JP2002154442A - Motor-driven power steering device and rack shaft manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a motor-driven power steering device of dual pinion type capable of adopting a motor having a smaller output power while an existing facility is left serving and a rack shaft manufacturing method suitable therefor. SOLUTION: The motor-driven power steering device is composed of a rack shaft 5 having straight teeth 5a and 5b coupled with steering mechanisms 3 and 4, a first pinion 6 meshing with the first straight teeth 5a on the rack shaft 5 and transmitting the steering force from a steering wheel 9, and a second pinion 10 meshing with the second straight teeth 5b and transmitting the power from a motor 12, wherein the second straight teeth 5b have a wider pitch in the central part 5c than in the end part 5d, and therefore, the rack shaft 5 can be driven with a minor input when the steering angle has become large, and it is possible to reduce the maximum output power of the motor 12.

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 apparatus, and more particularly, to a pinion that meshes with rack teeth of a rack shaft to transmit a steering force from a steering wheel and an auxiliary steering force from a motor. The present invention relates to a so-called dual pinion type electric power steering device having a pinion.

[0002]

2. Description of the Related Art In an electric power steering system, a single pinion type electric motor transmits a steering force from a steering wheel and an auxiliary steering force of an electric motor to a rack shaft for driving a steering mechanism via the same pinion. There are a power steering apparatus of a type and a dual pinion type electric power steering apparatus of a type transmitting a steering force from a steering wheel and an auxiliary steering force of an electric motor to the rack shaft via different pinions.
The latter electric power steering device is often used when the electric motor cannot be arranged near the steering shaft due to the layout of the vehicle.

[0003] By the way, linear teeth of a rack shaft having no steering assist mechanism are formed by VGR (Variable Gear).
Ratio (Ratio) to reduce the steering force when the steering angle is increased has been conventionally performed. VG
R means the gear ratio by changing the pressure angle and the torsion angle of the rack teeth according to the rotation angle of the pinion, and consequently changing the pitch circle diameter and the pitch of the rack teeth meshing with the pinion. Is made variable. On the other hand, in a hydraulic or ball-screw assist type power steering apparatus, for example, when the steering angle is increased, except for improving the steering, there is a margin in the output auxiliary steering force. Does not require the use of VGR. Therefore, in the conventional electric power steering apparatus, both the single pinion type and the dual pinion type are CGR (Constant).
ant Gear Ratio, that is, a gear ratio that is constant regardless of the rotation angle of the pinion is used.

[0004]

On the other hand, in the dual pinion type as described above, since the output from the motor and the output from the steering wheel can be transmitted to the rack shaft in different systems, various types of VGR and CGR are used. Combinations are possible. As an example, in the case of an electric power steering device using an electric motor, the electric motor generally does not output much near the neutral position of the steering system, and often generates the maximum output near the maximum steering angle. The specifications of the electric motor are determined so that a necessary output can be obtained near the maximum steering angle. Therefore, in a dual pinion type electric power steering device, if VGR is used for the rack teeth meshing with the pinion connected to the motor, a smaller and lower output electric motor can be adopted, thereby reducing cost and cost. In addition, the weight and size of the device can be reduced.

[0005] In addition, there are cases where it is necessary to increase the rack thrust and improve the steering wheel turning followability due to the demand for larger vehicle models and vehicle dynamics to which the electric power steering device is applied. It would be preferable in terms of cost to be able to cope with these without increasing.

However, when forming the VGR type rack teeth on the rack shaft, hot working such as quenching is required. However, unlike the dual-pinion type rack shaft, hot working is required.
When the rack teeth are formed in one region, the rack shaft is relatively long, so that it is necessary to individually perform hot working. Here, of the two rack teeth, the rack teeth on the output side of the electric motor are set at a constant pitch, and the rack teeth on the output side of the steering wheel are set at a variable pitch. There is a problem in that thermal distortion occurs, which causes positional deviation and phase deviation in rack teeth having a constant pitch.

On the other hand, the problem of thermal distortion can be solved by hot working the entire rack shaft, but for this purpose, a new hot working of the entire rack shaft can be performed at once. There is a problem that a large facility must be provided, and the manufacturing cost is greatly increased.

The present invention has been made in view of the above problems, and provides an electric power steering apparatus capable of employing a motor having a lower output using existing equipment, and a method of manufacturing a rack shaft suitable for the electric power steering apparatus. The purpose is to do.

