JP2002276681A - Power transmission structure and electric power steering device including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power transmission structure having superior quietness and strength in, for example, a column type electric power steering device. SOLUTION: A power transmission joint A is an Oldham's coupling interposed between a metal motor shaft 16 and a worm shaft 18 aligned coaxially and transmitting a torque, and formed of superior-strength synthetic resin, for example, glass fiber reinforced PA66. After projecting threads 41 and 42 as connecting parts of the respective shafts 16 and 18 are covered with heat-contractive tubes 47A and 48A composed of PET (polyethylene terephthalate resin), those are contracted by heating so as to form synthetic resin films on the projecting threads 41 and 42. The synthetic resin films can prevent the hammering.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power transmission structure for connecting a drive shaft and a driven shaft via a power transmission joint, and an electric power steering device including the same.

[0002]

2. Description of the Related Art In a steering apparatus for an automobile, a first steering shaft connected to a steered wheel is connected to the first steering shaft via a torsion bar, and is connected to a steering mechanism. And a continuous second steering shaft. In the steering device, a relative displacement amount of the first and second steering shafts in the rotation direction is detected by a torque sensor, and the rotation of the motor shaft of the electric motor is reduced based on the detection result of the torque sensor. An electric power steering system that transmits a signal to a second steering shaft via a mechanism to assist the operation of the steering mechanism in accordance with the rotation of the steered wheels with the rotation of the electric motor, thereby reducing the labor burden on the driver for steering. A pick-up device is provided. As this type of electric power steering apparatus, there is known an electric power steering apparatus in which a steering assist unit including an electric motor, a power transmission joint, a reduction mechanism, and the like is arranged on a steering column or a rack and pinion portion. The former is called a column assist type electric power steering device (C-EPS). As the latter, R-EPS (rack assist type electric power steering device) for transmitting the torque of the electric motor to a rack bar extending along the vehicle width direction, D-D-EPS (direct drive type electric power Steering apparatus) and P-EPS (pinion assist type electric power steering apparatus) that assists a pinion that drives a rack.

A column assist type electric power steering apparatus will be described as an example. Since the steering assist unit is disposed in the vehicle interior, it is preferable to minimize the operating noise of the steering assist unit. At the connection between the motor and the motor shaft of the electric motor, or at the connection between the power transmission joint and the gear shaft of the reduction mechanism, there is a problem that a tapping sound is likely to occur. On the other hand, an Oldham coupling may be used as the power transmission coupling. In the Oldham coupling, the corresponding shaft forms a sliding pair with respect to the power transmission surfaces of the respective connection grooves formed at both ends thereof. For this reason, a predetermined amount of gap is required between each connection groove and the corresponding shaft to allow relative slippage, and the gap tends to increase the tapping sound.

Therefore, attempts have been made to reduce noise by using a synthetic resin for the power transmission joint. by the way,
In recent years, electrification of the power steering device has been advanced for vehicles having a large transmission torque, and a power transmission joint having a high strength capable of withstanding a large transmission torque is required. Therefore, in order to achieve high strength, it has been attempted to reinforce the synthetic resin used for the power transmission joint with glass fiber. The noise caused by the noise increases, and sufficient quietness cannot be obtained. Conversely, if a soft synthetic resin is used to ensure quietness, the strength is insufficient.

[0005] Such a problem exists not only in a power transmission joint used in a column assist type electric power steering device of an automobile but also in a general drive system. The present invention has been made in view of the above problems, and has as its object to provide a power transmission structure that is excellent in silence and has high strength, and an electric power steering device using the same.

[0006]

In order to achieve the above object, the present invention provides a drive shaft, a driven shaft, and a synthetic resin interposed between the drive shaft and the driven shaft for transmitting torque. And at least one of the drive shaft and the driven shaft is provided with a synthetic resin film on a connecting portion to the power transmission joint. . As the synthetic resin used for the power transmission joint, for example, a resin that emphasizes strength, such as glass fiber reinforced PA66, is selected to secure a sufficient connection strength.
Typically, such strong resins are relatively hard. Therefore, there is a possibility that a tapping sound may be generated between the power transmission joint and the metal member constituting the drive shaft or the like to be connected. ,
It is possible to suppress occurrence of hitting sound. As a result, the conflicting issues of sufficient quietness and high strength can be solved at once.

