JP2012096681A - Connecting structure of shaft and yoke of universal joint and electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a connecting structure of a yoke of a universal joint which is compact, lightweight and inexpensive and can bear a load of high torque.SOLUTION: An output shaft 16 fitted to a cylindrical part 47 of a first yoke 41 of a first universal joint 4 is fastened to the cylindrical part 47 by a fastening bolt 53. The output shaft 16 includes first and second male serrations 45 and 46 separated in a shaft direction of the output shaft 16 sandwiching the fastening bolt 53. The first male serration 45 is disposed on a tip side of the output shaft 16 of the fastening bolt 53. A module m1 of the first male serration 45 is larger than a module m2 of the second male serration by e.g. 0.2 to 0.3%.

Description

  The present invention relates to a coupling structure of a shaft and a universal joint yoke and an electric power steering apparatus using the same.

In general, in a vehicle steering apparatus, a rotational force from a steering wheel is transmitted to a steering mechanism such as a rack and pinion mechanism via a steering shaft (steering shaft), an intermediate shaft (intermediate shaft), etc. This steers the steered wheels.
The upper end of the intermediate shaft is connected to the steering shaft via a universal joint, and the lower end of the intermediate shaft is connected to the pinion shaft via a universal joint. As a structure for coupling a shaft such as a steering shaft, an intermediate shaft, and a pinion shaft to a yoke of a corresponding universal joint, there is a structure shown in FIG.

  In this structure, the shaft is inserted into the cylindrical portion of the universal joint yoke. Female serrations are formed on the inner peripheral surface of the cylindrical portion. The cylindrical portion is formed with an axial slit, and a pair of tabs are extended from a pair of edges of the slit. By tightening the pair of tabs with the fastening bolts penetrating the pair of tabs, the shaft serrated and fitted to the cylindrical portion is fastened and fixed.

JP 2000-234629 A

The shaft has a circumferential groove with which a fastening bolt is engaged. A front male serration and a rear male serration having the same shape are formed on both sides of the circumferential groove. The front male serration is disposed closer to the distal end side of the shaft than the circumferential groove.
Usually, the yoke of the universal joint has a tightening bolt insertion hole disposed at a position relatively close to the end portion on the side where the shaft is inserted. For this reason, the amount of deformation of the cylindrical portion when the tightening bolt is tightened tends to be small at the portion where the front male serration is tightened and large at the portion where the rear male serration is tightened.

Thus, the rear male serration tightly engages the corresponding female serration while the front male serration loosely engages the corresponding female serration. That is, the coupling strength between the shaft and the yoke is substantially ensured only by the meshing of the rear male serration. For this reason, there exists a problem that it cannot endure the load of high torque.
Although it is conceivable to increase the size of the serration, in such a case, the manufacturing cost may increase, the weight may increase, or the size may increase, making it difficult to lay out the vehicle. For this reason, in recent years, it has not been possible to cope with the increase in output of electric power steering devices that have been requested.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a coupling structure of a shaft and a universal joint yoke that can withstand a high torque load with a small size, light weight, and low cost. As a result, high output can be achieved with a small size, light weight, and low cost. An electric power steering apparatus is provided.

  In order to achieve the above object, according to the present invention, the shaft (16) fitted to the tubular portion (47) of the yoke (41) of the universal joint (4) is fastened to the tubular portion by the fastening shaft (53). In the coupling structure (P) of the shaft and the universal joint yoke, the shaft includes first and second male serrations (45, 46) spaced apart in the axial direction (X1) of the shaft across the clamping shaft. The first male serration is disposed closer to the distal end of the shaft than the fastening shaft, and the first male serration module (m1) is larger than the second male serration module (m2). A coupling structure of a shaft and a universal joint yoke is provided.