[0009]

In order to achieve the above object, a first aspect of the present invention is an electric power steering apparatus.
A rack shaft having straight teeth connected to a steering mechanism, and a first pinion meshing with a first region of the straight teeth of the rack shaft to transmit a steering force from a steering wheel;
A second pinion that meshes with a second region of the straight teeth of the rack shaft and transmits power from a motor, wherein one of the first region and the second region is a straight line. The pitch of the teeth is different between the region center and the region end, and in the other of the first region and the second region, the pitch of the straight teeth is equal at the region center and the region end. It is characterized by being.

[0010] In the rack shaft manufacturing method according to the second aspect of the present invention, the pitch of the straight teeth formed in the first region is different between the center of the region and the end of the region, and the pitch is formed in the second region. In the method of manufacturing a rack shaft in which the pitch of the linear teeth is equal at the center of the region and at the end of the region, the linear teeth of the first region are subjected to hot working, whereby the second region is formed. To reduce the possible phase error for the straight teeth of
The straight teeth in the second area are machined based on the straight teeth in the first area.

[0011]

According to the electric power steering apparatus of the present invention, a rack shaft having straight teeth connected to a steering mechanism;
A first pinion that meshes with a first region of the straight teeth of the rack shaft and transmits a steering force from a steering wheel; And a second pinion for transmitting power.
In one of the first region and the second region, the pitch of the straight teeth is different between a region central portion and a region end portion, and the other of the first region and the second region is Since the pitch of the straight teeth is equal at the center of the region and at the end of the region, for example, when the pitch of the end of the region is smaller than the pitch of the center of the region in the second region,
Since the rack shaft can be driven with a small output when the steering angle becomes large, the maximum output of the motor can be reduced.

According to the rack shaft manufacturing method of the present invention, the pitch of the straight teeth formed in the first area is different between the center of the area and the end of the area, and the pitch of the straight teeth formed in the second area is different. In the method of manufacturing a rack shaft in which the pitch of the teeth is equal at the center of the region and at the end of the region, hot working is performed on the straight teeth of the first region, thereby forming the second region. To reduce possible phase errors for straight teeth,
Since the straight teeth in the second area are machined based on the straight teeth in the first area, for example, using the conventional equipment that can only perform hot working locally on the rack shaft, 1
When hot working is performed on the straight teeth in the area of
By processing the straight teeth in the region of the first region based on the straight teeth in the first region, it is possible to suppress a position shift, a phase shift, and the like that may occur with respect to the straight teeth in the second region. You can get the axis.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic configuration diagram showing a dual pinion type electric power steering device of a vehicle according to an embodiment of the present invention.

In FIG. 1, tie rods 3a, 4a of steering mechanisms 3, 4 for steering wheels 1, 2 are connected to both ends of a rack shaft 5. The rack shaft 5 is supported by a gear box (not shown) so as to be movable in the longitudinal direction, and first rack teeth 5a are formed linearly in a left region in FIG. 1 and in a right region in FIG. The second rack teeth 5b are formed linearly.

A first pinion 6 meshes with the first rack teeth 5a. The first pinion 6 is connected to a steering shaft 8 via a torque sensor 7,
A steering wheel 9 is attached to an upper end of the steering shaft 8. The torque sensor 7 is electrically connected to the control device 13, detects the steering force transmitted to the steering shaft, and can transmit a detection signal corresponding to the steering force to the control device 13.
The control device 13 can also receive a signal corresponding to the vehicle speed from a sensor (not shown).

A second pinion 10 meshes with the second rack teeth 5b. The second pinion 10 includes the speed reducer 1
1 is connected to the electric motor 12. The electric motor 12 is electrically connected to the control device 13 and can output a steering assist force in accordance with a drive signal from the control device 13.

FIG. 2 is a front view of the rack shaft 5 according to the first embodiment. First rack teeth 5a of rack shaft 5
Has a regular pitch (CGR type),
The pitch of the second rack teeth 5b is large in the central region 5c, and the pitch is narrower toward the end regions 5d on both sides (VGR type). Therefore, the second pinion 10 meshing with the second rack tooth 5b also changes the pressure angle and the torsion angle of the rack tooth as the rotation angle increases with respect to the neutral position, resulting in a pitch circle diameter. In the end region 5d so as to be able to mesh with the rack teeth 5b, thereby achieving a variable gear ratio.

