JP2907785B2 - Electric power steering device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an improvement of an electric power steering device mounted on a vehicle.

[0002]

2. Description of the Related Art In recent years, electric power steering devices have been frequently used in order to reduce the steering force of a steering wheel to provide a comfortable steering feeling. This type of electric power steering apparatus generates an auxiliary torque according to a steering torque by an electric motor and transmits the auxiliary torque to a steering system. For example, Japanese Patent Application Laid-Open No. Hei 7-165089 discloses a "steering apparatus". is there. According to FIGS. 1 and 3 of the publication, the ball nut mechanism 33 is used.
(The numbers are quoted from those described in the official gazette. The same applies hereinafter.) Is attached to one end of the rack shaft 2 and the rack shaft 2
A rack 8 is provided at the other end of the
Is engaged. Then, the rack shaft 2 is placed at the position where the pinion 6 and the rack 8 are engaged with each other.
A rack guide 10 is provided for pressing the engaging portion to eliminate play at the engaging portion. The rack guide 10 is pushed via the spring 12 by adjusting the screwing of the cap 11. As a result, the rack guide 10 presses the rack shaft 2 against the pinion 6.

FIGS. 9 (a) to 9 (c) are schematic illustrations of a conventional electric power steering apparatus. FIGS. 1 and 3 shown in the above prior art are described again to explain the prior art. FIG. Note that the reference numerals are different from those in the related art. 1A is a schematic plan view of a steering device. A steering device 100 has tie rods 102 and 102 and a knuckle arm 10 at both ends of a rack shaft 101. FIG.
The wheels 104, 104 are connected via the wheels 3, 103, and a ball nut mechanism 105 is connected to one end of the rack shaft 101.
And a rack 106 is provided at the other end of the rack shaft 101, and a pinion 107 is engaged with the rack 106,
The rack shaft 101 is pressed by a rack guide 108 from the opposite side of the pinion 107.

FIG. 1B shows a rack shaft 101 shown in FIG.
According to this schematic diagram, the rack shaft 101 is supported at two positions, that is, the position of the ball nut mechanism 105, the position of the pinion 107 and the position of the rack guide 108, and the support span is long. .

(C) shows the rack shaft 101 shown in (b) above.
FIG. 4 is a schematic operation diagram of the surroundings. According to this operation diagram, the road surface reaction force during traveling, particularly during steering, is reduced by the tie rods 102, 102.
Through the rack shaft 101. Therefore, external forces or moments (hereinafter, referred to as “moments M, M”) caused by the road surface reaction force act on both ends of the rack shaft 101. As a result, the rack shaft 101 bends in the vehicle longitudinal direction (vertical direction in the drawing) as shown by the solid line and the dotted line in this figure.

[0006]

By the way, in the steering apparatus shown in FIG. 9, the following points are mentioned as general causes of vibration of the rack shaft 101. (1) The road surface reaction force during traveling, particularly during steering, is
The vibration is transmitted to the rack shaft 101 through the second shaft 102 and the second shaft 102, and causes vibration of the rack shaft 101 in the longitudinal direction of the vehicle body (first trigger). (2) At the moment when each ball of the ball nut mechanism 105 comes into contact with and separates from the threaded portion of the rack shaft 101, the force acting on the threaded portion from the ball fluctuates. This is a trigger for generating vibration in the rack shaft 101 (second trigger).

When the frequency of the vibration caused by the first trigger matches the frequency of the vibration caused by the second trigger, the vibration of the rack shaft 101 shown in FIG. 9 is amplified. Moreover, when the frequency (frequency) of the amplified vibration matches the natural frequency of the rack shaft 101, the rack shaft 101 vibrates greatly due to resonance. When the rack shaft 101 vibrates greatly, the vibration is transmitted to the vehicle interior via the steering handle, and causes noise in the vehicle interior. Further, if vibration is transmitted to the steering handle, it is not preferable in terms of steering feeling. To suppress the resonance of the rack shaft 101, it is conceivable to change the natural frequency by changing the diameter of the rack shaft 101, or to provide a vibration damping member or the like on the rack shaft 101, but the rack shaft 101 becomes heavy. , The structure becomes complicated.