In the above power transmission structure, it is preferable that the coating is formed by heat-shrinking a heat-shrinkable tube. That is, if the tube is not yet contracted, it can be easily covered on the connecting portion such as the drive shaft. After the tube is covered, the tube can be heated and contracted, and the connecting portion can be covered and securely connected. The material of the heat-shrinkable tube is P
ET (polyethylene terephthalate), PFA (tetrafluoroethylene perfluoroalkyl vinyl ether copolymer), and ETTF (ethylene tetrafluoroethylene) can be used.

In the above power transmission structure, it is preferable that the coating is formed of a thermoplastic resin applied. For example, using a fluid immersion coating method, a heated connection portion such as a drive shaft may be immersed in a thermoplastic resin fluidized tank, and the thermoplastic resin may be melted and applied on the connected portion, You may apply using a body coating method. Examples of the thermoplastic resin to be applied include P11 such as PA11 and PA12.
A (polyamide resin) and PE (polyethylene resin) such as LDPE (low-density polyethylene) and HDPE (high-density polyethylene) can be used.

In the above power transmission structure, the power transmission joint may be provided with a connection groove having a rectangular cross section for connecting a corresponding shaft at a pair of ends thereof to constitute an Oldham coupling. preferable. That is, in the Oldham coupling, since the shafts corresponding to the power transmission surfaces of the respective connection grooves form a slip pair, a relative slip between the respective connection grooves and the corresponding shafts is allowed. A predetermined amount of gap is required, and the operating noise tends to be loud due to this gap. This is because the operating noise can be sufficiently reduced by the synthetic resin coating.

The above-described power transmission structure is applied to an electric power steering apparatus for assisting steering by transmitting a driving force of an electric motor to a steering shaft via a speed reduction mechanism. You may make it connect with the gear shaft of a mechanism via a power transmission joint. In this case, it is preferable to apply the present invention to a column-assist type electric power steering device as an electric power steering device in that noise in the interior of the vehicle is reduced and the user is not uncomfortable.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic diagram showing a configuration of an electric power steering apparatus to which a power transmission structure according to an embodiment of the present invention is applied. Referring to FIG.
An electric power steering device 1 (hereinafter, also simply referred to as the steering device 1) includes a steering shaft (steering shaft) 3 connected to a steering wheel (steering wheel) 2, and a steering shaft 3
And a rack shaft 6 that forms a rack gear 5 that meshes with the pinion gear 4 and extends in the left-right direction of the vehicle.

Tie rods 7 are respectively connected to both ends of the rack shaft 6, and each tie rod 7 is connected to a corresponding wheel 8 via a corresponding knuckle arm.
When the steering wheel 2 is operated and the steering shaft 3 is rotated, the rotation is converted by the pinion gear 4 and the rack gear 5 into a linear motion of the rack shaft 6 along the left-right direction of the vehicle. Thereby, steering of the wheel 8 is achieved. Steering axis 3
Is divided into a tubular first steering shaft 9 connected to the steered wheels 2 and a second steering shaft 10 connected to the pinion 4. The first steering shaft 9 and the second steering shaft 10 are connected to a torsion bar 11.
Are connected to each other on the same axis.

The first steering shaft 9 via the torsion bar 11
And a torque sensor 12 for detecting a steering torque based on a relative rotational displacement of the second steering shaft 10. A torque detection result of the torque sensor 12 is provided to a control unit 13. The control unit 13 controls the voltage applied to the steering assist electric motor 15 via the driver 14 based on the torque detection result. The motor shaft 16 of the electric motor 15 (FIG. 2)
) Is transmitted to the second steering shaft 10 via the speed reduction mechanism 17 including the worm mechanism, and the steering is assisted.

Referring to FIG. 2, a speed reduction mechanism 17 has a power transmission joint A at an end 16a of motor shaft 16 of electric motor 15.
A worm 19 formed integrally with a worm shaft 18 as a gear shaft connected through the worm shaft 18 and a worm wheel 2 integrally rotatably engaged with the second steering shaft 10.
0. The worm shaft 18 is connected to the second steering shaft 10.
Are arranged so as to intersect with the axis of. Worm shaft 1
8 first and second ends 21 and 2 facing each other in the axial direction
2 are first and second bearings 23, 2 using ball bearings.
4 and rotatably supported by first and second bearing holes 26 and 27 of the gear housing 25.

The worm shaft 18 is provided on the first and second bearings 2.
The worm 19 is integrally formed in an intermediate portion between the worms 3 and 24. The first end 21 of the worm shaft 18 is connected to the end 16a of the motor shaft 16 via a power transmission joint A. A backlash adjusting mechanism 28 is provided in association with the second bearing 24. Backlash adjustment mechanism 2
8 applies the urging force of the urging member 29 to the second bearing 24 via the member 30, and applies the second end 22 of the worm shaft 18 to the worm wheel 20 via the second bearing 24. To eliminate backlash between the worm 19 and the worm wheel 20. Reference numeral 30 denotes a biasing force adjusting screw, and reference numeral 31 denotes a lock nut. 33 is the second bearing 2
4 is a concave portion formed in the second bearing hole 27 to allow the deviation of 4.