Next, the operation of the embodiment according to the present invention will be described below. The vehicle is in a straight-ahead state, and via a steering wheel 9 and a steering shaft 8,
If no steering force is input to the rack shaft 5, the torque sensor 7 does not generate an output signal as the input torque, and thus the electric motor 12 does not generate an auxiliary steering force.

When the driver turns the steering wheel 9 when the vehicle tries to turn a curve, the steering force is transmitted from the steering shaft 8 and the first pinion 6 to the rack shaft 5. The steering force at that time is detected by the torque sensor 7, and a detection signal is transmitted to the control device 13. The control device 13 determines an optimal auxiliary steering force based on the detection signal and the vehicle speed, and drives the electric motor 12 so as to output the auxiliary steering force. The auxiliary steering force output from the electric motor 12 is transmitted to the rack shaft 5 via the speed reducer 11 and the second pinion 10, whereby the steering of the driver is assisted.

Here, the second rack teeth 5b and the second pinion 10 have a configuration for realizing a variable gear ratio, and the gear ratio becomes larger as the rotation angle of the pinion 10 increases. In the vicinity of the maximum steering angle requiring a large auxiliary steering force, the electric motor 1
Even if the output of No. 2 is small, a large thrust can be generated by such a gear ratio, thereby increasing the rack thrust and improving the steering wheel turning followability without increasing the size of the system. Furthermore, the electric motor 12 having a small rating can be employed, and thus the manufacturing cost can be reduced.

Further, a method of manufacturing the rack shaft will be described. First, hot working is performed on the rack shaft 5 to form second rack teeth 5b of the VGR type. Here, when the second rack teeth 5b are hot-worked, the first rack teeth 5a may be displaced in the axial direction or shifted in phase due to the influence of thermal strain or the like. Therefore, the second rack teeth 5
After the hot working of b, CGR type cutting is performed on the first rack teeth 5a with reference to the second rack teeth 5b so that a positional shift and a phase shift in the axial direction are suppressed.
As a result, the rack shaft 5 with high accuracy can be formed without introducing new large-scale equipment.

FIG. 3 is a front view of a rack shaft according to a second embodiment, which can be used in the electric power steering apparatus of FIG. In the rack shaft 15, the first rack teeth 15 meshing with the first pinion 6 (FIG. 1)
In the case of V, the pitch is large in the central region 15c, and the pitch becomes smaller toward the end regions 15d on both sides.
GR type, while the second pinion 10 (FIG. 1)
The second rack teeth 15b meshing with are of the CGR type having an equal pitch.

Here, the first rack teeth 15a and the first pinion 6 have a configuration for realizing a variable gear ratio. In addition, the gear ratio increases as the rotation angle of the pinion 6 increases. Since the torque is set, the torque from the steering wheel 9 (FIG. 1) can be converted into a larger torque near the maximum steering angle that requires a large auxiliary steering force, so that even if the output of the electric motor 12 is small. ,
Appropriate steering can be achieved. As a result, it is possible to increase the rack thrust and improve the steering wheel turning followability without increasing the size of the system. Furthermore, the electric motor 12 having a small rating can be employed, and thus the manufacturing cost can be reduced.

According to the rack shaft 15 of the above-described embodiment, when the rotation angle of the steering wheel 9 is large, the driver's power required for steering is small, but when the steering angle is near the maximum steering angle. Since the rotation angle of the steering wheel with respect to the steering angle of the wheels 1 and 2 (FIG. 1) becomes large, when it is necessary to steer the wheels to the maximum steering angle such as when the vehicle is put in a garage, the driver rotates the steering wheel 9 greatly. There is a problem that must be done. An embodiment for solving such a problem will be described.

FIG. 4 is a front view of a rack shaft according to a third embodiment, which can be used in the electric power steering apparatus of FIG. In the rack shaft 25, the first rack teeth 25 meshing with the first pinion 6 (FIG. 1)
a is a modified VGR type in which the pitch is small in the central region 25c and the pitch is increased toward the end regions 25d on both sides, while the second meshing with the second pinion 10 (FIG. 1). The rack teeth 25b are of the CGR type having an even pitch.