On the other hand, according to the technique disclosed in Japanese Patent Application Laid-Open No. Hei 7-165089, the rack shaft 2 is pressed against the pinion 6 via the spring 12 and the rack guide 10 by screwing and adjusting the cap 11. That is, the rack guide 10 preloads the rack shaft 2. Rack shaft 2
When vibrates in the front-rear direction of the vehicle body, the spring 12 expands and contracts accordingly, so that the rack guide 10 follows the vibration of the rack shaft 2. Therefore, even when the rack shaft 2 vibrates in the vehicle longitudinal direction, the rack guide 10 can apply a preload to the rack shaft 2 and can serve as a support point for the vibration of the rack shaft 2 in the longitudinal direction. .

From the viewpoint of preventing resonance, it is preferable that the natural frequency of the rack shaft 2 is large. And rack shaft 2
Even when the natural frequency of the rack guide 1 is large,
It is desirable that 0 always follow the vibration of the rack shaft 2 in the vehicle longitudinal direction. To do so, rack guide 1
It is necessary to increase the natural frequency of 0, and the natural frequency increases as the spring constant of the spring 12 increases. To increase the spring constant of the spring 12 composed of a coil spring, the coil center diameter D must be reduced, and the wire diameter d
And reducing the effective number of turns n. However, in consideration of the allowable stress of the spring 12, D / d cannot be made extremely small and the effective number of turns n cannot be made extremely small. The natural frequency of the rack guide 10 cannot be increased so much only by devising the spring 12.

Accordingly, an object of the present invention is to provide (1) a technique capable of easily suppressing vibration of a rack shaft during traveling, particularly during steering, with a simple structure, and (2) providing a rack guide with a simple structure. It is an object of the present invention to provide a technique capable of increasing a natural frequency and following a vibration of a rack shaft in a longitudinal direction of a vehicle body to a high frequency region.

[0011]

In order to achieve the above object, according to the present invention, a rack tooth is formed on one side of one end of a rack shaft extending in the vehicle width direction, and the rack tooth is formed on the rack tooth. Attach the pinion, attach a rack guide that pushes the back of the surface of the rack shaft on which the rack teeth are formed, form a thread at the other end of the rack shaft, attach a nut to this thread, and adjust the steering torque. In an electric power steering apparatus in which an auxiliary torque is applied to a rack shaft via a nut, a rack guide is arranged closer to the center of the vehicle than a pinion, and the rack shaft, the pinion, the rack guide, and the nut are collectively stored in a steering gear box. The adjustment screw member of the rack guide is screwed into the steering gear box, and the rear surface of the rack shaft is pushed only by the pressing force of the adjustment screw member. Characterized in that was.

External forces or moments (hereinafter, referred to as "moments") caused by the road surface reaction force act on both ends of the rack shaft. When the other end of the rack shaft is bent away from the pinion by the moment and the screw mechanism (combination of the screw portion and the nut), the rack shaft is supported only by the screw mechanism and the rack guide. On the other hand, when the other end of the rack shaft is bent in a direction in which the rack shaft is pressed against the pinion, the rack shaft has a structure in which bending can be suppressed by a screw mechanism, a rack guide, and a pinion. Therefore, the mode (mode) of bending or bending differs depending on the bending direction of the rack shaft. That is, when the rack shaft is deformed in the front-rear direction of the vehicle body by the road surface reaction force and the screw mechanism, the swing waveform when deforming forward and the swing waveform when deforming rearward have asymmetric shapes. Since the swing waveform is asymmetric,
The natural frequency of the rack shaft differs depending on the bending direction, and there is no fear of vibration amplification due to resonance. As a result, vibration of the rack shaft can be easily suppressed. When the vibration of the rack shaft is suppressed, the vibration of the steering handle is also suppressed, so that the steering feeling is enhanced. Further, since vibration transmitted to the vehicle interior via the steering handle is suppressed, noise in the vehicle interior can be prevented.

The rack guide applies a preload by pressing the back surface of the rack shaft on which the rack teeth are formed only by the pressing force of the adjusting screw member, so that the rack guide is affected by the vibration of the rack shaft in the longitudinal direction of the vehicle body. In other words, the rack shaft plays the role of a spring that affects the rack guide,
The natural frequency of the rack guide greatly depends on the spring constant of the rack shaft. The rack shaft has high bending stiffness, and as a result, the spring constant of the rack shaft is considerably larger than the spring constant of a conventionally used coil spring. Since the spring constant is large, the natural frequency of the rack guide is larger than that in the case where a conventional coil spring is used. For this reason, the rack guide can follow the vibration of the rack shaft in the front-rear direction of the vehicle up to the high-frequency region, and can sufficiently serve as a fulcrum. Therefore, the vibration of the rack shaft in the high frequency region can be easily suppressed, so that the steering feeling can be enhanced and the noise in the vehicle compartment can be prevented.