Reference numeral 34 denotes a screw for positioning the worm shaft 18 in the axial direction via the first bearing 23. 35 is screw 3
4 is a lock nut for stopping the lock. Next, referring to FIG. 3, the power transmission joint A is constituted by a power transmission member 36 formed by injection molding a high-molecular synthetic resin material.
The power transmission member 36 has a shaft shape, and a first connection groove 39 is formed on opposing first and second ends 37 and 38.
Second connection grooves 40 are respectively formed.

The first connecting groove 39 is fitted into a ridge 41 as a connecting portion formed at the end 16a of the motor shaft 16 as a driving shaft. On the other hand, the second connecting groove 40 is formed on the second end 2 of the worm shaft 18 as a driven shaft (gear shaft).
The projections 42 are fitted into the ridges 42 as the connecting portions formed at the first position. This power transmission coupling A constitutes an Oldham coupling,
The ridges 41 and 42 function as a so-called slider. As shown in FIG. 4, a coating 47, 48 made of a synthetic resin is formed on each of the ridges 41, 42. After covering 48A on the ridges 41 and 42, it is formed by shrinking by heating. In this case, if the circumferential lengths of the tubes 47A, 48A before contraction are formed slightly larger than those of the corresponding ridges 41, 42, the ridges 41, 4 are formed.
2 can be easily covered. And after putting on,
When the tubes 47A and 48A are heated and shrunk, the synthetic resin films 47 and 4 firmly connected to the ridges 41 and 42, respectively.
8 can be obtained.

The heat-shrinkable tubes 47A and 48A are made of PET (polyethylene terephthalate), P
FA (tetrafluoroethylene perfluoroalkyl vinyl ether copolymer) and ETTF (ethylene tetrafluoroethylene) can be used. Tube 4
7A and 48A may be used by cutting a long one to a predetermined length corresponding to the length of the ridge. The thickness of the coatings 47 and 48 is, for example, 100 to 200 μm for PET.
For example, it can be set to 150 μm in the range of m. In the case of a PET tube, a strong coating due to shrinkage is possible by treatment at 140 ° C. for 5 minutes.

Referring again to FIG. 3, the ridge 41 of the motor shaft 16 has a substantially rectangular cross section, and has a pair of parallel flat power transmission surfaces 43, 43 forming a two-plane width. I have. The first connecting groove 39 corresponding to the ridge 41 is formed of a hole having a substantially rectangular cross section.
3 and 43, respectively, and have a pair of flat power transmission surfaces 45, 45 parallel to each other. The pair of power transmission surfaces 45, 45 are parallel to the axis of the power transmission member 36 and respectively extend along a pair of long sides of a rectangle formed by a cross section of the connection groove 39. The length of the long side of the rectangle formed by the cross section of the connecting groove 39 is set slightly longer than the length of the long side of the rectangle formed by the cross section of the ridge 41, and the end 16a of the motor shaft 15 and the power transmission joint A Is adapted to be relatively displaceable along the long side.

Similarly, the ridge 4 of the driven-side worm shaft 18
2 also has a substantially rectangular cross-section, and has a pair of flat surfaces parallel to each other forming a two-sided width and having power transmission surfaces 44,44. The second connection groove 40 corresponding to the ridge 42 is formed of a hole having a substantially rectangular cross section, and a pair of flat surfaces 44, 44 of the ridge 42.
A pair of parallel power transmission surfaces 4 respectively engaging with
6,46. The pair of power transmission surfaces 46 are parallel to the axis of the power transmission member 36 and extend along a pair of long sides of a rectangle formed by a cross section of the connection groove 40. The length of the long side of the rectangle formed by the cross section of the connection groove 40 is set slightly longer than the length of the long side of the rectangle formed by the cross section of the ridge 42, and the first end 21 of the worm shaft 18 and the power The transmission joint A can be displaced relative to the second end 38 along the long side.