Here, the first rack teeth 25a and the first pinion 6 have a configuration for realizing a variable gear ratio, and the gear ratio becomes smaller as the rotation angle of the pinion 6 increases. Since it is set, near the maximum steering angle, a smaller rotation angle from the steering wheel 9 (FIG. 1) can be converted into a larger axial movement of the rack shaft 25 as compared with the above-described embodiment, Even in such a case, the maximum steering angle of the wheels 1 and 2 can be obtained without rotating the steering wheel 9 greatly,
Thereby, the handling property is improved. Note that, in the present embodiment, it is preferable that the output of the electric motor 12 is large.

FIG. 5 is a front view of a rack shaft according to a fourth embodiment which can be used in the electric power steering apparatus of FIG. In the rack shaft 35, the first rack teeth 3 meshing with the first pinion 6b (FIG. 1)
5a is a CGR type having a regular pitch,
On the other hand, the second rack teeth 35b meshing with the second pinion 10 (FIG. 1) are of a modified VGR type in which the pitch is small in the central region 35c, and the pitch is increased toward the end regions 35d on both sides. is there.

As described above, the present invention has been described in detail with reference to the embodiments. However, the present invention should not be construed as being limited to the above-described embodiments, and may be appropriately modified and modified without departing from the spirit of the present invention. Of course, it can be improved.

[0029]

According to the electric power steering apparatus of the present invention, the rack shaft having straight teeth connected to the steering mechanism meshes with the first region of the straight teeth of the rack shaft.
A first pinion transmitting a steering force from a steering wheel, and a second pinion meshing with a second area of the straight teeth of the rack shaft and transmitting power from a motor, In one of the first region and the second region, the pitch of the straight teeth is different between the center of the region and the end of the region, and the other of the first region and the second region is the same as the straight tooth. Is equal at the center of the region and at the end of the region, for example, when the pitch of the end of the region is smaller than the pitch of the center of the region in the second region, the steering angle increases. When this happens, the rack shaft can be driven with a small output, thereby reducing the maximum output of the motor.

According to the method of manufacturing the rack shaft of the present invention, the pitch of the straight teeth formed in the first area is different between the center of the area and the end of the area, and the pitch of the straight teeth formed in the second area is different. In the method of manufacturing a rack shaft in which the pitch of the teeth is equal at the center of the region and at the end of the region, hot working is performed on the straight teeth of the first region, thereby forming the second region. To reduce possible phase errors for straight teeth,
Since the straight teeth in the second area are machined based on the straight teeth in the first area, for example, using the conventional equipment that can only perform hot working locally on the rack shaft, 1
When hot working is performed on the straight teeth in the area of
By processing the straight teeth in the region of the first region based on the straight teeth in the first region, it is possible to suppress a position shift, a phase shift, and the like that may occur with respect to the straight teeth in the second region. You can get the axis.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a dual pinion type electric power steering device of a vehicle, which is an embodiment of the present invention.

FIG. 2 is a front view of a rack shaft according to the first embodiment.

FIG. 3 is a front view of a rack shaft according to a second embodiment.

FIG. 4 is a front view of a rack shaft according to a third embodiment.

FIG. 5 is a front view of a rack shaft according to a fourth embodiment.

[Explanation of symbols]

 1, 2 wheels 3, 4 Steering mechanism 5, 15, 25, 35 Rack shafts 5a, 15a, 25a, 35a First rack teeth 5b, 15b, 25b, 35b Second rack teeth 6 First pinion 7 Torque sensor Reference Signs List 8 steering shaft 9 steering wheel 10 second pinion 11 speed reducer 12 electric motor 13 controller

Claims (2)

[Claims] A rack shaft having linear teeth connected to a steering mechanism; a first pinion meshing with a first region of the linear teeth of the rack shaft to transmit a steering force from a steering wheel; A second pinion that meshes with a second region of the straight teeth of the rack shaft and transmits power from a motor, wherein one of the first region and the second region is the straight line. The pitch of the teeth is different between the region center and the region end, and in the other of the first region and the second region, the pitch of the straight teeth is equal at the region center and the region end. An electric power steering device, comprising: 2. The pitch of the straight teeth formed in the first area is different between the center of the area and the end of the area, and the pitch of the straight teeth formed in the second area is different between the center of the area and the end of the area. In the method of manufacturing a rack shaft which is equal to a portion, by performing hot working on the linear teeth in the first area, it is possible to reduce a phase error that may occur in the linear teeth in the second area. A method of manufacturing a rack shaft, wherein the linear teeth in the second area are machined with reference to the linear teeth in the first area.