Further, since the conventional coil spring is not provided on the rack guide, the vibration of the rack shaft can be suppressed with a simple structure having a small number of parts, and the assemblability can be improved.
Productivity can be increased. Further, the rack guide can follow the vibration of the rack shaft in the longitudinal direction of the vehicle body to a high frequency range, so that the followability is improved. For this reason, the rack shaft does not cause the fluttering phenomenon caused by the vibration. Therefore, the wear of the rack and pinion mechanism and the screw mechanism can be reduced, and as a result, the life of the electric power steering device can be increased. Furthermore, since the rack guide was brought closer to the position of the screw mechanism,
The rack guide can apply a preload to the screw mechanism.
For this reason, rattling between the screw mechanism and the rack shaft can be suppressed, and as a result, the life of the screw mechanism can be increased.

[0015]

Embodiments of the present invention will be described below with reference to the accompanying drawings. The drawings should be viewed in the direction of reference numerals. FIG. 1 is a system diagram of an electric power steering device according to the present invention. The electric power steering device 1 includes a rack and pinion mechanism 3 (including a pinion 4 and a rack shaft 5) connected to a steering handle 2, and steering. A steering torque detecting means 6 for detecting a steering torque of the steering system generated by the steering wheel 2, a control means 7 for generating a control signal based on a detection signal of the steering torque detecting means 6, and a control signal of the control means 7 An electric motor 8 that generates an auxiliary torque corresponding to the steering torque based on the steering torque, and a ball screw (ball nut mechanism) 9 that transmits the auxiliary torque of the electric motor 8 to the rack shaft 5. And wheels (steering wheels) 13 via knuckle arms 12
13 is a device that steers 13.

FIG. 2 is an overall configuration diagram of the electric power steering apparatus according to the present invention, which is a view as seen from the rear of the vehicle body, and is a sectional view of a main part. The electric power steering device 1 includes a rack and pinion mechanism 3, an electric motor 8,
The ball screw 9 is collectively housed in a steering gear box 21 extending in the vehicle width direction (the left-right direction in this figure), and the steering gear box 21 is a substantially tubular first housing 22 bolted to each other in the longitudinal direction.
And the second housing 23. First housing 2
Reference numeral 2 denotes a bracket 24 for mounting to a vehicle body (not shown), and the second housing 23 includes a mounting member 25 for mounting to the vehicle body.

The rack shaft 5 extending in the vehicle width direction has a pinion 4 engaged with one end, a ball screw 9 is attached to the other end, and tie rods 11 are connected to both ends. It penetrates the steering gear box 21 so as to slide in the direction. The steering gear box 21 has a rack guide 50 mounted between the pinion 4 and the ball screw 9. That is, the rack guide 50 is arranged closer to the vehicle body than the pinion 4.
The rack and pinion mechanism 3 will be described in detail with reference to FIG. In the figure, 26, 26 are ball joints, 27, 2
7 is a rubber cover.

In the vehicle width direction, the axial center position of the ball screw 9 in the axial direction is A (hereinafter referred to as "ball screw center A"), and the center position of the engagement between the pinion 4 and the rack shaft 5 is B (hereinafter referred to as B). When the center position of the rack guide 50 is C (hereinafter, referred to as “rack guide center C”), the distance L ₁ from the ball screw center A to the rack guide center C is referred to as “L”. , the ratio between the distance L ₂ from the rack guide center C to the pinion center B, generally 3: 1 to 5: is preferably set to 1.

FIG. 3 is a sectional view taken along the line 3-3 in FIG. 2. The electric power steering apparatus 1 comprises a tubular input shaft 31 connected to the steering handle 2 (see FIG. 1), and an inner portion of the input shaft 31. Insert the upper part of the pin 32 into the input shaft 31
A main steering system is constituted by a torsion bar (elastic member) 33 connected by the above and an output shaft 34 which is serrated and connected to a lower portion of the torsion bar 33 and has the pinion 4 provided below.

