SLIDING BEARING

Abstract: A sliding bearing formed by providing annular grooves (2a) in an inner circumferential surface of a bearing alloy layer (2), and covering the bearing alloy layer (2) with an intermediate layer (3) and an overlaying layer (4) in the mentioned order, wherein, when the bearing is worn, the overlaying layer (4) and intermediate layer (3) which remain in the annular grooves (2a), and ridges (2b) between the annular grooves (2a) in the bearing alloy layer (2) are exposed. Let h equal the height of the ridges (2b), t the thickness of the intermediate layer (3), t a longitudinal axis and h a lateral axis in the present invention. The thickness t and height h are set in the ranges in which they satisfy the conditions of the following three expressions: 1≦h<5, t≦2h/3+1/3 , t≦3. More preferably, they are set in the ranges in which they satisfy the conditions of the following two expressions: 1≦h<5, t≦h/2 . The unit of the h and t is µm. This enables an initial abrasion resistance, and the post-abrasion seizure resistance and compatibility of the overlaying layer to be improved.

Description: Technical Field The invention relates to a sliding bearing, and more particularly, to a sliding bearing including a bearing alloy layer, an intermediate layer and an overlay layer. Background of the Invention A sliding bearing is known in the art comprising a bearing alloy layer having a multitude of circumferentially extending and axially spaced annular grooves formed around the inner peripheral surface thereof to define a circumferentially extending peak between a pair of axially adjacent annular grooves, an intermediate layer which coats the surface of the bearing alloy layer, and an overlay layer which coats the surface of the intermediate layer, the arrangement such that when the overlay layer and the intermediate layer are partly abraded beginning from the surface of the overlay layer, the overlay layer and the intermediate layer which remain in the recess of the annular groove as well as the peak of the bearing alloy layer are exposed (see Japanese Laid-Open Patent Application No. 205,014/1985 and corresponding European Application No. EP-A-155 257). With a sliding bearing thus constructed, when the overlay layer and the intermediate layer are partly abraded beginning from the surface of the overlay layer, the overlay layer and the intermediate layer which remain in the recess of the annular groove as well as the peak of the bearing alloy layer are exposed, thus preventing the intermediate layer from being extensively exposed immediately, as experienced in a sliding bearing of the the kind which is not provided with such annular grooves, which would cause a substantial reduction in the seizure resistance as a result of an extensive exposure of the intermediate layer. However, in the cited Japanese Laid-Open Patent Application, it is described that the intended effect is achieved only when the depth of the annular groove or the height of the peak is equal to or greater than one and one-half the thickness of the intermediate layer and be equal to or greater than 5 µm. Disclosure of the Invention However, as a result of various experiments conducted with varying thicknesses of the intermediate layer or varying heights of the peak, it is found that bearing performance which is excellent in respects of affinity and seizure resistance is obtained even with a peak height which is less than 5 µm. Accordingly, the invention basically provides a sliding bearing having a height of peak which is less than 5 µm and which exhibits an excellent bearing performance in respects of affinity and seizure resistance. Specifically, according to a basic aspect of the invention, the sliding bearing according to the preamble of claim 1 is characterized by the features according to the second portion of claim 1. According to another preferred embodiment of the invention, the thickness t satisfies additionally the following requirement: t ≤ h/2 According to this embodiment of the invention; an affinity and a seizure resistance which are superior to those exhibited by a conventional sliding bearing are achieved, as will be demonstrated by test results to be described later. When these additional requirements are not satisfied, the invention itself provides good affinity and seizure resistance which are stabilized, even though the superiority of performance is reduced as compared with that obtained with the second aspect. Brief Description of the Drawings Fig. 1 is a cross section of a sliding bearing according to the invention; Fig. 2 graphically shows the range in which the requirements of the invention are satisfied; and Fig. 3 is a chart of test results