The cylindrical portion of the yoke of the universal joint has a portion corresponding to the first male serration and a portion corresponding to the second male serration located on the tip side of the fastening shaft, and the first male serration. There is a tendency that the deformation of the portion corresponding to is relatively small.
According to the present invention, the module of the first male serration is made larger than the module of the second male serration. Therefore, when the fastening shaft is tightened, the cylindrical portion of the yoke corresponding to the first male serration is Even if the deformation amount of the portion is relatively small, the meshing rate between the first male serration and the female serration of the portion of the cylindrical portion of the yoke corresponding thereto can be increased. Thereby, both the first and second male serrations can be tightly meshed with the corresponding female serrations. Therefore, the connection strength between the universal joint and the shaft can be increased, and a high torque load can be withstood. Compared to the conventional structure, it is only necessary to change the module of the first male serration, and it is possible to provide a structure that can withstand a high torque load in a small size, light weight, and low cost. Module changes can be easily performed, for example, when male serrations are rolled.

  In addition, the lower limit value (m1-e1) of the tolerance range of the first male serration module may be larger than the upper limit value (m2 + e2) of the tolerance range of the second male serration module ( Claim 2). In this case, the difference between the first and second male serration modules can be easily realized by shifting the tolerance range of the first and second male serration modules.

  The number of teeth (z1) of the first male serration may be equal to the number of teeth (z2) of the second male serration (claim 3). Since the module is a value obtained by dividing the pitch circle diameter by the number of teeth, making the module different corresponds to making the pitch circle diameter different between the first and second male serrations. That is, the pitch circle diameter of the first male serration is increased to improve the meshing rate of the first male serration.

Further, in the present invention, the coupling structure (P) of the shaft and the universal joint yoke is used as the structure for coupling the shaft (16) for transmitting the steering force of the steering member (2) to the universal joint yoke (41). An electric power steering device (1) is provided (claim 4). According to the present invention, high output can be achieved in a small size, light weight and low cost.
In the above description, the alphanumeric characters in parentheses represent reference numerals of corresponding components in the embodiments described later, but the scope of the claims is not limited by these reference numerals.

1 is a schematic diagram showing a schematic configuration of an electric power steering apparatus including a coupling structure of a shaft and a universal joint yoke according to a first embodiment of the present invention. It is a schematic side view of the said coupling structure. It is sectional drawing which follows the III-III line of FIG. It is sectional drawing which follows the IV-IV line of FIG. It is sectional drawing which follows the VV line of FIG.

A preferred embodiment of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic configuration diagram of an electric power steering apparatus 1 to which a coupling structure P of a shaft and a universal joint yoke according to an embodiment of the present invention is applied. Referring to FIG. 1, an electric power steering device 1 includes a steering shaft 3 connected to a steering member 2 such as a steering wheel, and an intermediate shaft 5 connected to the steering shaft 3 via a first universal joint 4. A rack shaft 8 as a steered shaft having a pinion shaft 7 connected to the intermediate shaft 5 via a second universal joint 6 and a rack 8a meshing with the pinion 7a provided in the vicinity of the end of the pinion shaft 7. It has.

  A steering mechanism A1 is configured by a rack and pinion mechanism including the pinion shaft 7 and the rack shaft 8. The rack shaft 8 is supported by a housing 10 fixed to the vehicle body side member 9 so as to be movable in an axial direction along the left-right direction of the vehicle (a direction orthogonal to the paper surface). Although not shown, each end of the rack shaft 8 is connected to a corresponding steered wheel via a corresponding tie rod and a corresponding knuckle arm.

  The steering shaft 3 includes a first steering shaft 11 and a second steering shaft 12 that are connected coaxially. The first steering shaft 11 has an upper shaft 13 and a lower shaft 14 which are fitted so as to be able to rotate together and be slidable relative to each other in the axial direction using spline coupling. One of the upper shaft 13 and the lower shaft 14 constitutes an inner shaft, and the other constitutes a cylindrical outer shaft.

The second steering shaft 12 includes an input shaft 15 connected to the lower shaft 14 so as to be able to rotate together, an output shaft 16 connected to the intermediate shaft 5 through the first universal joint 4, an input shaft 15 and And a torsion bar 17 for connecting the output shaft 16 so as to be relatively rotatable.
The steering shaft 3 is rotatably supported by a steering column 20 fixed to the vehicle body side members 18 and 19 via a bearing (not shown).