The steering torque detecting means 6 is provided between the input and output shafts 3.
The steering torque of the steering system is detected by detecting the relative torsion angles 1 and 34, and comprises a torsion bar 33, a slider 35 and a sensor 36. More specifically, the torsion bar 33 is a member that literally generates a twist angle with respect to the torque, and the input shaft 3
1 and the output shaft 34 generate a relative torsional displacement.
A cylindrical slider 35 having an inclined groove 35a and a vertically long straight groove 35b is connected to the input shaft 31 and the output shaft 34.
And the slider 35 can be displaced in the axial direction according to the relative torsional displacement. The displacement at this time is proportional to the torque, and the displacement is converted into an electric signal by the variable inductance sensor 36.

The input shaft 31, the torsion bar 33 and the output shaft 34 are concentric. In the figure, reference numerals 41 and 42 denote a third housing and a fourth housing, which are mounted on an upper portion of the first housing 22. 43 is the input shaft 3
1 and bearings 44 and 45 for supporting both ends of the output shaft 34.

FIG. 4 is a sectional view taken along line 4-4 of FIG. The rack guide 50 is
An adjusting bolt 52 as an adjusting screw member is screwed into the first housing 22 of the steering gear box 21, and the rear surface (the left surface in the figure) of the rack shaft 5 is pushed only by the pressing force of the adjusting bolt 52. Specifically, the rack guide 50 includes a guide portion 51 that pushes out the rear surface of the rack shaft 4 and an adjustment bolt 52 that presses the guide portion 51.
And a lock nut 53 for locking the position of the adjustment bolt 52. The adjustment bolt 52 is provided in the first housing 2.
2 screw. The rack guide 50 having such a configuration applies a preload to the rack shaft 5 by the guide portion 51 by pressing the guide portion 51 with an appropriate pressing force by the adjustment bolt 53 screwed into the first housing 22, and 5 can be pressed against the pinion 4. In the figure, reference numeral 54 denotes a contact member provided on the guide portion.

FIG. 5 is a cross-sectional view taken along line 5-5 of FIG. 2 and shows a front surface as one side surface of one end of the rack shaft 5 (upper surface of FIG. 2).
The rack teeth 5a are formed on, engaging the pinion 4 with the rack teeth 5a, the rack guide center C away from the pinion center B by a distance L _2, the rear surface of the rack shaft 4 at the rack guide 50, i.e., the rack teeth This shows that the rear surface (the lower surface in this figure) of the surface on which 5a is formed is extruded. That is, the pinion 4 supports the rack shaft 5 from the front of the vehicle body, and the rack guide 50 presses the rack shaft 5 from the rear of the vehicle body.

FIG. 6 is a sectional view of a main part around a rack shaft, an electric motor and a ball screw according to the present invention. The electric motor 8 includes the stator 61 and the rotor 6 housed in the second housing 23.
The rotor 62 has a tubular output shaft 63 that is rotatably inserted through the rack shaft 5. The output shaft 63 has both ends rotatably supported in the first and second housings 22 and 23 via bearings 64 and 65, and has a nut 71 of the ball screw 9 in the other end.
Is attached. The bearing 65 supports the ball screw 9 via the output shaft 63 at or near the center A of the ball screw.

The ball screw 9 is connected to the nut 71 of the outer cylinder.
And a screw portion 5b formed on the rack shaft 5 operates via a ball (not shown), and the ball reaching the end of the screw groove of the nut 71 circulates through the tube, so-called internal portion. This is a general configuration of a circulation type or an external circulation type, and a detailed configuration is omitted for convenience. That is, the ball screw 9 is a screw mechanism including a combination of the screw portion 5b and the nut 71. In the figure, reference numeral 72 denotes a lock screw that is screwed into the inner surface of the output shaft 63, and prevents the nut 71 from moving in the axial direction with respect to the output shaft 63.

Next, the operation of the electric power steering apparatus having the above configuration will be described. FIGS. 7A to 7D are diagrams for explaining the operation of the electric power steering apparatus according to the present invention (first).
It is. FIG. 7A is a schematic plan view in which the electric power steering apparatus 1 of FIG. 2 is combined with the system of FIG. Note that the reference numerals of the respective parts are the same as those shown in FIGS. 1 and 2, and a description thereof will be omitted.