indicating the abrasion resistance at the beginning of use of the invention, the seizure resistance and the affinity after the overlay layer is abraded. Best Mode of Carrying Out the Invention Referring to the drawings, the invention will be described with respect to an embodiment thereof. Fig. 1 is an enlarged cross section of a sliding bearing 1 which is formed in semi-cylindrical or cylindrical configuration. The sliding bearing 1 includes a bearing alloy layer 2 which is secured to a backing, not shown, and a circumferentially extending helical annular groove 2a is formed around the inner peripheral surface of the layer 2, thereby defining a circumferentially extending peak 2b between a pair of axially adjacent annular grooves 2a. The surface of the bearing alloy layer 2 is coated by an intermediate layer 3, which conforms to the surface of the alloy layer 2 to present an uneven surface. The surface of the intermediate layer 3 is in turn coated by an overlay layer 4. The purpose of the intermediate layer 3 is to achieve a tight adherence between the alloy layer 2 and the overlay layer 4. With this arrangement, when the overlay layer 4 and the intermediate layer 3 are partly abraded beginning from the surface of the overlay layer 4, the portions of the overlay layer 4 and the intermediate layer 3 which remain within the recess of the annular groove 2a as well as the peak 2b of the alloy layer 2 will be exposed, as indicated by a phantom line L. Referring to Fig. 2, in accordance with the invention, when the height h of the peak 2b and the thickness t of the intermediate layer 3 are taken on the abscissa and the ordinate, respectively, on a graphical representation, the thickness t and the height h are chosen in a range which satisfy the following three inequalities, which range is shown by cross-hatched lines: 1 ≤ h < 5 t ≤ 2h/3 + 1/3 t ≤ 3 where h and t are represented in units of µm. According to another aspect of the invention, the thickness t additionally satisfies the following requirement: t ≤ h/2 It is to be noted that in the illustration of Fig. 1, the scales used in a longitudinal and a transverse direction are greatly different from each other, it being noted that the helical, annular groove 2a desirably has a pitch of 0.2 mm, for example. The range recommended by the Japanese Laid-Open Patent Application cited above is indicated by an area located to the right of a folded line A in Fig. 2. The effect of the invention will be described on the basis of results of tests conducted on the seizure resistance at the beginning of use of the sliding bearing, the seizure resistance and the affinity after the overlay layer 4 is abraded. Referring to the chart shown in Fig. 3, samples 1 to 12 represent products according to the invention in which samples 1 - 9 additionally satisfy the requirement of the inequaliti (4). Samples a to h are located in a range recommended by the Japanese Laid-Open Patent Application cited above, and samples I to V are located outside the both ranges on the graph. Each sample used in the tests includes a backing of SPCC on which a bearing alloy layer 2 comprising 12% by weight of Sn, 1.5% of Pb, 2.8% of Si, 1% of Cu and 0.2% of Cr and the remainder of Aℓ is applied by a pressure welding. An annular groove 2a is formed in the surface of the alloy layer 2 to a required depth with a pitch of 0.2 mm. Subsequently, the surface of the alloy layer 2 is electroplated with Ni to a required thickness to form the intermediate layer 3, on which a 5 µm thick overlay layer 4 comprising 2.5% of Sn and 5% of In and the remainder of Pb is applied by electroplating. The seizure resistance test has been conducted under the following test conditions: Testing machine: Seizure testing machine of journal type Number of revolutions: 1300 rpm Lubricant oil: 10W - 30 Oil temperature: 140°C Mating shaft: S45C hardened, with diameter of 42 mm Bearing clearance: 20 - 50 µm Load pattern: 50 kg/cm 2 for initial 60 minutes, followed by 100 kg/cm 2 during subsequent 45 minutes, and subsequently, the load is increased at a rate of 100 kg/cm 2 evey 45 minutes until the seizure occurs. When testing the seizure resistance after the overlay layer 4 is abraded, the overlay layer 4 is initially formed to a thickness of 2 µm, and assuming heat generated by the bearing during the actual use, a sample which has been overheated at 155°C for 240 hours is employed for determination. During the affinity test, each sample is assembled in a larger end of a connecting rod of seriatum 4-cylinder, 1,600 cc engine, and is subjected to a cycle of an idling phase of one minute and a full load at 6,000 rpm of four minutes, which is repeated over a time interval of five