The direction X in which the long side of the rectangle formed by the cross section of the connecting groove 39 extends (that is, the direction along which the power transmitting surfaces 45, 45 extend) and the direction Y in which the long side of the rectangle formed by the cross section of the connecting groove 40 extends. In other words, the power transmission surfaces 46, 46 intersect with each other, for example, so as to be substantially orthogonal.
The bottoms of both connecting grooves 39 and 40 communicate with each other.
According to the present embodiment, as the synthetic resin used for the power transmission joint A, for example, PA66 reinforced with glass fiber
Sufficient connection strength can be ensured by selecting a material that emphasizes strength such as (polyamide 66). The generation of a tapping sound between the power transmission joint A and a metal shaft such as the motor shaft 16 and the worm shaft 18 connected thereto is effectively suppressed by the synthetic resin coatings 47 and 48. can do. Thereby, high connection strength can be obtained while maintaining quietness.

In particular, since the power transmission coupling A constitutes an Oldham coupling, a particularly remarkable effect can be exhibited. That is, in the Oldham coupling, each of the connection grooves 39, 4
0, corresponding to the power transmission surfaces 45, 46
8 form a sliding pair, each connecting groove 39, 40
A predetermined amount of gap is required between the shaft and the corresponding shafts 16 and 18 to allow relative sliding therebetween, and this gap tends to increase operating noise. This is because it can be reduced to

Further, since this embodiment is applied to a column assist type electric power steering apparatus, a more remarkable effect can be exhibited. This is because in the column assist type electric power steering apparatus, quietness is particularly required because the steering assist unit including the electric motor 15, the power transmission coupling A, and the reduction mechanism 17 is disposed in the interior of the vehicle. However, by preventing the above-mentioned hitting sound, it is possible to remarkably reduce the noise in the interior of the vehicle and to prevent the user from feeling uncomfortable.

In the above embodiment, the synthetic resin films 47 and 48 are formed using the heat-shrinkable tubes 47A and 48A. However, the present invention is not limited to this.
The coatings 47 and 48 may be formed by applying a thermoplastic resin to the coating 42. As the thermoplastic resin, PA1
1, a polyamide resin such as PA12, or a polyethylene resin such as LDPE (low-density polyethylene) and HDPE (high-density polyethylene) can be used.

For applying the thermoplastic resin, a fluid immersion coating method or a powder coating method can be used. For example, in the flow dip coating method, the heated motor shaft 16 and the worm shaft 18 are heated.
Are immersed in a thermoplastic resin fluidization tank to melt the thermoplastic resin and
42. In addition, various changes can be made within the scope of the present invention.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering apparatus including a power transmission structure according to an embodiment of the present invention.

FIG. 2 is a sectional view of an electric motor, a power transmission joint, and a speed reduction mechanism of the electric power steering apparatus of FIG.

FIG. 3 is an exploded perspective view of the power transmission structure.

FIG. 4 is an exploded side view of the power transmission structure.

[Explanation of symbols]

 Reference Signs List 1 electric power steering device 3 steering shaft 9 first steering shaft 10 second steering shaft 11 torsion bar 15 electric motor 16 motor shaft (drive shaft) 17 reduction mechanism 18 worm shaft (gear shaft) 19 worm 20 worm wheel A power Transmission joint 36 Power transmission member 39 First connection groove 40 Second connection groove 41, 42 Ridge 43, 44 Power transmission surface 45, 46 Power transmission surface 47, 48 Coating 47A, 48B Tube

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Takeshi Tsuda 3-5-8 Minamisenba, Chuo-ku, Osaka Koyo Seiko Co., Ltd. F-term (reference) 3D033 CA02 CA04 3J009 DA11 EA05 EA19 EA23 EB20 EC07 FA08

Claims (5)

[Claims] 1. A power transmission coupling comprising a drive shaft, a driven shaft, and a synthetic resin interposed between the drive shaft and the driven shaft for transmitting torque, wherein at least one of the drive shaft and the driven shaft is A power transmission structure characterized in that a synthetic resin film is formed on a connecting portion to the power transmission joint. 2. A power transmission structure according to claim 1, wherein said coating is formed by heat-shrinking a heat-shrinkable tube. 3. The power transmission structure according to claim 1, wherein said coating is formed of a coated thermoplastic resin. 4. The method according to claim 1, wherein
A power transmission structure, wherein the power transmission joint is provided with a connection groove having a rectangular cross section for connecting corresponding shafts at a pair of end portions thereof to constitute an Oldham coupling. 5. An electric power steering system for assisting steering by transmitting a driving force of an electric motor to a steering shaft via a speed reduction mechanism by using the power transmission structure according to claim 1. An electric power steering apparatus, wherein a motor shaft of the electric motor and a gear shaft of a speed reduction mechanism are connected via a power transmission joint.