FIG. 7B is a further schematic diagram around the rack shaft 5 shown in FIG. 7A. The rack shaft 5 is supported by a ball screw center A and a pinion center B, and a rack guide center C is shown. Indicates that it was pressed. More specifically, since the ball screw 9 is assembled to the rack shaft 5, the ball screw 9 supports the rack shaft 5 from the front of the vehicle body and the rear of the vehicle body (vertical direction in the drawing). The pinion 4 supports the rack shaft 5 from the front of the vehicle body, and the rack guide 50 presses the rack shaft 5 from the rear of the vehicle body.

FIG. 7C is a schematic operation diagram (first) around the rack shaft 5 shown in FIG. 7B, and FIG.
It is a schematic operation figure (2nd) around the rack axis | shaft 5 shown to (b). At both ends of the rack shaft 5, an external force or moment (hereinafter, “moment Mf from the front of the vehicle body”, “moment Mr from the rear of the vehicle body”) due to the road surface reaction force and the ball screw 9 during traveling, particularly during steering, is described. ) Works. FIG.
(C), the moment Mf from the front of the vehicle body,
When the end of the rack shaft 5 is bent away from the pinion 4 by Mf, the rack shaft 5 is supported only by the ball screw 9 and the rack guide 50. As a result, the rack shaft 5 bends as indicated by the thick solid line in FIG.

On the other hand, as shown in FIG. 7D, when the end of the rack shaft 5 is bent in the direction of pressing against the pinion 4 by the moments Mr, Mr from the rear of the vehicle body, the rack shaft 5 The three members, the rack guide 50 and the pinion 4, have a structure in which bending can be suppressed. As a result, the rack shaft 5 bends with the ball screw center A, the pinion center B, and the rack guide center C as fulcrums, as indicated by the thick solid line in the figure.

Therefore, the mode (mode) of bending or bending differs depending on the bending direction of the rack shaft 5. That is, when the rack shaft 5 is deformed in the front-rear direction of the vehicle body due to the road surface reaction force and the ball screw 9, FIGS.
As described above, the oscillating waveform when deforming forward and the oscillating waveform when deforming backward have asymmetric shapes. Since the rocking waveform is asymmetric, the natural frequency of the rack shaft 5 differs depending on the bending direction, and there is no fear of vibration amplification due to resonance. As a result, vibration of the rack shaft 5 can be easily suppressed. When the vibration of the rack shaft 5 is suppressed, the vibration of the steering handle is also suppressed, so that the steering feeling is enhanced. Further, since vibration transmitted to the vehicle interior via the steering handle is suppressed, noise in the vehicle interior can be prevented. Since the rack guide center C is used as the fulcrum of the rack shaft 5, the distance between the fulcrums of the rack shaft 5 is short. As a result, the bending rigidity of the rack shaft 5 increases, and the natural frequency increases. Since the natural frequency is large, the region where no resonance occurs is wide.

As a result, the vibration of the rack shaft 5 can be easily suppressed. When the vibration of the rack shaft 5 is suppressed,
Since the vibration of the steering wheel is also suppressed, the steering feeling is enhanced. Further, since vibration transmitted to the vehicle interior via the steering handle is suppressed, noise in the vehicle interior can be prevented.

Further, the distance L ₁ from the ball screw center A to the rack guide center C, the ratio of the distance L ₂ from the rack guide center C to the pinion center B, approximately 3: 1
By setting 5: 1, the natural frequency of the rack shaft 5 and
The natural frequency of the mounting portion of the steering gear box 21 does not match. By shifting the resonance point of the rack shaft 5 from the resonance point of the portion where the steering gear box 21 for housing the steering system and the rack-and-pinion mechanism 3 is mounted, the vibration of the rack shaft 5 is not transmitted to the vehicle body. . Therefore, the noise in the cabin is further reduced, good commercial value is obtained, and the steering feeling is further enhanced.