hours. After disassembly, the abutment which each sample is subjected to is determined by a visual inspection into four levels of "excellent", "good", "fair" and "not good". As shown in the chart of Fig. 3, the bearing according to the invention exhibited an excellent result in respect of the seizure resistance at the beginning of the use, the seizure resistance and the affinity after the overlay layer 4 is abraded. By contrast, considering control samples a to h , it is noted that a relatively good result is obtained when the height of the peak is close to 5 µm, namely, from samples a - e having a height in a range of 5 - 7 µm while a poor result is noted when the height of the peak is far greater than 5 µm, namely, for samples f - h having a height in the range of 7 - 9 µm. It will be seen from this that a height of the peak less than 5 µm is required in order to achieve a good performance. On the other hand, from the standpoint of the affinity, it is required that the height of the peak be equal to or greater than 1 µm, and it is noted that the affinity is "not good" for samples I - III having a height less than 1 µm. If the height of the peak is chosen in a range of 1 - 5 µm as according to the invention, if the thickness of the intermediate layer is too thick with respect to the height of the peak, as exemplified by the samples IV and V, the seizure resistance is degraded, in particular, the seizure resistance after the overlay layer 4 is abraded. Accordingly, the requirements as represented by the inequalities (2) and (3) must be satisfied at minimum, and desirably the requirement represented by the inequality (4) should also be satisfied. It is confirmed that the abrasion resistance of the products according to the invention exhibits an abrasion resistance which is on the order of from one and one-half to three times higher than that of the control samples a to h . In addition to those used in the samples, the alloy layer 2 used in the invention may preferably comprise Aℓ-alloy bearing material such as Aℓ - 12% Sn - 1.5% Pb - 2.5% Si - 1% Cu - 0.2% Cr, or Cu-alloy bearing material such as Cu - 23% Pb - 3% Sn or Cu - 15% Pb - 1.5% Sn or Cu - 1% Ag. Preferably, the intermediate layer 3 may comprise Ni, Cu, Cr and Fe which is applied by a wet or dry plating. In addition to those described above, the overlay layer 4 preferably comprises Pb alloy materials such as Pb - 3% Sn - 5% In or Pb - 10% Sn - 2% Cu, or pure Sn or Sn alloy materials. In addition, a synthetic resin material containing polyimide added with MoS 2 or graphite may be used.

Claims: A sliding bearing (1) comprising a bearing alloy layer (2) having a multitude of circumferentially extending and axially spaced annular grooves (2a) formed around the inner peripheral surface thereof to define a circumferentially extending peak (2b) between a pair of axially adjacent annular grooves (2a), an intermediate layer (3) which coats the surface of the bearing alloy layer (2), and an overlay layer (4) which coats the surface of the intermediate layer (3), the arrangement being such that when the overlay layer (4) and the intermediate layer (3) are partly abraded beginning from the surface of the overlay layer (4), the overlay layer (4) and the intermediate layer (3) which remain in the recess of the annular groove (2a) as well as the peak (2b) of the bearing alloy layer (2) are exposed; characterized in that the peak (2b) has a height h, and the intermediate layer (3) has a thickness t, which satisfy the following three requirements: 1 ≤ h < 5 t ≤ 2h/3 + 1/3 t ≤ 3 where h and t are denoted in units of µm. A sliding bearing (1) according to claim 1, additionally satisfying the following requirement: t ≤ h/2 where h and t are denoted in units of µm. A sliding bearing (1) according to Claim 1 or 2 in which the bearing alloy layer (2) comprises a material selected from a group consisting of Aℓ alloy bearing material and Cu alloy bearing material. A sliding bearing (1) according to one of Claims 1 to 3 in which the intermediate layer (3) is formed by a plating of a material selected from a group consisting of Ni, Cu, Cr and Fe. A sliding bearing (1) according to one of Claims 1 to 4 in which the overlay layer (4) comprises a material selected from a group consisting of Pb alloy material, pure Sn, Sn alloy material and synthetic resin material.

Inventors: HASHIZUME KATSUYUKI, KAMIYA SOJI, KUMADA YOSHIO, HASHIZUME, KATSUYUKI, KAMIYA, SOJI, KUMADA, YOSHIO, HASHIZUME, Katsuyuki Taiho Kogyo Co., Ltd., KAMIYA, Soji Taiho Kogyo Co., Ltd., KUMADA, Yoshio Taiho Kogyo Co., Ltd.
Applicants: TAIHO KOGYO CO LTD, TAIHO KOGYO CO., LTD.
Application year: 1995
Main classification: F16C33
IPC codes: F16C33