 5 rotates, the torsion bar 6 is twisted, and the controller 19 which detects the twist drives the electric motor 33, and the output gear 34 drives the driven gear. When the shaft 21 with a built-in sensor is rotated by rotating 21 to rotate the universal joint 9 via the shaft 8, the force for rotating the steering wheel is reduced.

When a large turning force of the steering shaft 5 is required, a plurality of electric motors 33, 3 are used.
The controller 6 can drive all of the motors 3 and drive any one of the electric motors 33 when a small rotational force is sufficient. As a result, the output torque of one electric motor 33 can be reduced, so that the electric motor 33 can be downsized.

A gear with a special theoretical tooth profile will be described. This gear is a highly durable tooth gear created from a new tooth profile theory. As shown in FIG. 4, the output gear 22 has a total of six tooth portions, for example. 22a, and the driven gear 21 on the driven side that meshes with the gear 22a has a total of, for example, 50 tooth portions 21a. A toothed gear characterized by being a continuous and differentiable function in which the curvature of a tooth profile curve periodically increases and decreases in the tooth take direction.
It is a known gear published in Japanese Patent Publication No.

Therefore, if the outline of the gear of the special theoretical tooth profile is quoted from the paper by Tsutomu Komori (machine design magazine published in 1990), the reference rack tooth profile is as shown in FIG.
It is arranged so as to be point-symmetric with respect to the intersection with the pitch line PL. By making point symmetry, the tooth root becomes concave and the tooth end becomes convex. This reference rack tooth profile is composed of involute curves that are continuously divided into minute sections,
The details of the several (i-th) involute curve in which mns shown by the solid line are separated are shown. Oms during ms
Is an involute curve formed from a basic circle having a radius Gt centered at, and sn is an involute curve formed from a basic circle having a radius G1 centered at Og't. Mn on 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 in which involute curves divided into minute sections are connected. The broken curve portion is an involute curve connected to mn described above. The condition that the broken curves before and after this are connected to the m point or the n point is that the radii of curvature are equal at the m point or the n point, and the center thereof is on the pitch line. Also, the basic circle radius Gt
The magnitude of is a function of 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 repeated thereafter to form a rack tooth profile.

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

[0030]

According to the present invention described above, the electric motor and the steering column are arranged in parallel, the gear of the reduction mechanism is formed by a spur gear or a helical gear having a special theoretical tooth profile, and the reduction mechanism is formed. Since the guide plates for rotatably fitting the shafts of the output gear and the driven gear in the housing to be housed are provided, the outer diameter of the gears becomes small, and therefore 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 as the reduction mechanism, the torque transmission efficiency is increased, and the motor output torque can be reduced accordingly, so that the electric motor can be downsized and the cost can be reduced.

In the driven gear, a resin gear is integrally formed on the outer peripheral portion of the iron ring, and the iron ring is press-fitted into the shaft. When the torque acting on the gear exceeds a predetermined value, the iron ring and the shaft are separated. Since the vehicle slips, the steering torque can be transmitted by operating the steering wheel even if the electric motor is locked. Therefore, the conventionally used clutch can be abolished, and the cost can be reduced.

Further, by integrating the controller on the housing, it is not necessary to consider the position of the conventional controller such as the lower side of the glove box in the passenger seat, and the unit can be downsized.

[Brief description of drawings]

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

FIG. 2 is a sectional side view of FIG.

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

[Fig. 4] Tooth profile of special theory tooth profile gear

[Figure 5] Illustration of the theory of special theory tooth profile

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

[Fig. 7] Illustration of the theory of special theory tooth profile

[Explanation of symbols]

 1 ... Steering column 2 ... Lower jacket 3 ... Housing 5 ... Steering shaft 6 ... Torsion bar 8 ... Shaft 9 ... Universal joint 10 ... Sensor built-in shaft 20 ... Iron ring 21 ... Driven gear 22, 34 ... Output gear 23, 33 ... Electric Motor 24, 35 ... Guide plate 25 ... C ring

Claims (4)

[Claims] 1. An electric power steering apparatus for assisting a rotation of a steering shaft through a reduction gear mechanism comprising a driven gear fixed to the shaft and an output gear of an electric motor, wherein the electric motor is arranged in parallel with a steering column. The gears of the mechanism are formed by special theoretical toothed spur gears or helical gears, and guide plates for rotatably fitting the output gear and driven gear shafts inside the housing that houses the reduction mechanism are provided. Characteristic electric power steering device. 2. A plurality of electric motors, the output gears of which are respectively meshed with driven gears, and the plurality of electric motors are selectively rotationally driven by a controller. Electric power steering device. 3. The controller is integrally attached to the housing of the speed reduction mechanism.
The electric power steering device described. 4. The driven gear is formed by integrally forming a resin gear on the outer peripheral portion of an iron ring and press-fitting the iron ring into the shaft. When the torque acting on the gear exceeds a predetermined value, the iron ring and the shaft are separated. The electric power steering device according to any one of claims 1 to 3, wherein the electric power steering device can slip between them.