FIGS. 8A and 8B are explanatory diagrams (second) of the operation of the electric power steering apparatus according to the present invention. FIG. 8A is a schematic plan view of the system shown in FIG. 1 combined with the electric power steering device 1 shown in FIG.
(B) is a schematic operation diagram. Actually, as shown in FIG. 8A, the adjusting bolt 52 of the rack guide 50 is
Preload is applied to the rack shaft 5. Therefore, FIG.
As shown in (b), the rack shaft 5 can be regarded as a both-end supporting beam supported at points A and B, and it can be regarded that a concentrated load acts on point C of this beam. The deflection δ of the rack shaft 5 at the point C is

[0034]

(Equation 1)

L ₁ : distance from ball screw center A to rack guide center C L ₂ : distance from rack guide center C to pinion center B P: pressing force (preload) of adjusting bolt 52 E: rack shaft 5; the second moment of area of the rack shaft 5; usually, the rack shaft 5 due to the pressing force P of the adjusting bolt 52;
Since the deflection δ is small, the pressing force P and the deflection δ have a linear relationship, so the above equation can be replaced with the following equation. δ = (1 / k) × P where k is

[0036]

(Equation 2)

K represents a pressing force required to deflect the rack shaft 5 by 1 mm, and can be called a "spring constant". By the way, the rack guide 50 has an adjustment bolt 52.
, The preload is applied by pressing the rear surface of the rack shaft 5 only by the pressing force of the rack shaft 5. That is, the rack shaft 5 is elastically deformable in the vehicle longitudinal direction as described above, and therefore can play a role of a spring for the adjustment bolt 52 of the rack guide 50. Therefore, to determine the natural frequency fn of the rack guide 50, the spring constant k of the rack shaft 5 may be considered. The natural frequency fn of the rack guide 50 is

[0038]

(Equation 3)

Where, m: mass of the adjusting bolt 52 The rack shaft 5 has high bending rigidity, and as a result, the rack shaft 5
Is significantly larger than the spring constant of a conventionally used coil spring. Since the spring constant k is large,
The natural frequency fn of the rack guide 50 is larger than that in the case where a conventional coil spring is used. For this reason, the rack guide 50 receives the vibration of the rack shaft 5 in the vehicle longitudinal direction.
It can follow up to a high-frequency region, and can sufficiently serve as a fulcrum.

In the above embodiment of the present invention,
The one end and the other end of the rack shaft 5 are not limited to only the ends of the rack shaft 5 but simply refer to positions for engaging the pinion 4 or assembling the ball screw 9 for convenience. is there. Further, the rack shaft 5 may be one in which rack teeth 5 a are formed on one side surface (for example, front surface), and the rear surface (for example, rear surface) of the surface on which the rack teeth 5 a are formed is extruded by the rack guide 50. Further, the rack guide 50
, An adjusting screw member is screwed into the steering gear box 21, a preload is applied to the rack shaft 5 only by an appropriate pressing force of the adjusting screw member, and the rack shaft 5 is connected to the pinion 4.
For example, an adjusting bolt 52 as an adjusting screw member may be configured to press the guide portion 51 and the contact member 5.
The configuration may also serve as the role of the fourth.

[0041]

According to the present invention, the following effects are exhibited by the above configuration. According to the first aspect of the present invention, a rack tooth is formed on one side surface of one end of a rack shaft extending in the vehicle width direction, and a pinion is engaged with the rack tooth, and the rear surface of the rack shaft on which the rack tooth is formed is formed. An electric power with a rack guide to be extruded, a screw formed on the other end of the rack shaft, a nut mounted on this screw, and an auxiliary torque corresponding to the steering torque applied to the rack shaft via the nut. In the steering device, the rack guide is arranged closer to the center of the vehicle body than the pinion, the rack shaft, the pinion, the rack guide, and the nut are collectively housed in the steering gear box. The rear surface of the rack shaft is pushed only by the pressing force of the screw member.

External forces or moments (hereinafter, referred to as "moments") caused by the road surface reaction force act on both ends of the rack shaft. When the other end of the rack shaft is bent away from the pinion by the moment and the screw mechanism (combination of the screw portion and the nut), the rack shaft is supported only by the screw mechanism and the rack guide. On the other hand, when the other end of the rack shaft is bent in a direction in which the rack shaft is pressed against the pinion, the rack shaft has a structure in which bending can be suppressed by a screw mechanism, a rack guide, and a pinion. Therefore, the mode (mode) of bending or bending differs depending on the bending direction of the rack shaft. That is, when the rack shaft is deformed in the front-rear direction of the vehicle body by the road surface reaction force and the screw mechanism, the swing waveform when deforming forward and the swing waveform when deforming rearward have asymmetric shapes. Since the swing waveform is asymmetric,
The natural frequency of the rack shaft differs depending on the bending direction, and there is no fear of vibration amplification due to resonance. As a result, vibration of the rack shaft can be easily suppressed. When the vibration of the rack shaft is suppressed, the vibration of the steering handle is also suppressed, so that the steering feeling is enhanced. Further, since vibration transmitted to the vehicle interior via the steering handle is suppressed, noise in the vehicle interior can be prevented.