The steering column 20 includes a cylindrical upper jacket 21 and a cylindrical lower jacket 22 that are fitted so as to be relatively movable in the axial direction, and a housing 23 connected to the lower end in the axial direction of the lower jacket 22. The housing 23 houses a speed reduction mechanism 25 that decelerates the power of the steering assisting electric motor 24 and transmits it to the output shaft 16.
The speed reduction mechanism 25 has a drive gear 26 that is connected to a rotation shaft (not shown) of the electric motor 24 so as to be able to rotate together with the drive gear 26 and a driven gear 27 that meshes with the drive gear 26 and rotates together with the output shaft 16. . The drive gear 26 is composed of, for example, a worm shaft, and the driven gear 27 is composed of, for example, a worm wheel.

  The steering column 20 is fixed to the vehicle body side members 18 and 19 via an upper bracket 28 on the vehicle rear side and a lower bracket 29 on the vehicle front side. The upper bracket 28 can be fixed to the upper jacket 21 of the steering column 20 via a column bracket described later. The upper bracket 28 uses a fixing bolt (stud bolt) 30 that protrudes downward from the vehicle body side member 18, a nut 31 that is screwed to the fixing bolt 30, and a capsule 32 that is detachably held by the upper bracket 28. The vehicle body side member 18 is fixed.

The lower bracket 29 is fixed to the housing 23 of the steering column 20. Further, the lower bracket 29 is fixed to the vehicle body side member 19 using a fixing bolt (stud bolt) 33 protruding from the vehicle body side member 19 and a nut 34 screwed into the fixing bolt 33.
The intermediate shaft 5 includes a lower shaft 35 made of, for example, an inner shaft, and an upper shaft 36 made of, for example, an outer shaft and fitted to the lower shaft 35 so as to be slidable relative to the axial direction and to be able to rotate together. .

In the present embodiment, the coupling structure P between the shaft and the universal joint yoke is applied to a structure in which the output shaft 16 of the second steering shaft 12 and the yoke of the first universal joint 4 are coupled. As will be described, the present coupling structure P may be applied to a structure that connects the pinion shaft 7 and the yoke of the second universal joint 6.
As shown in FIG. 2, the first universal joint 4 includes a first yoke 41 to which an end portion 16 a of the output shaft 16 of the second steering shaft 12 is coupled, and an end portion of the upper shaft 36 of the intermediate shaft 5. A second yoke 42 connected and a cross shaft 43 connecting the first yoke 41 and the second yoke 42 are provided. A circumferential groove 44 is formed on the outer periphery of the end portion 16 a of the output shaft 16, and a first male serration 45 and a second male serration 46 are formed on both sides of the circumferential groove 44. .

Referring to FIG. 3, which is a cross-sectional view taken along line III-III in FIG. 2, the first yoke 41 has a cylindrical portion 47 to which the end portion 16 a of the output shaft 16 of the second steering shaft 12 is fitted. Have. The cylindrical portion 47 is provided with a slit 48 extending in the axial direction. The first yoke 41 has a pair of tabs 49 and 50 on both sides of the slit 48.
Fastening bolts 53 as fastening shafts are inserted into bolt insertion holes 51 and 52 provided in the respective tabs 49 and 50. The pair of tabs 49 and 50 are tightened between the nut 54 engaged with the tip of the tightening bolt 53 and the head 53 a of the tightening bolt 53, whereby the end portion 16 a of the output shaft 16 is connected to the cylindrical portion 47. It is tightened inside.

  A female serration 55 is formed on the inner periphery of the tubular portion 47. The female serration 55 meshes with the first male serration 45 as shown in FIG. 4, and as shown in FIG. Meshes with two male serrations 46. The cylindrical portion 47 has a portion 471 corresponding to the first male serration 45 and a portion 472 corresponding to the second male serration 46 on both sides of the clamping bolt 53.

The feature of the present embodiment is that the module m1 of the first male serration 45 is made larger than the module m2 of the second male serration 46. That is, the expression m1> m2 is satisfied.
Specifically, when the diameter of the output shaft 16 is about 15 to 25 mm, it may be exemplified that the first module m1 is set to 0.2 to 0.3% higher than the second module m2. it can. As a result, the pitch circle diameter of the first male serration 45 can be made approximately 30 to 45 μm larger than the pitch circle diameter of the second male serration 46, thereby substantially increasing the size of the first male serration 45. Can be planned.

