Bearing structure of a wiper arm

Abstract: In a wiper arm, the leading end of an arm support and the base end of an arm shank with a blade are rockably pivoted through a support shaft, and a bushing unit (6) composed of a bearing (6a) which the support shaft pierces and a resin material (6b) is pressed into a bearing hole bored at the leading end of the arm support. Since the peripheral surface of the bearing has concave portions and convex portions and the concave portions remain rough after the peripheral surface is processed, the adhesion between the bearing and the resin material is improved.

Description: Field of the Invention The present invention relates to a bearing structure of a wiper arm attached to an automobile or the like, Description of the Related Art In this kind of wiper arm, an arm shank with a blade at its leading end is pivotally connected at the leading end of an arm support whose base end is integrally fixed to a wiper shaft, and the arm shank and the arm support are urged by a spring beyond a supporting point so that the blade abuts against a glass plane with a proper wiping force. Conventionally, as shown in Fig.6, when an arm shank is pivotally connected at an arm support 2, a bushing unit 6 is provided, comprised of a bearing and a resin sleeve. The bearing may be formed by sintering and the sleeve may be insert-moulded around the bearing. The bushing unit 6 is pressed into a bearing portion of the arm support so as to prevent the arm support 2 and the bearing from being directly in contact with each other. The arm support 2 is coated beforehand, and the coating material intrudes into the bearing hole 2a, which makes it difficult to accurately control the inner diameter of the bearing hole 2a. The whole of the outer surface of the bearing is smoothed as a result of a sizing process when the bearing is manufactured. Because of this the adhesive force of the bearing to the resin material is low. When the bushing unit 6 is pressed into the bearing hole 2a of the arm support 2, the press-in load can be heavy because of the aforementioned problem with the dimensional tolerances of the bearing hole 2a. Thus, as the bushing unit is pushed in, high stresses can be generated in the leading edge of the bushing unit and the resin material sometimes separates from the bearing, and cracks (such as A in Figure 6) can be generated, both of which lower the reliability of the wiper arm. US-A-4,932,097 discloses a bonding unit wherein a resin sleeve insulates a sintered bearing from a wiper arm, although the sleeve is not adhered to the bearing (See e.g. column 3, lines 55 to 60 and Figure 8 of US-A-4,932,097 : "... and an intermediate member 34 ... covering the outer periphery of said oilless bearing 13"). GB-A-2,113,319 discloses a bearing for a motor which is fitted inside a thermoplastic frame, and held in place by interengaging grooves and protrusions in the resin and bearing contact surfaces. SUMMARY OF THE INVENTION It is an object of the present invention to provide a bearing structure of a wiper arm capable of overcoming the problems discussed above. In a wiper arm of the present invention of the type disclosed in US-A-4,932,097 and defined in claim 1, the leading end of an arm support fixed on the side of a wiper shaft and the base end of an arm shank with a blade are pivotally connected through a support shaft. The support shaft extends through a bushing unit comprised of a bearing and a sleeve of resin material. This bushing unit is put into place by pressing into a bearing hole bored at the leading end of the arm support. The peripheral surface of the bearing has concave portions and convex portions such that the concave portions of the peripheral surface remain rough even after the peripheral surface is processed. This sizing process may be required to reduce the bearing maximum outside diameter by removing a layer of said convex portions. The concave portions therefore remain rough and un-processed even after the periphery of the bearing surface is processed, which processing removes excess material from the raised convex portions alone. The peripheral surface thereby formed has both the original rough-like sections and smooth outside surface sections, strengthening the adhesive force between the resin material and the bearing relative to a conventional bearing. Therefore the formation of cracks in the resin material and separation of the resin from the bearing outer surface is prevented while the resin material is being pressed into the bearing hole. Further developments in line with claim 1 are referred to in the dependent claims 2 to 7. BRIEF DESCRIPTION OF THE DRAWINGS The drawings show an embodiment of a bearing structure of a wiper arm according to the present invention. Fig. 1 is a vertical cross-sectional view of an arm portion of a wiper arm; Fig. 2 is a plan view of the arm portion; Fig. 3 is a principal enlarged cross-sectional view showing the state in which a bushing unit has been pressed into a bearing hole; Fig. 4 is a principal enlarged cross-sectional view showing the state in which a support shaft is inserted to provide a pivot; Fig. 5 is an enlarged perspective view of the bearing which is a component of the bushing unit; and Fig. 6 is an explanatory view of a prior art bushing unit during pressing into the arm support. DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described with reference to the accompanying drawings. In Figure 1, a wiper shaft 1 is drivingly connected to a wiper motor (not shown), and the base end of an arm support 2 is mounted on the wiper shaft 1 by a nut 3. A blade 5 is attached to the leading end of an arm shank 4, and the base end of the arm shank 4 is pivotally connected to the leading end of the arm support 2. A bearing hole 2a in Figure 6 is bored at the leading end of the arm support 2, and a bushing unit 6, described below, is pressed into said hole. The approximately inverse-U-shaped base end of the arm shank 4 is placed on the leading end of the arm support 2 from above so that the arm support 2 and the arm shank 4 are pivotally connected by a support shaft 7. A spring 8 is disposed between the arm shank 4 and a point on the arm support 2 beyond the supporting point (the axial center of the support shaft 7). This spring 8 urges the blade 5 against a glass plane during wiping. The bushing unit 6 is comprised of a bearing 6a formed by a sintering process and a resin material 6b formed by insert molding around the bearing so as to cover the outer surface of the bearing 6a with a sleeve. The outer surface of the bearing 6a has concave portions and convex portions as shown in Figure 6. Sizing processing is carried out before insert moulding of the sleeve, and only affects the convex portions, leaving the concave portions in the rough, as-sintered state. In the above embodiment of the present invention, when the wiper arm is assembled, the bushing unit 6 is pressed into the bearing hole 2a of the arm support 2. Strong adhesion exists between the bearing 6a and the resin material 6b both because of the rough planes of the bearing surface and the increased adhered surface area. Thus, during assembly, even when the press-in load is increased as the bushing unit 6 is pressed into the bearing hole 2a, separation of the resin material 6b from the bearing 6a is substantially prevented, and cracking in the resin material is also substantially prevented, thereby greatly enhancing the subsequent reliability of the wiper arm in service.