The rack guide presses against the back surface of the rack shaft on which the rack teeth are formed only by the pressing force of the adjusting screw member to apply a preload, so that the rack guide is affected by the vibration of the rack shaft in the longitudinal direction of the vehicle body. In other words, the rack shaft plays the role of a spring that affects the rack guide,
The natural frequency of the rack guide greatly depends on the spring constant of the rack shaft. The rack shaft has high bending stiffness, and as a result, the spring constant of the rack shaft is considerably larger than the spring constant of a conventionally used coil spring. Since the spring constant is large, the natural frequency of the rack guide is larger than that in the case where a conventional coil spring is used. For this reason, the rack guide can follow the vibration of the rack shaft in the front-rear direction of the vehicle up to the high-frequency region, and can sufficiently serve as a fulcrum. Therefore, the vibration of the rack shaft in the high frequency region can be easily suppressed, so that the steering feeling can be enhanced and the noise in the vehicle compartment can be prevented.

Further, since the conventional coil spring is not provided in the rack guide, the vibration of the rack shaft can be suppressed with a simple structure having a small number of parts, and the assemblability can be improved.
Productivity can be increased. Further, the rack guide can follow the vibration of the rack shaft in the longitudinal direction of the vehicle body to a high frequency range, so that the followability is improved. For this reason, the rack shaft does not cause the fluttering phenomenon caused by the vibration. Therefore, the wear of the rack and pinion mechanism and the screw mechanism can be reduced, and as a result, the life of the electric power steering device can be increased. Furthermore, since the rack guide was brought closer to the position of the screw mechanism,
The rack guide can apply a preload to the screw mechanism.
For this reason, rattling between the screw mechanism and the rack shaft can be suppressed, and as a result, the life of the screw mechanism can be increased.

[Brief description of the drawings]

FIG. 1 is a system diagram of an electric power steering device according to the present invention.

FIG. 2 is an overall configuration diagram of an electric power steering device according to the present invention.

FIG. 3 is a sectional view taken along line 3-3 in FIG. 2;

FIG. 4 is a sectional view taken along line 4-4 in FIG. 2;

FIG. 5 is a sectional view taken along line 5-5 of FIG. 2;

FIG. 6 is a sectional view of a main part around a rack shaft, an electric motor, and a ball screw according to the present invention.

FIG. 7 is an operation explanatory view (first) of the electric power steering device according to the present invention;

FIG. 8 is a view for explaining the operation of the electric power steering apparatus according to the present invention (second).

FIG. 9 is a schematic explanatory view of a conventional electric power steering device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Electric power steering device, 2 ... Steering handle, 3 ... Rack and pinion mechanism, 4 ... Pinion, 5 ... Rack shaft, 5a ... Rack teeth, 5b ... Screw part, 8
... Electric motor, 9 ... Ball screw, 21 ... Steering gear box, 50 ... Rack guide, 51 ... Guide part, 52 ...
Adjustment bolt, 71 ... nut.

Claims (1)

(57) [Claims] A rack tooth is formed on one side surface of one end of a rack shaft extending in a vehicle width direction, a pinion is engaged with the rack tooth, and the rear surface of the rack shaft on which the rack tooth is formed is extruded. An electric power steering device in which a rack guide is mounted, a screw portion is formed at the other end of the rack shaft, a nut is mounted on the screw portion, and an auxiliary torque corresponding to the steering torque is applied to the rack shaft via the nut. In the above, the rack guide is disposed closer to the center of the vehicle than the pinion, the rack shaft, the pinion, the rack guide and the nut are collectively stored in a steering gear box, and the adjusting screw member of the rack guide is screwed into the steering gear box. An electric power steering device characterized in that the rear surface of the rack shaft is pushed only by the pressing force of the adjusting screw member. Place.