  According to the present embodiment, the module m1 of the first male serration 45 on the front end side of the output shaft 16 (that is, inserted into the back side of the tubular portion 47) is made more than the module m2 of the second male serration 46. Since the tightening bolt 53 is tightened, even if the deformation amount of the portion 471 of the cylindrical portion 47 of the first yoke 41 corresponding to the first male serration 45 is relatively small, the first The meshing rate between the male serration 45 and the female serration 55 of the portion 471 of the cylindrical portion 47 of the first yoke 41 corresponding to the male serration 45 can be increased. Thereby, both the first male serration 45 and the second male serration 46 can be tightly engaged with the female serration 55 of the tubular portion 47.

  Therefore, it is possible to increase the connection strength between the first universal joint 4 and the output shaft 16 as a shaft, and to withstand a high torque load. Compared to the conventional structure, it is only necessary to change the module m1 of the first male serration 45, and it is possible to provide a coupling structure that can withstand a high torque load in a small size, light weight and low cost. As a result, high output of the electric power steering apparatus 1 can be achieved in a small size, light weight and low cost.

When the first and second male serrations 45 and 46 of the output shaft 16 are rolled, the male serrations 45 and 46 can be easily manufactured by changing the module according to the rolling site.
The present invention is not limited to the above-described embodiment. For example, the tolerance range of the module m1 of the first male serration 45 and the tolerance range of the module m2 of the second male serration 46 are shifted (shifted). Thus, the difference between the modules m1 and m2 of the first and second male serrations 45 and 46 may be easily realized.

  Specifically, when the tolerance of the module m1 of the first male serration 45 is ± e1 (e1 is a positive value), the lower limit value (m1-e1) of the tolerance range of the module m1 of the first male serration 45 Is larger than the upper limit value (m1 + e2) of the tolerance range of the module m2 of the second male serration 46 when the tolerance of the module m2 of the second male serration 46 is ± e2 (e2 is a positive value). . That is, the formula (m1-e1)> (m2 + e2) is satisfied.

  In the above embodiment, the coupling structure P of the present invention is applied to the coupling structure of the output shaft 16 of the second steering shaft 12 and the first yoke 41 of the first universal joint 4. Any one of the steering shaft 3, the intermediate shaft 5 and the pinion shaft 7 serving as a shaft for transmitting force can be applied to a structure in which the corresponding universal joints 4 and 6 are coupled to corresponding yokes. In addition, various modifications can be made within the scope of the claims of the present invention.

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering device, 2 ... Steering member, 3 ... Steering shaft, 4 ... First universal joint, 5 ... Intermediate shaft, 6 ... Second universal joint, 7 ... Pinion shaft, 8 ... Rack shaft, A1 ... Steering mechanism, P ... coupling structure (of shaft and universal joint yoke), 11 ... first steering shaft, 12 ... second steering shaft, 16 ... output shaft, 16a ... end, 24 ... electric motor, 25 ... deceleration Mechanism 41 ... first yoke 42 ... second yoke 43 ... cross shaft 45 ... first male serration 46 ... second male serration 47 ... cylindrical part 48 ... slit 49,50 ... Tab, 51, 52 ... Bolt insertion hole, 53 ... Fastening bolt (tightening shaft), 55 ... Female serration, X1 ... Axial direction

Claims (4)

In the coupling structure of the shaft and the universal joint yoke, which fastens the shaft fitted to the cylindrical part of the universal joint yoke to the cylindrical part by the fastening shaft,
The shaft includes first and second male serrations spaced apart in the axial direction of the shaft across the fastening shaft,
The first male serration is disposed closer to the distal end side of the shaft than the fastening shaft,
A coupling structure of a shaft and a universal joint yoke, wherein the module of the first male serration is made larger than the module of the second male serration.   2. The shaft and universal joint according to claim 1, wherein the lower limit value of the tolerance range of the first male serration module is larger than the upper limit value of the tolerance range of the second male serration module. Yoke coupling structure.   3. The coupling structure of a shaft and a universal joint yoke according to claim 1, wherein the number of teeth of the first male serration is equal to the number of teeth of the second male serration.   The electric power steering using the coupling structure of the shaft and the universal joint yoke according to any one of claims 1 to 3, as a structure for coupling the shaft for transmitting the steering force of the steering member to the universal joint yoke. apparatus.

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