Claims: A wiper arm comprising a wiper shaft (1), an arm support (2) fixed on the side of said wiper shaft (1), an arm shank (4), and a blade mounted to said arm shank (4), the leading end of said arm support (2) and the base end of said arm shank (4) being pivotally connected by a support shaft (7) in a bushing unit (6) comprising a bearing (6a) through which said support shaft (7) extends and a resin or resin-like sleeve (6b), which unit (6) is mounted within a bearing hole (2a) formed in the leading end of the arm support (2), characterised in that; a) the sleeve (6b) of resin or resin-like material is adhered to the outside of said bearing (6a); and b) the bearing (6a) is provided with an outside surface having convex and concave portions, thereby increasing the area of adhesion between the bearing (6a) and the sleeve (6b), and c) in that said portions have a rough-like surface, thereby promoting strong adhesion; whereby when the bearing unit (6) is mounted by pressing into a bearing hole (2a) formed in the leading end of said arm support (2), the enhanced adhesion between the bearing (6a) and the sleeve (6b) prevents failure of the sleeve. A wiper arm according to claim 1, wherein said bearing is formed by a sintering process and the rough-like surface is the as-sintered surface condition. A wiper arm according to claims 1 or 2, wherein said bearing (6a) is subjected to a sizing process which reduces the bearing maximum outside diameter by removing a layer of said convex portions. A wiper arm as claimed in claim 3 wherein the concave portions define rough planes on the bearing surface. A wiper arm as claimed in claims 3 and 4 wherein the convex portions are the smooth outside surface defined by the bearing maximum outside diameter. A wiper arm according to any preceding claim, wherein said concave and convex portions extend longitudinally of the bearing (6a). A wiper arm as previously claimed wherein the resin sleeve (6b) is formed around the bearing (6a) by insert moulding, thereby producing intimate adhesive contact between said resin sleeve (6b) and said bearing (6a).

Inventors: IKEZAWA RYU, KISHI HIRONOBU, IKEZAWA, RYU, KISHI, HIRONOBU
Applicants: MITSUBA ELECTRIC MFG CO, MITSUBA ELECTRIC MFG. CO., LTD.
Application year: 1991
Main classification: B60S1
IPC codes: B60S1