Rotary shafts – gudgeons – housings – and flexible couplings for ro – Shafting – Nonmetalic shaft or component
Reexamination Certificate
2000-07-27
2002-06-25
Browne, Lynne H. (Department: 3629)
Rotary shafts, gudgeons, housings, and flexible couplings for ro
Shafting
Nonmetalic shaft or component
C464S183000, C464S902000, C138S114000, C138S143000
Reexamination Certificate
active
06409606
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the invention
The present invention relates to power transmission shafts. More particularly, it relates to those that can be used such as for propeller shafts and drive shafts, which constitute a power transmission system of vehicles.
2. Related Art
Shafts constituting the power transmission system of a vehicle include a propeller shaft for transmitting power from the gearbox to the reduction gear unit and a drive shaft for connecting the engine and the hub joint. The shafts, which are provided at the ends thereof with universal joints, are adapted to respond to a change in length and angle due to a variation in relative position between the gearbox and the reduction gear unit or between the engine and the hub joint.
FIG. 9
is an overall external view of a prior-art propeller shaft
1
. Metal joint elements or stub shafts
3
,
4
are connected to the both ends of an intermediate shaft
2
. The stub shafts
3
,
4
mate with the inner joint members of constant velocity joints
5
,
6
via splines or serrations.
FIGS. 10A and 10B
are views of an intermediate shaft of a drive shaft.
FIG. 10A
illustrates an intermediate shaft
7
with no dynamic damper, while
FIG. 10B
illustrates an intermediate shaft
8
with a dynamic damper
9
for preventing vibrations. In the prior art, hollow or solid steel shafts have been generally used for the intermediate shaft
2
of the propeller shaft
1
and the intermediate shafts
7
,
8
of the drive shaft.
At present, from the viewpoint of flexural rigidity, long power transmission shafts made of steel need to be divided and provided with a bearing for supporting the intermediate portion thereof or with a dynamic damper at the intermediate portion thereof. Thus, the shafts are currently in need of some improvements in weight, cost, and the like.
For example, such an example has been suggested as employs a pipe formed of a fiber reinforced plastic (hereinafter referred to as “FRP”) having a high specific strength. However, the joint portions thereof cannot be formed of FRP in one piece in terms of rigidity and strength and thus metal joints are connected to the end portions of the FRP. To connect the joints, the sleeve of the metal joint is press-fitted into or adhered to the end portions of the FRP pipe. On the other hand, Japanese Patent Laid-Open Publication No. Sho 55-118831 describes a method in which metal joints are inserted into an FRP pipe and thereafter the pipe is wound in conjunction with the joints by continuous fibers that are impregnated with resin. Alternatively, Japanese Patent Laid-Open Publication No. Sho 63-199914 suggests a method in which the fitted portions of the metal joints are formed in a non-circular shape and then the end portions of the shaft are heated to a temperature over the glass transition temperature thereof, and then the end portions are crimped onto the fitted portions of the joints. Other connecting methods were also employed in order to ensure the strength of joint portions and thus realize the transmission of torque. According to those methods, the cross section of the shaft end portions was formed in the shape of a polygon or the joint surfaces with which the shaft end portions of a hollow shaft overlap were formed to be coarse by knurling or the like. Alternatively, a hollow shaft made of FRP was crimped and metal parts were press-fitted into the center portion of the hollow shaft to be connected to joints. In addition, various methods were devised to maintain the strength of joint portions in the case of connection with adhesive interposed in between the contact surfaces of the end portions of a hollow shaft made of FRP and metal parts. Those methods include a combination of adhesive and making the surfaces coarse, crimping, or press-fitting.
However, these methods presented such problems that the shaft end portions were worked with difficulty or the outer diameter of the shaft had to be made larger to ensure the strength of the joints. Moreover, additional means had to be provided for preventing the joints from dropping off from the shaft in the axial direction in order to ensure reliability. In addition, the method for crimping a hollow shaft made of FRP had a serious disadvantage of lacking long-term reliability. The method may cause slipping to occur along the circumference or the shaft to slip off in the axial direction due to a decrease in binding force when the shaft is press-fitted, the decrease being caused by creep or a stress relaxation of the FRP portion. Furthermore, particularly in the case of drive shaft, many shafts could not provide torque transmission capacity enough to satisfy the product requirements due to an excessive torque. Furthermore, another problem was present in using a hollow shaft made of FRP as the intermediate shaft of a power transmission shaft to provide a reduction in weight, in fuel consumption, in cost, and in vibration and noise. That is, the shaft could not be made larger in diameter because enough space near the mounting portion of the shaft was not available within a vehicle.
SUMMARY OF THE INVENTION
In view of the foregoing problems, an object of the present invention is to provide a power transmission shaft with highly reliable joints, with high rigidity (a high natural bending frequency), light in weight, and low in cost in order to respond to the aforementioned demands for improvement.
The aforementioned problems by inserting an FRP pipe is inserted into a metal pipe in a power transmission shaft comprising metal joint elements and the metal pipe connected to each other. High rigidity can be provided for the shaft and the shaft can be made longer at the same time by interposing the hollow pipe made of FRP with high flexural rigidity inside the metal pipe. Moreover, providing improved rigidity for the shaft obviates the need for a support bearing or a dynamic damper at the intermediate portion, which were conventionally required for a long shaft, thus realizing a reduction in weight and cost. Furthermore, from a material viewpoint, it is a matter of course to be able to reduce the shaft in weight by concurrently using the metal pipe and the FRP pipe.
In addition, since the FRP pipe is inserted into the metal pipe to form a composite shaft, the metal portions form the joints on the end portions of the shaft. This allows the shaft to have strength sufficient to endure even large shearing and thus can transmit force with reliability. That is, reliable and perfect joint methods can be employed such as welding or friction welding of metal joint elements to a metal pipe. Consequently, no such deficiency occurs as sliding along the circumference of the pipe or slipping-off in the axial direction and thus the joint portions can be provided with long-term reliability.
Furthermore, FRP layers to be inserted into the metal pipe, having the fiber alignment angles of 0 and +/−45 degrees with respect to the axial direction of the metal pipe, can be stacked alternately. This is preferable in that flexural rigidity and torsional rigidity can be controlled. Alternatively, the flexural and torsional rigidity and buckling resistance may be controlled by the length of the FRP pipe to be inserted into the metal pipe, the wall thickness ratio between the metal pipe and the FRP pipe, the modulus of elasticity of the reinforcing fibers used, or the like.
It is preferable to employ a material with low density and large modulus of elasticity as the fibers constituting the FRP pipe in order to provide a high natural bending frequency for the composite shaft. Such fibers include PAN-based and pitch-based carbon fibers, silicon carbide fibers, alumina fibers, boron fibers, glass fibers, para-aramid fibers (for example, Kevler, trademark of Du Pont), and metal fibers (steel, aluminum alloy, titanium alloy, copper, and tungsten fibers).
The tensile modulus of reinforcing fibers used is preferably not less than 20000 kgf/mm
2
(196 GPa) and more desirably not less than 25000 kgf/mm
2
(245 GPa). If the tensile mudulus of the reinfo
Kodama Hitoshi
Nakajima Tatsuo
Takano Tsuneo
Arent Fox Kintner & Plotkin & Kahn, PLLC
Browne Lynne H.
NTN Corporation
Thompson Kenn
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